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Journa l of Consul t ing and C l in ica l Psychology2001, Vol. 69, No. 4, 643-654 In the pub l i c domainDOI : 10.I037//0022-006X.69.4.643

Shaping Cocaine Abstinence by Successive ApproximationKenzie L. Preston, Annie Umbricht , Conrad J. W o n g , and David H. EpsteinNat ional Ins t i tu te on Drug Abuse

Cocaine-us ing methadone-maintenance pa t ients were randomized to s tandard contingency management(abs t inence group, n = 49) or to a contingency des igned to increase contact with re inforcers (shapinggroup, n = 46). For 8 weeks , both groups earned esca la t ing-va lue vouchers based on thrice-weeklyurina lyses : The abs t inence group earned vouchers for coca ine-negative urines only; the shaping groupearned vouchers for each urine specimen with a 25% or more decrease in coca ine metabol i te (first 3weeks) and then fo r negative u rines only ( las t 5 weeks). Cocaine use was lower in the s ha p ing g roup , b u tonly in the last 5 weeks , when the response requirem ent was identica l . Thus , the shaping conting encyappeared to better prepare pa t ients fo r abs t inence. A 2nd phase of the s tudy showed tha t abs t inenceinduced by esca la t ing-va lue vouchers can be ma in ta ined by a nonesca la t ing schedule , sugges t ing tha tc on t ing e nc y managem ent can be pract ica l as a maintenan ce trea tment.

In the subs tant ia l effort expended to find effective therapies fo rcocaine abuse, contingency management has been among the mostsuccessful t reatments to date. Contingency management was de-veloped using operant principles whose effectiveness had beendemonstrated preclinically (Bigelow & Si lve rman, 1999). Cont in-gent re inforcement of target behaviors, such as drug abstinenceand par t ic ipat ion in t reatment activit ies, can be a powerfu l tool inestablishing pos i t ive behavioral changes in drug abusers (Higgins,Sti tzer, Bigelow, & Liebson, 1986; Kidorf & Stitzer, 1996; M c-Ca u l , Stitzer, Bigelow, & Liebson, 1984; Stitzer, Iguchi, & Felch,1992). One of the most effective applications of the procedure hasused a monetary-based escalating-reinforcement schedule in whichthe value of the incentive increases with each consecutive drug-nega t ive urine specimen, whereas lapses (posit ive urine speci-mens) and missed specimen collections result in loss of the incen-tive and a return of the next earned incentive to the original value(Higgins e t al., 1991, 1993, 1994). This procedu re has been usedsuccessfully in a number of c l in ics , inc lud ing our own (Kirby,Marlowe, Festinger, Lamb, & Plat t , 1998; Silverman et al., 1996,1998).Most studies using contingency management have made thede l ive ry of incent ives cont ingent on d rug-negat ive ur ine speci-mens (i.e., reinforcement of abstinence). Although this technique

Kenzie L. Pres ton, Ann ie Umb richt , Conrad J . Wong, an d David H.Eps te in, Intramura l Research Program, Nationa l Ins t i tu te on Drug Abuse,Bal t imore , Maryland.Conrad J . Wong is now a t the Department of Psych ia try and Behaviora lBiology, Johns Hopkins Univers i ty School of Medicine.This s tudy was supported by the Intram ura l Research Program of theNational Ins t i tute on Drug Abuse. We are grateful to the Archway trea t-m e nt staff and technicians ; to Kenneth Silverman an d Charles R. Schus terwho helped des ign the cl inica l t ria l ; to Robert Broo ner who monitored themethadone-maintenance trea tment; and to A nna DeJe s us w ho assisted inth e c o n d u c t of this s tudy.Correspondence concerning this a r t ic le should be addressed to KenzieL. Preston, In t ramura l Research Program, Nationa l Ins t i tute on DrugAbuse, 5500 Nath an Shock Drive, Bal t imore , Maryland 21224. Electronicmail may be sent to kpr e s t o n @ i n t r a .n i d a .n i h .go v .

has been effective for many patients, experience in our clinic hasshown that some part icipan ts who reduce their cocaine use will notimmediately produce negative urine specimens. Cocaine ur i nescreens are typically considered posit ive above a cutoff of 300ng /ml in benzoylecgonine equivalents (BZE); benzoylecgonine,the major metaboli te of cocaine, has a urinary excretion half-lifeof 6 to 8 hr (Ambre, 1985) and can usual ly be detected for 48 hr(Saxon, Calsyn , Haver, & Delaney, 1988). In some cases, patientsmay cease or reduce their cocaine use, yet go unreinforce d becausenot enough t ime ha s elapsed before sample collection, esp ecially ifinitial BZE levels were high. For example, in patients who hadappeared unrespons ive to a voucher cont ingency in one of ourearlier studies (Silverman et al., 1996), quanti tat ive urinalysesshowed significant decreases in BZE levels (from a mean ofapproximate ly 60,000 ng/ml during baseline to approxi-mately 30,000 ng /ml d u r i ng th e voucher cont ingency) . Thesepat ients had presumably reduced their cocaine use, yet they re-ceived few or no vouchers because their BZE concentrationsremained above the standard cutoff . Upon not receiving a voucher,such patients may have become discouraged and relapsed to druguse before achieving abstinence of adequate duration to have anegative urine screen.

In th i s s tudy we tested a var ia t ion of cont ingency managementin which incentives were ini t ially given fo r decreases in BZEconcentrations and subsequently were given only for samplestest ing negative for BZE at the standard cutoff . Reinforcement ofsuccessive approximations of a desired behavior ( in this case,cocaine abstinence) is known in the operant condit ioning li teratureas shaping (Catania, 1973). Shaping has an extensive history fo rt raining desirable behaviors in nonhumans and has been usedsuccessful ly to modify behavior in c l inical popula t ions as well(e.g., se e Catania, 1973; Meyer & Chesser, 1970). W e hypothe-sized that patients would be more likely to reach th e ul t imate goalof cocaine abs t inence if incremental decreases in BZE concent ra-t ions were reinforced early in t reatment. This shaping of absti-nence was compared with a more typical contingency procedure inwh i ch incentives were given only fo r samples test ing negative fo rBZE at the s tandard cutoff .

643


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644 PRESTON, U M B R I C H T , W ON G , A N D EPSTEI NA secondary goal of the study was to evaluate the use of amaintenance cont ingency as a fol low-up to the escala t ing-re inforcement procedure. Patients who completed the main inter-

vent ion phase of the present study were switched to a nonescalat-ing reinforcement schedule (with fixed-amount vouchers an d take-home doses given as incent ives fo r negative urine specimens). Thisw as tested against a control procedure in w hi c h th e samef ixed-amoun t vouchers an d take-home doses were givennoncon t ingen t ly .

