89 (2007) 330–338www.elsevier.com/locate/schres

Schizophrenia Research

Correlations of functional capacity and neuropsychologicalperformance in older patients with schizophrenia:

Evidence for specificity of relationships?

Margaret M. McClure a,⁎, Christopher R. Bowie a,b, Thomas L. Patterson c,Robert K. Heaton c, Christine Weaver b, Hannah Anderson b, Philip D. Harvey a,b

a Department of Veterans Affairs, VISN-3 Mental Illness Research, Education, and Clinical Center (MIRECC),130 West Kingsbridge Road Bronx, NY 10468, USA

b Department of Psychiatry, Mt. Sinai School of Medicine, USAc Department of Psychiatry, UCSD Medical Center, USA

Received 31 May 2006; received in revised form 24 July 2006; accepted 31 July 2006Available online 18 September 2006

Abstract

Background: Neuropsychological (NP) performance is a consistent correlate of everyday functioning in schizophrenia, but it isunclear whether relationships between individual NP ability areas and domains of everyday functioning are general or specific.Assessments of real-world everyday functioning may be influenced by environmental and social factors (e.g., social security,disability status, opportunities and restrictions in living situations). This study examined the specificity of the relationships betweendifferent NP abilities and performance-based measures of social and living skills.Methods: 181 ambulatory older (ageN50) patients with schizophrenia were examined with NP tests measuring episodic andworking memory, executive functioning, verbal fluency, and processing speed. All subjects performed tasks examining social(Social Skills Performance Assessment: SSPA) and everyday living (UCSD Performance Based Skills Assessment: UPSA) skills.Results: Using canonical analysis, the NP variables were used to predict the functional capacity measures. The analysis found that37% of the variance in the functional capacity and NP measures was shared, X2 (54)=106.29, pb .001. Two canonical rootsdescribed the cognitive variables and the roots were differentially associated with everyday living and social skills. The rootloading on processing speed, episodic memory, and executive functions were associated with UPSA scores, while the root loadingon working and episodic memory and verbal fluency were associated most strongly with social competence.Implications: Social and everyday living skills deficits in patients with schizophrenia may reflect generally independent domains offunctional outcome, linked through cognitive performance. The data suggest that somewhat different cognitive processes are associatedwiththese two domains of functional capacity, although there appears to be some overlap, which may be due to the nature of the NP testsemployed.© 2006 Elsevier B.V. All rights reserved.

Keywords: Neuropsychology; Everyday living skills; Factor analysis; Social skills; Functional capacity

⁎ Corresponding author. Tel.: +1 718 584 9000x3844; fax: +1 718 364 3576.E-mail address: Margaret.McNamara@mssn.edu (M.M. McClure).

0920-9964/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.schres.2006.07.024

331M.M. McClure et al. / Schizophrenia Research 89 (2007) 330–338

1. Introduction

An important personal and social cost of schizophrenicillness is its effect on occupational and social functioning.Improving the functional outcome of individuals withschizophrenia remains an elusive target, even after decadesof research on interventions specifically addressing thisissue. Numerous studies (for a recent review, see McGurkand Meuser, 2004) have demonstrated that positivesymptoms are a poor predictor of functional outcome.Thus, although pharmacological interventions have oftensucceeded in treating the positive symptoms of schizo-phrenia (Marder and Meibach, 1994), there has been afailure to translate symptom reduction into improved workand social functioning (McGurk et al., 2003; Green, 1996;Green et al., 2000). Negative and cognitive symptoms, onthe other hand, appear to be better predictors of socialcompetence and community functioning (McGurk andMeuser, 2004; Green, 1996) and also, unfortunately, areless well treated by current pharmacological interventions.Although both contribute to factors such as the perfor-mance of daily living tasks and the acquisition andmaintenance of community employment (Revheim et al.,2006), negative and cognitive symptoms are most likelyseparable domains exerting independent influences onperformance (Bowie et al., 2006; Harvey et al., 2006).