MethodParticipants

Par t ic ipan ts were selected from 28 5 patients consecutively admitted fo rm e th adone maintenance a t Arch way Cl inic , the trea tment research programof th e Nat ional Ins t i tu te on Drug Abuse Intramura l Research Program inBalt imore, M D . Appl icants were first screened by te lephone and then intw o on-s i te visits tha t included medica l , psychia tr ic , and drug-use his tor ies ,a phys i ca l exa mina t ion , u r ine and blood screens, and a battery of assess-m e nt ins t ruments : Addict ion Severi ty Index (McLel lan e t a l . , 1985); Na -t iona l I ns t i tu te on Menta l Heal th D iagnos t ic In terview Schedule (Helzer,C roug h an , R obins , & Ratcliff, 1981); Beck Depress ion Inventory (B DI ;Beck & Steer , 1987); Symptom Check Lis t90Revised (SCL-90-R;Derogat is , 1977); and the Shipley Ins t i tute of Living Scale (Zachary,1986). Persons were eligible for the s tud y if they were between 18 and 65years of age, if they qual i f ied fo r methadone maintenance accord ing toFood an d Drug A d mini s t r a t ion gu id e line s , and if they reported histories ofintravenous opiate use. Two studies were conducted concurrently, thiss tudy focusing on coca ine use and the other focus ing on opiate us e(Preston, Umbricht , & Epste in, 2000). Patients were eligible for the opiateor coca ine s tudy if at least 3 of 15 ur ine specimens col lected during a5-week basel ine trea tment phase tes ted pos i t ive fo r morphine (heroinmetaboli te ) or BZE, respectively. Patients who met the criteria for cocainebu t not for opiates were assigned to the present cocaine st udy . Patients w homet the cri ter ia fo r both drugs were randomly ass igned to one of thestudies. Persons with current major psychiatric il lness or uns table ser iousmedical i l lness were excluded. The local ins t i tu t ional review board fo rh u m a n research approved this s tudy, and al l part ic ipants gave informedwri t ten cons en t p r io r to part ic ipa t ion.Standard Treatment

Al l part ic ipants received, without charge, s tandard methadone mainte-nanc e tha t consisted of da ily methadone an d weekly individual counselingt h r o u gho u t the 25-week s tudy. Methadone HO (Mall inckrodt , St. Louis,MO ) w as adminis tered ora l ly in a cons ta n t vo l ume (35 ml) of a cherry-f lavored so lu t ion . Metha d one dose w as stabil ized at 50 mg within th e f irstweek of t r e a tment an d held cons tant through th e 25-week s tudy. Counsel -in g sess ions were problem focused and included both support ive andmotiva t ional techniq ues . Counselors completed a semis tructured psycho-socia l assessment and master t rea tment plan fo r each participant thatguided the focus of a l l counsel ing sess ions . Reduc tion of subs tance use wasth e pr imary goal. Counselors helped participants develop a funct ionalanalys is of their subs tance use , identify an d avoid high-r isk subs tance us es i tua t ions , a void f r iends an d acquaintances w ho used drugs, cope withurges to use drugs , an d examine acute an d long-term consequences of druguse .Urine and Breath Toxicology

Each Monday, Wednesday, and Friday urine specimens were collectedunde r th e observa tion of trained laboratory technicians. W e conductedqua l i t a t ive testing with a n enzyme mult ipl ied im m unoassay technique

(Syva, Palo Alto, CA) system that gave qualitative results for cocaine(BZE), opia tes (morphine) , benzodiazepines (oxazepam), phencycl id ine ,barb i turates, and marijuana . Cutoff concentrations fo r pos i t ive specimenswere 300 ng /m l for cocaine, opiates, and benzodiazepines; 25 ng /m l fo rPCP; and 50 ng/ml for marijuana . BZE concentra t ions were measured byfluorescence polar iza t ion immunoassay (FPIA) us ing TD x Cocaine M e-tabolite Assay reagents (TDx; Abbott Laboratories, Abbott Park, IL) on aTD x instrument. Cross-reactivity wa s 100% for BZE and less than 1% fo rcocaine, ecgonine methyl ester, an d ecgonine. Th e assay provides accuratequant i ta t ion for concentra t ions between 30 and 5,000 ng/ml ; specimenswith concentra t ions higher than 5,000 ng/ml were diluted to concentra t ionswithin the 30 to 5,000 ng/ml range an d reanalyzed. Breath alcohol levelswere determined with an Alco-Sensor III (Intoximeters, St. Louis, MO).

Self-Report QuestionnairesWe collected participants ' self-reports of drug use immediately after

each urine collection. Participants were asked whether they had used, theam oun t and nu mb er of times used, and the dollars spent on alcohol, opiates,coca ine , benzodiazepines , phencycl id ine , or marijuana on each day s incetheir last cl inic visit. On Wednesdays, participants completed a cravin gques t ionnaire and the Lifes tyle Changes Ques t ionnaire (Silverman et al.,1998). On the craving qu es t ionnaire , part ic ipants ra ted how m uch they hadwanted coca ine an d heroin during th e past week on a scale from 0 (not atall) to 4 (extremely). On the Lifestyle Changes Questionn aire, p articipantsindica ted whether they ha d engaged in any of nine act ivi t ies to stop,reduce, or avoid coca ine/heroin use during th e past week (analyzed as totalnum b e r o f items endorsed) an d whether they ha d engaged in any c r imina lactivity.

Study Timeline and GroupsThe s tudy was conducted in three con secutive phases : a 5-week basel ine

trea tment phase, an 8-week intervention, and a 12-week maintenancephase. Baseline began on s tudy enrol lment and continued unt i l th e partic-ipant had provided 15 urine specimens, typically at the end of 5 weeks. Atthe end of baseline, participants were randomized to one of two interven-tion groups , an experimenta l group re inforced fo r decreases in drug use anda control group re inforced for coca ine-negative urine specimens only. Atthe end of the intervention, part ic ipants remaining in trea tment wereoffered 12 weeks of addit iona l methadone main tenance; ha l f of the part ic-ipants in each group were random ly ass igned to con t inue on a ma in tena ncecontingency or to switch to a noncontingent condit ion. (This "rerandom-iza t ion" aspect of the study design is similar to that used in the Pittsburghstudy of maintenance trea tments fo r depression; Kupfer e t al., 1992.)Trea tment an d data collection otherwise remained th e same throughout th es tudy.

Intervention

During the intervention, all participants could earn vouchers on the basisof urine specimens collected every Monday, Wednesday, and Friday. Theabs t inence group (n = 49) earned vouchers for each urine specimen thattested cocaine negative on the qualitative urine screen at the 300 ng/mlBZE cutoff. This criterion for earning vouchers was in place throughoutthe 8 weeks of intervention. Patients in this group received th e fol lowinginstruction at the beginning of the intervention: "For the next 8 weeks, youca n earn vouchers fo r provid ing urine samples which indica te tha t yo u haveno t used cocaine." The shaping group (n = 46 ) earned vouchers for eachurine specimen whose BZE concentration was 25% or less than that of thespecimen collected 48 hr to 72 hr earl ier during the previous clinic visit orless than 300 ng/ml . This shaping contingency was in effect for 3 weeks ,fol lowed by 5 weeks of an abs t inence contingency ( identica l to the one


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SH A PI N G COCA I N E A B STI N EN CE 645used for the abs t inence group). Pa t ients in this group received the fol lowingins truct ions :

For the next 8 weeks , you can earn vouchers for provid ing urinesamples which indica te tha t you have decreased your use or not usedcocaine. During the f irs t 3 weeks we wil l measure the amo unt ofcoca ine in your u r ine . If the a m o u n t of coca ine in your u r ine isdecreased by at least one quarter (25%) compared to your previousurine sample , you wil l earn a vouc her. You wil l also receive a voucherif your urine sample is coca ine-free during Weeks 1 to 3. DuringWeeks 5 to 8, you wil l earn vouchers only if your ur ine sample iscocaine- free .

The 25% cri ter ion was chosen to reflect what we thought would bec l in ical ly s ignif icant decreases in use and was based on earl ier work in ourc l in ic showin g tha t a 50% decrease in BZE conc entra t ion genera l ly ind i-ca tes abs t inenc e (Preston, Silverma n, Schus ter , & Cone, 1997).

The voucher in centive program was based on tha t developed by Higginsan d colleagues (Higgins et al . , 1991, 1993, 1994). The values of thevouchers were the same for both groups . Values began a t $2.50 an dincreased in value by $1.50 fo r each consecutive voucher earned. Inaddition, for every three consecutive vouchers earned, participants receivedan addit iona l voucher worth $10. A part ic ipant who met the cr i ter ia forearning a voucher for 8 consecutive weeks could earn a tota l of $554(average $9.89 per day). If the participant did not meet the criteria forearning a v oucher, the part ic ipant d id not receive a voucher, and the va lueof the next earned vo ucher w as reset to $2.50. Earned vouchers were givento part ic ipants the day after ur ine col lect ions (Tuesday, Thursday, andSaturday). The vouchers were exchangeable for goods and services (e .g . ,passes to the movies , exercise equipment, dr iver ' s l icense , or gift cert if i-ca te) tha t would support a drug-free l i fes tyle . When th e part ic ipant accu-mula ted enough vouchers to purchase a desired item, a staff memberreviewed the reques t to determine w hether the des ired i tem was cons is tentwith tha t part ic ipant ' s t rea tment goa ls . I tems were purchased by staffmemb ers and given to part ic ipants in the cl inic; no m oney was givendirec t ly to part ic ipants .

Maintenance ContingencyA t the end of the intervention phase , part ic ipants were rerandomized to

one of two ma in tena nce cond i t ions : con t ingen t or noncontingent. Part ic i-pants in the contingent group received a $10 voucher for each coca ine-negative specimen submitted for the thr ice-weekly u rine tests . In addit ion,if part ic ipants had two out of three coca ine-negative u rine specimensdur ing the week, they received a dose of methadone on Sa turday to take a th om e on Sunday. Part ic ipants ass igned to the noncont ingen t g roup re -ceived vouchers and take-home doses indepen dent of their ur ine resul ts .Each non contin gent group part ic ip ant was rand om ly yoked to a part ic ipan tin th e contingent group, independent of in te rven tion g roup a s s ignment . Fo reach cl inic visit numbered from 1 to 36 (3 per week fo r 12 weeks) tha t th ec on t ing e n t part ic ipan t earned a vo ucher or take-home dose for tes t ingcoca ine-negative , th e non con tinge nt part ic ipant received an identica lvoucher or take home dose fo r provid ing urine . If the n o n c o n t i n g e n tpart ic ipant d id not provide a ur ine specimen or d id not a t tend cl inic , theincent ive was forfe i ted; part ic ipants were not told when this occurred .Rules fo r us ing vo uche r s r ema ined as in the intervention phase; unusedvouche r money a ccum ul a ted across the entire s tudy and could be used forup to 1 year after study part ic ipa t ion ended.Data Analysis

Because part ic ipants were rerandomized into new groups between theintervention and main tenanc e phases , da ta from the two phases wereanalyzed separately (b ut similar ly). The analyses described here apply toboth phases , with exceptions as noted .

To ensure comparabil i ty between groups , w e analyzed intake measuresby analys is of variance (ANOVA; for continuous variables) , Pearson ch isquare (for categorical variables), or Fisher's exact test (for categoricalvariables with expected cell sizes less than 5) . Retention rates werecompared between groups with surviva l ana lys is , by us ing a log-rank tes tof time until the provision of the final urine sample; participants who leftbefore the final week of the experimental phase ( intervention or mainte-nance) were coded as dropouts . Part ic ipants with three or more sporadi-ca l ly miss ing u rine tes ts (i.e., not because of dropout) du ring the experi-mental phase were coded as poor a t tenders ; this was compared betweengroups with Fisher's exact tes t . Voucher earnings were compared byA N O V A ; percentages of part ic ipants never earning a voucher were com-pared by Pearson chi-square tes t .The t ime course of coca ine u se during interv entio n was ana lyzed withgeneralized l inear mixed models fi t with the SAS macro GLIM MIX (Lit te l ,Mill iken, Stroup, & Wolfinger , 1996). GLIMMIX analyzes d ichotomousrepeated m easures with miss ing da tapoints by invoking the SAS procedu reMI XED w i th a logit l ink (SAS, 1997) and gives adjusted proportions. Afirs t-order autoregress ive error s tructure was used. Continuous measurestaken a t repea ted t imepoints during intervention (such as BZE levels ,craving, se l f- reported u se , and l i fes tyle changes) were ana lyzed with mixedregressions (SAS MIXED procedure) . Each model con ta ined one within-subjec t factor (Time) an d four between-subjects factors : contingency,basel ine percentage nega tive (or mean), poor a t tendance, and dropout(Hedeker & Gibbons , 1997). Analyses of maintenance-phase da ta con-trolled for pr ior contingenc y as an addit iona l be tween-subjects factor; somemaintenance-phase analyses a l so control led fo r intervention percentagenegative .

In the interventio n phase , e ight intake measures d iffered between groupsat p s.10; in the maintenance phase , five intake measures d ifferedbetween groups a t p & .10. To control for po tentia l con foun ding , wecons idered each intake measure fo r inclus ion in the G L I MMI X and mixed-regression models if it had a ma in effect on the outcome mea s ure at ps.05 and if tha t effect remain ed s ign i f ican t w hen it was entered into a modelwith th e factors l isted in the previous paragraph. In no case di d tha t occur.

Because the BZE da ta were heav ily r ight-skewed, a l l nonzero va lueswere log- transformed (D elucchi, Jones , & Batki , 1997) to reduce thein f luence of extremely high values before th e data were entered into amixed-regress ion model .

Longes t du ra t ion of coca ine abs t inenc e was ca lcula ted for each p art ic-ipant as the longes t run of consecutive coca ine-negative urine specimensduring intervention and main tenanc e phases ; groups were compared by anA N O V A .

Al l analyses were two-ta i led; a was set at .05, with trends noted at .10.