Neurocognitive deficits are a well-established featureof schizophrenia and cognitive functioning has repeatedlybeen shown to be the best predictor of communityfunctioning following treatment (Bowie et al., 2006;Kurtz et al., 2005; Green et al., 2004; Lowery et al., 2003;Harvey et al., 1998). A question that arises, based onGreen's (1996) initial suggestions, is whether specificaspects of cognitive functioning have relationships withspecific domains of functional outcomes, such asbehaviors involved in employment, independent living,and social interactions. For example, Green's firstevaluation of the data suggested that secondary verbalmemory, or episodic memory, was related to communityfunctioning, regardless of the outcome measure utilized,as well as to both social problem solving and social skillacquisition. Immediate verbal memory was consistentlyrelated to social skill acquisition but was less consistentlyrelated to social problem solving. Vigilance, as measuredby continuous performance tests, was repeatedly relatedto the acquisition of social skills, was unrelated tocommunity functioning, andwas related to social problemsolving in half of the studies that Green examined.Executive functioning, as measured by card sorting tests,was consistently related to community outcome but wasinconsistently related to social skill acquisition and wasunrelated to social problem solving.

Results of studies evaluating these associations havebeen mixed since this first publication. For instance,Harvey et al. (1997), studying institutionalized patients,could not distinguish between the cognitive predictors ofsocial and self-care functions. Evans et al. (2003)examined the relationship between neuropsychologicalperformance, symptom severity, and a performance-basedmeasure of functional capacity, the Direct Assessment ofFunctional Status (DAFS; Loewenstein et al., 1989). Theyfound that general cognitive ability, not specific abilitydomains, strongly predicted DAFS performance, evenafter controlling for demographic differences and nega-tive symptoms. Thus, theywere unable to find evidence ofspecific relationships between aspects of NP performanceand everyday living skills. Gold et al. (2002) found thatperformance on a comprehensive neuropsychologicalbattery did not improve on the ability of a single briefmeasure, WAIS digit symbol, for the prediction ofemployment outcomes. Revheim et al. (2006) foundthat negative symptoms, processing speed, verbal mem-ory, and working memory scores all correlated with real-world daily problem-solving skills as measured by theIndependent Living Scale (ILS-PB; Loeb, 1996). Evanset al. (2004) examined the relationship between workbehavior, as measured by the Work Behavior Inventory(WBI; Bryson et al., 1997), neuropsychological abilityand symptom severity, in individuals with schizophreniain one of several employment programs. They found thatbetter verbal learning andmemory, executive functioning,and processing speed were related to better employmentoutcomes, as measured by factors such as the number ofhours worked, at a 4-month follow-up. McGurk et al.(2003) found that executive functioning, verbal learning,psychomotor speed, and attention all predicted jobperformance, but only when individuals were providedwith appropriate levels of support.

Thus, it is not clear that there are specific relationshipsbetween cognitive ability domains and everyday func-tioning. In order for differential correlational relationshipsbetween cognitive ability domains and aspects ofeveryday functioning to be identified, it must be thecase that both the predictor (cognitive) and criterion(functioning) domains contain variables that are separablefrom each other. In the area of cognition, the results offactor analytic studies are somewhat mixed, with somestudies suggesting that a single “general ability” domainmay be among the best fitting models for data based onNP performance, and other studies finding multidimen-sional solutions. In the area of functional outcomes, thereis much less formal statistical information available, but itis clear that many patients with schizophrenia are disabledacross several domains of functioning simultaneously.

332 M.M. McClure et al. / Schizophrenia Research 89 (2007) 330–338

Amajor issue in the interpretation of studies correlatingcognitive performance and everyday living skills is thatfactors other than ability or competence (what one can do)can impact on real-world performance (what one does).The studies cited above, and contained in the reviewarticles by Green (1996) and Green et al. (2000), present amix of measurement of everyday living skills in thecommunity and assessment of skills competence measuredin rehabilitation settings (see, for example, Kern et al.,1992). Directly relevant to this point is the recent finding byRosenheck et al (2006) indicating that while cognitiveperformance was correlated with occupational status inpeople with schizophrenia, racial and disability status had amuch larger impact. Thus, real-world performance isinfluenced by a host of variables that may have little to dowith individual differences in cognitive ability. In order torelate performance on cognitive tests to specific functionalability, use of a performance-based approach may bepreferable because it is not as subject to influence by otherenvironmental factors. Further, previous studies have oftenused correlational techniques that did not simultaneouslyconsider the range of NP skills, on the one hand, and therange of everyday living and social skills, on the other.