Resul tsParticipant Characteristics

Of the 285 part icipants who enrolled in the study, 253 com-pleted th e 5-week baseline. O f these 253, 22 participants met thecriteria for cocaine use o nly, 29 met the criteria for opiate use only,an d 190 participants met the cri teria for both opiate and cocaineuse. Twelve patients did not meet cri teria for e i ther drug; theyreceived standard treatment for the durat ion of the s tudy. A tota lof 95 participants were randomized to one of two groups in thepresent s tudy; the two groups did not differ in terms of drugcri teria met, x*(l, N = 95) = 0.38, p = .54. Their demographicinformation is shown in Table 1. A mong the 43 demographicvariables compared, e ight differed across in te rvent ion groups a tp < .10: The shaping group ha d more i l legal income, more yearsof sedative use, more recent days of cocaine use, more recent daysof heroin use, higher BD I scores, and more psychia t r ic symptom-


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646 PRESTON, UMBRICHT, WONG, AN D EPSTEINTable 1Demographic Characteristics of Patients

Intervention phase

VariableAge (in years; M SD )Male (% )African American (% )Marital status (%)MarriedDivorced/widowedNever marriedSeparatedEmployment (%)

F u l l t imePart timeUnemployedIncome past 30 days(U.S. $; M SD)LegalIl legalEducation (in years;M SD)Self-reported l i f e years ofdrug us e (M SD)HeroinCocaineAlcoholSedatives/tranquilizersMarijuanaDrug use in past 30 days

(M SD)HeroinCocaineAlcoholSedatives/tranquilizersMarijuanaCurrent DSM-III-Rdiagnosis(% of Ss; from DIS)PhobiaPTSDAntisocial personalityNicot ine dependenceHeroin dependenceCocaine dependenceAlcohol dependenceSedative dependenceBD I (M SD)SCL-90-R GlobalSeverity Index(M SD fShipley Ins t i tute of LivingScale (M SD)

VocabularyAbstract thinkingPrior cont ingenc yAbst inence (% )Shaping (% )

Abstinence( = 49)38.2 6.15152

14184127271657

642 47870 7611.5 1.8

15.2 7.66.0 7.53.6 6.20.02 0.13.6 6.222.3 1 1 . 49.9 10.04.1 7.30.2 0.60.8 1.9

621853965310417.5 10.560.4 8.8

39.7 9.947.9 9.0

Shaping(n = 46)

37.9 5.3595922204613281557

71 5 526868 1,91911.6 1.9

12.3 8.36.6 6.04.4 8.00 .7 2 . 14.0 6.7

25.9 8.315.8 10.53.7 7.00.9 3.01.0 2.8

13275298597421.6 10.367.7 10.4

39.9 10.848.4 9.7

Analysis"F ( l , 9 3 ) = 0.06^(1) = 0.56^(D = 0.47^(3) = 3.04

X*(2) = 0.05

F(l, 93) = 0.52F(l, 93) = 8.39F ( l , 93 ) = 0.18F ( l , 9 3 ) = 3.18F(l, 93) = 0.18F ( l , 93 ) = 0.28F(l , 93) = 4.43F ( l , 9 3 ) = 0.11F(l, 93 ) = 3.13F(l, 93) = 7.84F(l, 93) = 0.11F(l, 93) = 2.46F(l, 93) = 0.22

^(1) = 3.02^(1) = 0.01^(1) = 0.31

F(l, 93) = 3.62F ( l , 9 2 ) = 13.53

F(l, 93) = 0.01F(l, 93) = 0.06

P.81.45.49.39

.98

.47


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SHAPING COCAINE ABSTINENCE 647atology on the SCL-90-R but had fewer years of heroin use and alower prevalence of Antisocial Personality Disorder.

After completing the intervention, 80 participants were reran-domized to one of the maintenance groups. The demographiccharacteristics of the rerandomized maintenance groups are alsoshown in Table 1. The groups did not differ in terms of prior groupduring intervention. Five demographic variables differed acrossgroups at p < .10: The contingent group had less legal income,more years of alcohol and marijuana use, more recent days ofcocaine use, more recent days of marijuana use, and lower prev-alence of nicotine dependence.Intervention Phase (Shaping vs . AbstinenceContingencies)

Retention, missing urine specimens, and voucher earnings.Overall, 80 (84%) of 95 participants completed all 8 weeks ofintervention. Survival analysis showed no significant between-groups difference in retention rates. Groups also did not differ inn u m b e r s of missed urine specimens (Table 2).

Total voucher earnings did not differ between groups, but then u m b e r of vouchers earned in the first 3 weeks was significantlyhigher in the shaping group (Table 2). Participants in the absti-nence group were significantly more likely to fail to contact thereinforcer (i.e., to earn at least one voucher), even during the

final 5 weeks of intervention, when the response requirement forthe two groups was identical (Table 2).

Cocaine useurine screens. Overall, approximately 15% ofa ll urine specimens were cocaine negative during the 5-weekbaseline, with participants in the shaping group having aslightly, though not significantly, higher proportion of negativeurines (Table 3; Figure 1). The trend during baseline was for therate of negative urine specimens to decreasethat is, for use toincrease. This trend was reversed in both groups with the onsetof th e contingent-voucher invention, resulting in a significanteffect of phase (baseline vs. intervention, see Table 3). Duringthe first 3 weeks of intervention, the percentage of cocaine-negative urine specimens increased similarly in both groups(Figure 1). At the end of the third intervention week, when thes h a p i n g group was switched to the more stringent requirementof earning vouchers for cocaine-negative urine specimens, thepercentage of cocaine-negative urine specimens in that groupincreased fu r the r . No corresponding increase occurred in theabstinence group. Data from the intervention phase were en-tered into a generalized linear mixed model, controlling fordropout, poor attendance, and each participant's percentage ofcocaine-negative urine specimens during baseline. There wasno main effect of group, b u t there was a s i g n i f i c a n t Group XD ay interaction, F(23, 1842) = 2.13, p < .002), reflecting the

Table 2Retention, Missing Urine Specimens, and Voucher Earnings During Intervention and Maintenance

Variable Abstinence Shaping Analysis

Reached Week 8 of intervention, nCompleted Week 8 of intervention, nTotal weeks in treatment, including baseline

(M SD )Sporadically missing urines d uring interventionM SD% poor attendersaVoucher earnings (U.S. $; M SD)Number of vouchers earned in first 3 weeks(M SD)Number of vouchers earned in final 5 weeks(M SD)Participants earning no vouchersFirst 3 weeks, nFinal 5 weeks, nThroughout intervention phase, n

Number enrolledReached Week 12 of maintenance, nCompleted Week 12 of maintena nce, nTotal weeks in treatment, including b aseline(M SD )Sporadically missing urines during maintenanceM SD% Poor attenders"Voucher earnings (U.S.$; M SD)Number of take-home doses of methadone(M SD)

Intervention43 (88%)43 (88%)

12.34 1.931.12 1.9416$101 1852.69 3.313.71 5.76

23 (47%)27 (55%)19 (39%)Maintenance

4136 (88%)34 (83%)24.5 1.71.2 1.59.8$135 1324.4 7.7

phase40 (87%)37 (80%)

12.23 2.040.87 1.059$115 1705.09 2.525.17 5.51

2(4%)14 (30%)2 (4%)phase

3935 (90%)34 (87%)24.7 1.11.6 1.728.2$119 1263.7 4.6

Log-rank /(I) = 0.83F(l, 93) = 0.06F(\, 93) = 0.61^(1) = 1.25F ( l , 9 3 ) = 0.15F(l , 93) = 15.60F(l , 93) = 1.60^(1) = 22.20^(D = 5.88/(I) = 16.33

Log-rank ^(1) = 0.25F(l, 78) = 0.23F ( l , 78) = 1.91/(I) = 4.47F ( l , 78) = 0.30F(l, 78) = 0.46

.36

.80

.44.26.70


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648 PR ESTON , UMB R I CH T, W O N G , A N D EPSTEINTable 3Urine Test Results During Intervention: Mean Percentage of Drug-NegativeSpecimens an d Standard Deviation

G rou p A N O VAAbstinence

VariableCoca ine -nega t ivebBase l ineInte rvent ionOpia te negative15Basel ineIn terven t ionBenzodiazepine negative15Basel ineIn te rvent ionC annab i s negat ive6Base l ineInte rvent ionAlcohol -nega tive0Base l ine

Inte rvent ion

M

12275858938984869894

SD

1837293816242927

521

Shaping Phase Phase X GroupM

17336157959290879899

SD F "131.432034 0.1223

30 5.481417 0.612427 1.6154

P F- p< .001 2.01 .16

.73 0.39 .54

< .02 0.05 .82

.44 0.73 .40

.21 3.80 < .06

Note. A N O V A = analysis o f var iance.8 d fs = 1 , 9 3 . b Urine spec imens. c Breath specimens.

s up e r i o r pe r f o r m a n ce of the sh a p in g g r o u p du r in g th e la t te r pa r tof the i n t e r v e n t i o n .Other measures of coca ine use also appeared to favor th e shap-in g in tervent ion , t h o u gh not to a statistically signif icant degree.Mean BZE levels were 48,389 (SEM = 8,644) ng/ml in theshap ing gr o u p and 56,340 (SEM = 8,626) in the abst inence group,mixed regression, F(l, 90) = 1.70, p = .20. The longest dura t ionof abst inence , in fer red from consecut ive nega t ive specimens, av-eraged 5.5 (SEM = 1.1) in the shaping group and 5.1 (SEM = 1.2)in the a bs t in e n ce g r o u p , A N O V A , F(l, 93) = 0.04, p = .83; thedifference remained nons ign i f i can t in an ana lysis of covariancecont ro l l ing fo r each p ar t ic ipant ' s base l ine percentage nega t ive .

Use of other drugs. There were only minor changes in otherdrug use f rom baseline to intervention, with rates of use similaracross the two in te rvent ion groups (Table 3) . There was a signif-i can t effect of phase (baseline vs . in te rvent ion) on percentage ofbenzodiazepine-negat ive urine specimens, with both groups hav-in g sl ight ly fewer nega t ive specimens dur ing th e in te rvent ion . Th enear-s ignificant (p = .054) Phase X Group in terac t ion fo r alcoholreflects th e s l igh t ly greater tenden cy for the abst inence group totest posi t ive fo r a lcohol dur ing th e in te rvent ion . In both cases,however , the rates of positives fo r benzodiazepines an d alcoholwere relatively low and of doubt fu l cl in ica l s ign if icance .

Self-reported cocaine use, heroin use, cocaine craving, positivelifestyle changes, an d criminal activity. Self-reported frequencyof coca ine use tended to be higher dur ing baseline in the shapinggroup than in the abst inence group; thus , when in tervent ion da tawere ana lyzed in a mixed regression controlling fo r baseline, therewas a trend toward a m a in effect of group, favoring th e shapingintervent ion (Table 4) . There were no signif icant group differencesin other self-reported indices of coca ine or heroin use, drug crav-ing, lifestyle changes, or criminal activities (Table 4) . However ,s ignificant improvem ents occur red from base l ine to intervention

(in both groups) in f requency, amount , and cost of heroin use, incraving for cocaine and heroin, and in c r iminal activities (repeated-measures ANOVAs on whole-phase means; data not shown).Maintenance Phase (Abstinence Contingency vs .Noncontingent Vouchers)

Retention, missing urine specimens, an d voucher earnings.Eighty participants com pleted the intervention and were rerandom-ized, with approximately half of each intervention group assignedto each of the contingent and noncontingent maintenance groups.Sixty-eight (85%) of the 80 participants com pleted all 12 weeks ofmaintenance. Survival analysis showed no signif icant between-groups difference in retention rates during either phase. Groupsalso did not differ in n u m be r s of missed urine specimens, in totalvoucher earnings, or in number of take-home doses of methadone(Table 2) . However, there were signif icantly more poor attenders(participants missing three or more ur ine specimens) in the non-cont ingent group; this w as controlled for in mixed models.

Cocaine use urine screens. For the contingent group, thepercentage of cocaine-negative ur ine specimens f luctuated around40%; for the noncontingent group, i t f luctuated around 20% (Fig-ure 2). There was substantial day-to-day variabili ty in each group,bu t no clear upward or downward trend in either . Before testingbetween-groups differences, we noted that the contingent groupoverrepresented participants who had already achieved high de-grees of abstinence during intervention. Therefore, each partici-pant 's percentage of cocaine-negative ur ine specimens during in-tervention was included as a covariate in a generalized linearmixed model; th e other covariates were dropout, poor attendance,pr ior contingency, and maintenance group (contingent vs. noncon-t ingent). The main effect of maintenance group w as signif icant,F(l, 73) = 6.58, p < .02. Adjusted percentages of cocaine-


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SHAPING COCAINE ABSTINENCE 649601

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75Baseline Intervention MaintenanceNumber of consecutive urine specimens

Figure 1 . Percen tage of par t ic ipan ts cocaine a bs t i n en t on 75 success ive u r ine tes t days in the basel ine phase(1 5 specimens), in terven t ion phase (2 4 specimens), an d m a i n t en a n ce pha s e (3 6 specimens) in the two t r e a t m en tgroups: abs t inenc e group (vouchers fo r coca ine-negat ive u r ine specimens on ly ), shaping group (vouchers fo rdecreased cocaine metabolite concen t ra t ion for 3 weeks fo l lowed vouchers for coca ine-negat ive u r ine specimenson ly). Data shown here are raw percen tage va lues ; miss ing specimens ( including those due to dropout) aret r ea ted as posi t ive . For the abs t inence group, n = 49 in the basel ine and in terven t ion phases and 43 in them a i n t en a n ce phase; for the s ha p i n g g r o u p , n = 45 in the basel ine an d in terven t ion phase and 37 in them a i n t en a n ce phase. Note tha t the shaded area represen ts the on ly por t ion o f the s tudy dur ing which the twogroups were t rea ted d i f feren t ly (see in terpre ta t ion in Discuss ion). Dur ing the main tenance phase, par t ic ipan tswithin each grou p were rerand omized to new c on t ingencies (see Figu re 2); da ta in this figure a re co l lapsed acrossthose con t ingencies .