This paper reports the results of a study using aneuropsychological assessment that was designed tocapture ability areas relevant to everyday living and socialskills and multidimensional performance-based measuresof everyday living skills and social competence. In sodoing, we examined the relationship between specificcognitive abilities and specific aspects of the functionalcompetencies that may underlie everyday outcomes. Usingcanonical analysis, we examined the simultaneous relation-ships between performance on NP tests and the perfor-mance-based assessment of social and everyday livingskills. By using a broad assessment of functional capacitythat was specifically developed for the population westudied (older community dwelling people with schizo-phrenia), we hoped to perform an ecologically validassessment of skills competence and to avoid theconfounds of other environmental factors that mightinfluence the everyday deployment of functional skills.

2. Methods

2.1. Subjects

Subjects in this study were older, community dwellingschizophrenia patients enrolled in a longitudinal study ofthe course of cognitive and functional status. The long-term goal of this project is to examine the course andcorrelates of change in functional status among older,ambulatory schizophrenia patients. Exclusion criteria

included a primary DSM-IVAxis I diagnosis other thanschizophrenia or schizoaffective disorder, Mini-MentalStatus Examination score below 18, or any degenerativedisease that might confound the assessment of cognitivefunctioning. All subjects were in outpatient treatment atthe time of recruitment at a VA, New York state, oracademic research site. Outpatient status was defined asliving outside of any institutional setting, including anursing home. Study subjects were also required to haveevidence of continued illness at the time of recruitment, asevidenced by meeting at least one of three criteria: (1) aninpatient admission for psychosis in the past 2 years; (2)an emergency room visit for psychosis in the past 2 years;or (3) a score on at least one of the PANSS positivesymptoms items relating to delusions, hallucinations, orconceptual disorganization of 4 (moderate) or more at thetime of baseline assessment. All subjects signed a writteninformed consent form approved by the institutionalreview board at each research site after the testingprocedures were fully explained.

All subjects met diagnostic criteria for schizophreniaor schizoaffective disorder (DSM-IV). The Comprehen-sive Assessment of Symptoms and History (CASH) wascompleted by a trained research assistant and diagnosiswas confirmed with a senior clinician. Trained raters ateach site performed all testing. Patients were onlyenrolled in this part of the study if they were receivingcase management services and actively involved inpsychiatric rehabilitation services. All patients werereceiving treatment with second-generation antipsychot-ic medications.

2.2. Measures

All subjects completed the test battery in a fixedorder. Screening measures were of global cognition withthe Mini-Mental State Examination (MMSE; Folsteinet al., 1975) and estimated premorbid functioning withthe Wide Range Achievement Test, 3rd edition(WRAT3; Jastak and Wilkinson, 1994) RecognitionReading subtest. These measures were followed byfunctional skills assessment, a cognitive test battery, anda symptom interview. All raters received extensivetraining in performing all of the assessments and every3 months their performance was re-evaluated throughre-rating of training tapes, dual-ratings of the functionalstatus measures with the second author, and qualityassurance assessments of all testing. These raters weretrained to adequate reliability on symptom ratings withtwo full days of training, four standardized videotapesand in-person interviews that yielded Intraclass Corre-lation Coefficients from .86 to .92.