negat ive ur ine spec imens were 7% in the nonc ont ingen t group and22% in the cont ingent group. (These pe rcentages appear lo wbecause they ar e adjusted for all effects in the model , inc lud ingeach pa r t ic ipant ' s ear l ie r pe rcentage of negat ive ur ine spec imens .We present them here for in te rgroup compar i sons ra the r than asabsolute indicators of pe rformance . ) Th e effect of pr ior cont in-gency is discussed below.The longest duration of abstinence, inferred from consecut ivenegat ive spec imens , showed a t rend toward be ing s igni f icant lygreater in the co nt ingent group (M = 8.2, SEM = 1.7) than in then o n co n t i n g e n t g roup (M = 4.3, SEM =1.0), F(l, 78) = 3.92, p =.051.

Use of other drugs. There were no signif icant be tween-groupdifferences in use of o t he r d rug s d u r i ng m a i n t e nanc e as determinedin ur i ne or breath screens (Table 5) .Self-reported cocaine use, heroin use, cocaine craving, positive

lifestyle changes, an d criminal activity. There were fe w differ-ences be tween the maintenan ce groups on se l f- repor ted measures(Table 6). Trends (p < . 10) toward s igni f icant Group X W eekinteractions occurred only in mean dollars spent on cocaine perday and m e a n a m o u n t o f heroin used per day.

E f f e c t of prior contingency. One of the mixed models (de-scribed above in the section Cocaine use urine screens) enabledus to evaluate th e effect of pr ior cont ingency (shaping vs. absti-nence) whi le cont rol l ing for current cont ingency and othe r var i -ables. The effect of pr ior cont ingency was not s igni f icant , F(l,73) = 1.21,/ j = .27, but par t ic ipants formerly in the shaping groupdi d tend to maintain higher rates of cocaine-negative urine than didparticipants formerly in the abstinence group, regardless of reran-domiza tion (Figure 1). Adjusted percentages of cocaine-nega tiveurine specimens were 26% (former shaping) versus 19% (formerabstinence) in the abs t inence groups and 10% (former shaping)versus 4% (former abs t inence) in the noncont ingent groups . Asbefore, we present these adjusted percentages for intergroup com-par i sons rather than as absolute ind icators of pe rformance .

DiscussionT he r e s u l t s s how t ha t c on t i ng e nc y manag e me n t fo r c oc a i neab us e c an b e more e f fe c t i ve w he n i n t rod uc e d i n a s t e p w i s efash ion . R e i n fo rc e me n t o f decreases in ur ine BZE concent ra-t i ons p r i o r t o i n i t i a t i on o f ab s t i ne nc e r e i n fo r c e me n t ( s hap i ng


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650 PRESTON, UMBRIC HT, WONG , AND EPSTEINTable 4Self-Reported Cocaine an d Heroin Use, Craving, Lifestyle Changes,an d Criminal Activity Intervention

Grou p Mixed regressionAbst inence Shaping Group Week

VariableSelf-reported cocaine use 8Mean frequency per dayBaselineInterventionIntervention (adj)bMean amoun t per day (mg)Basel ineInterventionIntervention (adj)bMean dollars spent per dayBasel ineInterventionIntervention (adj)bSelf-reported heroin usea

Mean f requency per dayBasel ineIn te rvent ionIntervention (adj)bMean amount per day (mg)Basel ineInterventionIntervention (adj)bMean dol lars sp ent per dayBasel ineInterventionIntervention (adj)bWeekly self-report questionnaireC oc a i ne cravingcBasel ineInterventionIntervention (adj)bHeroin craving 0Basel ineInterventionIntervention (adj)bLifestyle changes '1BaselineIn te rvent ionIntervention (adj)bCriminal activities'1Basel ineInterventionIntervention (adj)b

M

0.320.310.5430.429.881.6

2.181.943.53

0.150.110.150.190.120.251.210.781.16

1.561.511.571.431.160.973.744.023.880.070.020.001

SD M SD F p F p

0.26 0.46 0.410.35 0.30 0.320.49 0.47 0.47 2.98 < .09 1.20 .2330.3 44.2 49.740.7 55.4 206.1186.2 84.4 181.8 0.09 .77 0.90 .60

3.05 2.69 3.033.15 2.02 3.104.83 3.08 4.75 0.49 .49 1.04 .41

0.15 0.18 0.160.18 0.11 0.120.21 0.13 0.20 0.55 .46 1.23 .210.18 0.29 0.590.19 0.22 0.730.49 0.23 0.47 0.12 .73 1.00 .471.48 1.39 1.831.41 0.64 1.031.89 0.90 1.83 1.23 .27 0.96 .52

0.77 .52 0.840.94 .27 0.961.12 .35 1.09 2.52 .12 1.73 .101.03 .39 1.061.21 .20 1.081.47 1.03 1.36 0.13 .72 1.13 .342.21 4.22 1.732.64 4.05 2.132.87 3.53 2.78 0.90 .35 1.21 .290.19 0.17 0.530.14 0.05 0.160.03 0.04 0.03 1.76 .19 1.07 .38

Group X WeekF P

0.76 .79

0.75 .80

0.85 .67

0.45 .99

1.01 .44

0.98 .50

0.58 .77

0.38 .91

0.88 .53

1.35 .22Note. Adj = adjusted.a Data w ere available for 95 participants. Degrees of freedom are (1, 90) for grou p and (23, 1927) for t ime andGroup X Time. b Adjusted means control for baseline, dropout, and poor attendance; they are presented hereas in tergroup compar isons ra ther than as absolute indicators of performance. c Data were available for 93participants. Degrees of freedom are (1, 88) for group and (7, 534) fo r time an d Group X Time. Craving wa srated on a scale of 0-4. d Data were available for 93 par t ic ipants . Degrees of freedom are (1, 88) for gr oup and(7, 534) for t ime and Group X Time. Lifestyle changes are reported as the mean sum of the i tems reported perweek. Criminal activit ies are the mean of the total reported per week.

group) resu l ted in lower coca ine use (as indica ted by morecoca ine-nega t ive ur ine specimens) than did a co n t in ge n cy th a tre inforced o nly coca ine-nega t ive ur ine specimens (abstinencegroup). Although both groups had similar rates of coca ine-nega t ive ur ine specimens dur ing the fi rs t 3 weeks of the inter-ve n t i on , th e shaping group showed an increase in nega t ive

specimens on escalation of the cont ingency requirement . Thisadded t r ea tment e f fec t was evident dur ing th e la tter 5 weeks ofth e in te rvent ion and tended to be mainta ined across a 12-weekmaintenance t r ea tment . As we had hypothesized, pa r t ic ipants inthe shaping group contac ted th e re inforcer more f requent ly thandid those in the abst inence group.


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SH A PI N G COCA I N E A B STI N EN CE 651601

50"

40-

30

20

10 contingentnoncontingent

42 45 48 51 54 57 60 63 66 69 72 75Number of consecutive urine specimens

Figure 2. Percentage of part ic ipants coca ine abs t inen t on 36 success iveur ine tes t days in the maintenance phase in the two trea tment groups :con t ingen t g roup (vouche r s a nd t a ke -home me tha d one doses for coca ine-negative urine specimens; n = 41), noncon tingen t group (vouchers andtake-home methadone doses independent of urine tes t resul ts ; n = 39).A p p rox im a te ly half of the patients ha d part ic ipa ted in the abs t inence groupan d half ha d participated in the s ha p ing g roup jus t p r io r to the ma in tena ncephase. Data shown here a re raw percentage va lues ; m i s s i n g s pec imens( inc luding those due to dropout) a re t rea ted as pos i t ive .

The present findings extend the body of work on shaping(reinforcement of successive approximations of a final target be-havior ) as a method of substance-abuse treatment. Shaping hasbeen used to increase substance-abuse patients ' completion oftreatment-plan tasks (Iguchi, Belding, Morral, L amb , & H us b and ,1997). Patients received contingent vouchers for counselor-assigned behaviors directed at meeting treatment goals, such asgaining employment. I f the patient did not complete an assignedtask, a less diff icul t task was s ubsti tuted; if the task was completed,a more diff icul t task was assigned. Contingencies were thustailored to each patient 's needs. The shaping procedure was ap-parent ly successful, as patients had significant increases in drug-free urine specimens compared with patients receiving voucherreinforcement of drug-negat ive ur ine spec imens an d with patientsin a standard-care group.

Prior studies have also involved reinforcement of decreases inbiological indicators o f drug use; this ha s been attempted mostfrequent ly with tobacco, using exhaled carbon monoxide (CO) asthe indicator of use. Early studies did not involve shaping in thestrictest sense because th e response requirements never changed;mone tary rewards were given each t ime part icipants reached afixed target of 50% of baseline CO (Sti tzer & Bigelow, 1982;Schmitz, Rhoades, & Grabowski, 1995) or a fixed target of 16 or 8ppm (Sti tzer & Bigelow, 1985). In the lat ter study, i t was notedthat the use of a diff icul t t a rge t (8 p p m) led to fa i lures to contac tthe reinforcer, leading the authors to suggest that such a targetshould not be int roduced abrupt ly. The deve lopment of a s l id ing-scale procedure , in which the magni tude of each reward wasinversely related to the amo unt of CO detected (Sti tzer & Bigelow,1984), led to a study similar to the current one, in which asliding-scale phase was followed by an abstinence-contingencyphase (Sti tzer, Rand, Bigelow, & Mead, 1986). In that study,

Table 5Urine Test Results: Percentage of Drug-Negative Specimens in Maintenance

VariableCocaine nega tive0

M (SEM)Ad j fo r basel ine urineAd j fo r in te rven t ion ur ineOpia te negative 0M (SEM)Ad j fo r basel ine urine

Benzodiazepine negat ive 0M (SEM)Ca nna b i s nega tive 0M (SEM)Alcohol negative*1M (SEM)

C on t ing e n t

3 7 ( 6 )372261(5)669 3 ( 2 )75(6)9 7 ( 1 )

A N O V A a GLIMMIX "G roup G roup G roup Da y

N onc on t ing e n t F p F p F p

21 (4.5) 5.06 .0273 4.71 < .04 1.76 < .017 6.58 < .02 1.63 < .02

58(5 ) 0.31 .57860 . 0.47 .50 1.19 .2187(4) 1.81 .18286(4) 2.66 .10798 (1) 0.33 .566

Group X DayF P

1.29 .121.11 .30

0.97 .52

Note . Genera l ized l inear mixed model (GLIM MIX) is an SAS macro tha t ana lyzes d ichotom ous repea ted m easures with miss ing da tapoints by invokingth e SAS procedure MIXED with a logit l ink. A N O VA = a na l ys i s o f var iance , adj = adjus ted .* A N O V A degrees of freedom are 1 and 78; mis s ing ur ine samples were considered pos i t ive fo r coca ine an d opia tes for A N OVA s . b GLIMMIX degreesof freedom for group are 1 and 73 and for day and Group x Day, 35 and 2,410. Adjus ted (Adj) percentages a re from GLIMMIX models; they appear lowbecause they c ontrol for intervention -phase contingenc y, dropout, poor a t tendance, and e i ther basel ine urin e sample tes ts or intervention urine tes ts ; theyare presented here for intergroup comparisons ra ther than as absolute ind ica tors of performance. GLIMMIX models were not fitted for benzodiazepines ,cannabis, or alcohol because low rates of use led to underd ispe rs ion ( lack of varia t ion) in the da ta . c Urine specimens . d Breath specimens .


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652 PRESTON, UMBRICHT, WONG, AND EPSTEINTable 6Self-Reported Cocaine an d Heroine Use, Craving, Lifestyle Changes,an d Criminal Activity Maintenance

Mixed regressionGroup Group Week Group X Week

Variable Contingent Noncontingent F p F pSelf-reported cocaine use"Mean frequency per day:M (SEM)Ad j M (SEM)Mean amount per day (mg)

M (SEM)Ad j M (SEM)Mean dollars spent per dayM (SEM)Ad j M (SEM)Self-reported heroin us e3Mean frequency per dayM (SEM)Ad j M (SEM)

Mean amoun t per day (mg)M (SEM)Ad j M (SEM)Mean dollars spent per dayM (SEM)Ad j M (SEM)Weekly self-report questionnaireCocaine cravingbM (SEM)Ad j M (SEM)Heroin craving5M (SEM)Ad j M (SEM)Lifestyle changes 0M (SEM)Ad j M (SEM)Criminal activities'M (SEM)Ad j M (SEM)

0.27(0.06) 0.41(0.07)0.42(0.09) 0.54(0.09) 1.66 .20 0.92 .61 1.06

0.08(0.02) 0.12(0.03)0.11(0.03) 0.15(0.03) 1.29 .26 0.88 .67 0.950.11(0.03) 0.13(0.04)0.16(0.04) 0.19(0.03) 1.05 .31 1.04 .41 1.400.52(0.14) 0.76(0.26)0.75(0.26) 1.07(0.24) 1.66 .20 0.75 .86 1.251.21(0.15) 1.22(0.15)1.43(0.18) 1.39(0.17) 0.05 .82 1.21 .27 0.691.25(0.18) 1.13(0.15)1.57(0.20) 1.38(0.20) 0.85 .36 0.90 .54 1.314.14(0.42) 4.23(0.43)3.90 (0.46) 3.62(0.43) 0.36 .55 0.90 .54 0.350.03 (0.02) 0.02 (0.02)0.05(0.02) 0.04(0.02) 0.11 .74 0.80 .64 1.06