Table 1Demographic data, performance, and ratings

Domain Variable Mean S.D. Range

Demographic Age 58.4 7.3 50–87Education 12.5 2.4 5–18Gender (% male) 71Ethnicity (% Caucasian) 68MMSE 27.6 3.2 21–30

Symptom PANSS Positive Sx Total 13.6 4.4 7–31PANSS Negative Sx Total 14.0 4.8 7–28PANSS General Sx Total 27.5 7.4 16–48

Performance WCST total errors (scaled score) 74.2 14.9 11–114TMT part A 65.9 33.2 24–240TMT part B 157.2 59.8 53–240Digit span forward 9.0 2.3 2–14Digit span backward 5.3 2.6 0–14Digit symbol 34.4 15.5 3–85LNS 6.6 4.1 2–19RAVLT learning 33.9 11.7 12–63Animal naming 16.4 5.8 4–33WRAT-3 reading scores (raw) 46.78 6.5 33–67

Functional skills (UPSA) Comprehension/planning 21.0 4.2 6–25Financial skills 7.9 2.6 0–11Communication 6.1 2.0 0–17Mobility 4.9 1.6 0–10

Social Skills PerformanceAssessment (SSPA)

Total score 3.8 2.0 2.0–4.9

NP performance scores are all raw scores. SSPA is averaged across two scenarios.

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2.3. Performance-based measures of functional capacity

2.3.1. UCSD performance-based skills assessmentbattery (UPSA)

The UPSA (Patterson et al., 2001a) is designed todirectly assess functional skills competence among theseverely mentally ill. This test is designed for olderoutpatients and measures performance in a number ofdomains of everyday functioning through the use of propsand standardized skills performance situations. The

Table 2Intercorrelations of functional and cognitive variables

NP Variables Functional capacity measures

Comprehension planning Financial m

WCST errors .27 .32Trail-making part A .29 .23Trail-making part B .21 .34Digit span forward .22 .34Digit span backward .24 .33LNS .28 .22Digit symbol .28 .32RAVLT learning .29 .39Animal fluency .16 .15

N=181.Correlations of r≥ .16 are significant at pb .05 two-tailed.

Comprehension/planning domain measures the patient'sability to comprehend written material that describerecreational outings and then plan the activities and listappropriate items necessary to bring to the outings. In thefinance domain, the patient must count out given amountsfrom real currency, make change and fill out a check to paya utility bill. The Communication domain involves a seriesof role-play situations that require the patient to makeemergency calls, call directory assistance to request atelephone number, call the number, and then reschedule a

anagement Communication Mobility SSPA

.31 .25 .20

.36 .40 .20

.39 .33 .24

.34 .11 .37

.37 .16 .36

.13 .16 .34

.37 .37 .19

.28 .25 .35

.19 .15 .36

334 M.M. McClure et al. / Schizophrenia Research 89 (2007) 330–338

medical appointment. In the Transportation/mobilitydomain, patients use information from bus schedules andmaps to determine appropriate fare, state telephonenumbers to answer relevant questions, decide which mapto use to get to a certain location, and determine the appro-priate route and transfers to reach a destination. We did notuse the household maintenance subtest because testing atfield sites precluded the use of the analog pantry that isrequired for this test.We then transformed the scores so thateach subscale had a maximum score of 25, so that totalscores would be consistent with earlier presentations of theUPSAwith five subscales and a total possible score of 20for each subscale. For the purposes of these analyses,we used each of the total scores for these four domainsseparately.

2.3.2. Social Skills Performance Assessment (SSPA)The SSPA (Patterson et al., 2001b) is a social role-play

task in which the subject participates in two 3-min role-plays presenting selected social problem situations actedout between an interviewer and participant andaudiotaped for subsequent centralized scoring. Scene 1:A 3-min interaction inwhich the subject plays the role of atenant meeting a new neighbor (interviewer). Scene 2: A3-min interaction in which the subject plays the role of atenant calling the landlord (interviewer) regarding a leakthat has gone unrepaired after a previous complaint.Interviewers audiotaped the interviews but did not scorethe interviews themselves. Scoring was performed byother trained raters who were blind to subject identity andresults of other assessments. Each scene was replayedfrom the tape recording and scored on a graduated scalefrom 1 (low) to 5 (high) in 8 categories: interest; fluency;clarity; focus; social appropriateness; negotiation ability;persistence; overall conversation. Overall performancewas calculated by summing the averaged ratings fromeach role-play, leading to an overall score that could rangefrom 2 to 10. Inter-rater reliability of scoring theinstrument was based on a 20% overlap in ratings, andthe average ICC for scores for each of the 8 categories wasfound to be .89. Previous data on the practice effects of theSSPA indicated that the test–retest reliability of the SSPAwas .91 and that there was no significant change inperformance at a 4-week retest assessment in eitherhealthy controls or patients with schizophrenia.