.3828.5(7.3) 41.9(14.7)42.0(14.4) 35.7(13.9) 0.20 .66 0.97 .52 0.92 .611.86(0.60) 1.59(0.30)4.82(1.80) 3.91(1.71) 0.22 .64 1.09 .33 1.32 < .10

.55

.06

.15

.75

.22

.97

.39Note. Adjusted (Adj) means control for baseline, intervention-phase contingency, dropout, an d poor atten-dance.a Data were available for 80 participants. Degrees of freedom are 1 and 73 for group and 35 and 2,410 for timean d Group X Time. b Data were available for 78 participants. Degrees of freedom are 1 and 71 for groupan d 1 1 and 684 for t ime and Group X Time. Craving wa s rated on a scale of 0-4. c Data were available for 78participants. Degrees of freedom are 1 and 71 for group and 11 and 684 for time and Group X Time. Lifestyle changesare reported as the mean sum of the i tems reported per week. Criminal activities are the mean of the total.

participants' reductions in smoking during the sliding-scale phasepredicted their subsequent ability to abstain. However, all partic-i pan t s in that study were exposed to the sliding scale; there was noabs t inence-only group fo r comparison.We know of only two published studies (prior to this one)i nvo lv ing reinforcement of decreases in biological indicators ofcocaine use. In one of them, the reinforcement was used only as am e a n s to induce abstinence so that withdrawal symptoms could bes tudied; thus, there was no baseline condition and no control group(Evans , Levin, Fischman, & Foltin, 1998). Nonetheless, there wassome suggestion of eff icacy. Nine non-treatment-seeking cocainesmokers earned vouchers for each urine specimen that had adecreased concentration of BZE (compared with the previouslycollected specimen). Of 81 specimens collected, 68% had concen-t ra t ions lower than the previous specimen, 56% had decreases of50% or greater (suggesting no new use since the prior specimen

collection), and 23% of all specimens were negative for BZE.Another study used a sliding scale (monetary reinforcers of $10 or$12 for each successive decrease in the level of BZE and $12 or$15 for each cocaine-negative specimen) in 12 cocaine-dependentmethadone-maintenance patients (Elk et al., 1995). The procedurewas effective; BZE levels significantly decreased and cocaine-negative specimens increased compared with a period of baselinetreatment. Again, there was no abstinence-contingency controlgroup, nor was there a subsequent attempt to introduce anabstinence-only requirement.In our study, those two elementsan abstinence-contingencycontrol group and an elevation of the response requirementenabled the most striking of our findings: The shaping group's rateof cocaine use differed f rom that of the abstinence group onlywhen the response requirement ceased to differ. During the first 3weeks of intervention (the only time when the shaping contingency


11/12

SH A PI N G COCA I N E A B STI N EN CE 653was in effect), part icipants in both groups sharply reduced theirrates of use relative to baseline (Figure 1). On the basis of everyavailable drug-use measure, the two groups were behaving almostidentically. The difference lay in the consequences: For part ici-pants in the shaping group, reductions in cocaine use were rein-forced more frequently (Table 2). In the subsequent 5 weeks ofintervention, when the response requirement for both groups wasabstinence, the former shaping part icipants maintained a higherrate of abstinence than did those for whom the response require-m e n t had been abstinence all along. Even in the ensuing mainte-nance phase, this trend continued (though not to a degree thatreached stat ist ical significance) within each of the new reinforce-ment schedules to which part icipants were rerandomized.

These results are reminiscent of findings from the applied be-havior analysis l i terature on compliance, where i t has been shownthat re inforcement of a high-probabili ty behavior ( i .e . , a behaviorthat part icipants will readily engage in ) increases subsequent com-pliance with a requirement to perform a low-probabili ty behavior(i.e., a behavior that part icipants will not readily engage in ; Mace,Mauro, Boyaj ian, & Eckert, 1997). This "high-p procedure" de-scribes our shaping intervention, which reinforced a behavior( reduc tion of d rug-use f requency) that occurs in nearly all part ic-ipants at the start of a voucher intervention, even if vouchers aregiven noncontingently (Preston et al., 2000).The effectiveness of the high-/? procedure has been interpretedas an example of behavioral momentum, defined by Nevin as theproduc t of response rate an d resistance to change (Nevin, 1992;Ne v i n , Mandell, & Atak, 1983). According to this theory, greaterdensity of reinforcement of a behavior leads to greater resistancefo r the behavior to change, even when the reinforcement schedulechanges (P laud & Gaither, 1996; Plaud , Gaither, & Lawrence,1997). The aptness of the "momentum" metaphor ha s been ques-t ioned (Houl ihan & Brandon, 1996), but our results at least add tothe body of data to which i t seems applicable.

The maintenance-phase re sul t s ar e encouraging . Cont ingencymanag e me n t is intended for use in real-world clinical set t ings, an done of i ts most effective variants is the escalating-reinforcementprocedure used in the intervention phase (and in many of our others tud ies)but thi s var iant has the inherent l imi ta t ion of e scala t ingcost. O ur maintenance-phase results show that even in patientswho have been exposed to escalating reinforcement, abstinencecan be at least part ly sustained by a more modest schedule ofnonescalating reinforcement ( i .e . , fixed-amount vouchers and take-home doses). Comparable findings have been reported by Higginset al. (1994), who successfully followed an escalating schedulewith one in which each negative urine specimen was reinforcedwith a state lottery t icket. Nonescalating schedules could havepractical applications fo r patients w ho return to frequent cocaineuse w h e n an escala ting cont ingency is d iscont inued .The present study had a number of l imitat ions. First , there wasno nonvoucher or noncont ingent -voucher cont rol group wi thwh i ch to compare th e shaping and abstinence groups. Neverthe-less, patients in both groups clearly improved with the onset ofcont ingency management , an d (wi th du e acknowledgement of thel imitat ions of historical controls) their improvements appearedgreater than those of noncontingent-voucher groups in our otherstudies (Silverman et al., 1996, 1998). Second, patients weremainta ined on re la t ive ly low m ethadone doses; th e rates of heroinand cocaine use might have been lower had methadone doses beenhigher or indiv idua lized. Finally, the overall level of improvemen t

may have been reduced by the delayed delivery of re inforcers andby the short duration of the intervention. Vouchers were given 1da y after urine specimens were collected because of our use of anoutside laboratory to obtain qua nti tat ive urine test results. Delay ofdelivery can weaken the strength of a re inforcer.Overall , shaping (by means of re inforcement of decreases inurine-cocaine metaboli te concentrations) led to more part icipantscontac t ing th e reinforcer and a greater density of reinforcer deliv-er y per participant. When a more stringent response requirementwas introduced, cocaine abstinence was enhanced for part icipantswho had previously been reinforced on the shaping schedule. W econclude that this procedure prepared part icipants for abstinence.Improvements were sustained in a maintenance treatment provid-ing nonescalating reinforcers that were contingent on abstinence.

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Received Ma y 1, 2000Revision received September 26, 2000

Accepted October 8, 2000

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