2.4. Cognitive assessments

Patients completed a comprehensive assessment of thecognitive ability areas previously shown to be mostconsistently correlated with both real-world and perfor-mance-based measures of functional skills, including

attention, motor skills, verbal learning and memory, verbalfluency, and several aspects of executive functioning. Forthe analyses in the present study, scores from the followingmeasures were employed: animal naming,Wisconsin CardSortingTest 64-card computerized version (WCST;Heatonet al., 1993) total errors, Trail-making Test (Reitan andWolfson, 1993) Parts A and B, Rey Auditory VerbalLearning Test (RAVLT; Spreen and Strauss, 1998) learningtrials 1–5, and Wechsler Adult Intelligence Scale, 3rd ed.(WAIS-III; Wechsler, 1997) digit symbol, digit span andletter–number sequencing subtests. Thus, measures ofexecutive functioning, episodicmemory,workingmemory,processing speed, attention, and verbal skills wereincluded. We also used scores on the Wide-RangeAchievement Test 3rd ed. (WRAT-3) word recognitionreading subtest to estimate potential influences of pre-morbid academic achievement.

2.5. Statistical Analyses

The main analytic plan was comprised of canonicalanalysis. In canonical analysis, a set of predictorvariables are examined for their joint relationship witha set of criterion variables. This analysis yields factors,referred to as “canonical roots”, on which the variableson each side of the equation manifest loadings that areanalogous to factor loadings in a principal componentsanalysis. Variables on each side of their equation can beevaluated in terms of their loadings on the different rootsfrom that side of the equation and correlations with thecanonical roots on the other side of the equation.

Overall statistical significance of the predictor set canbe evaluated with the same procedure that is applied toMultivariate Analysis of Variance (MANOVA). Further,while there are no specific tests that are applied for thedifference in factor loadings between canonical roots,these loadings are analogous to correlation coefficientsand can be tested with Fisher's z-tests for the signifi-cance of the difference between correlation coefficients.Finally, if differential relationships between canonicalroots on the two sides of the equation are detected, thesecan be followed up by linear regression analyses.

3. Results

181 patients completed all of the baseline assess-ments without any missing data. Demographic data arepresented in Table 1, along with group means for theUPSA and SSPA total scores, and performance on theNP tests. Bivariate Pearson correlations between the NPand functional capacity variables are presented inTable 2.

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3.1. Overall canonical results

The overall results of the canonical analysis werestatistically significant, Canonical R=.64, X2 (75)=147.75, pb .001, indicating that the two sets of variableswere quite strongly related to each other. Two canonicalroots were extracted from the right-side (i.e., NP) variablesand the loadings for those roots are presented in Table 3. Asingle canonical root was extracted from the left sidevariables, such that subsequent analyses examining therelationships between the right side roots and the functionalcapacity variables were performed with the 5 individualfunctional capacity measures. Correlations between thesefunctional capacity measures and the two canonical rootsare presented in the bottom of Table 3.As can be seen in thetable, WCST categories loaded on both roots, as did totallearning on the RAVLT. Measures of processing speedloaded more strongly on root 1 than root 2, while attention/working memory measures loaded more strongly on root 2than root 1. Verbal fluency, often referred to as a processingspeed measure but also tapping the ability to searchsemantic memory and retrieve words and generate spon-taneous verbal output, loaded primarily on the same root asthe working memory measures. As can be seen in thebottom of the table, the UPSA variables tended to loadmore consistently on root 1 than 2, while the SSPA totalscore was more strongly related to root 2 than root 1.

Table 3Neuropsychological canonical roots and correlations of canonicalroots with functional capacity measures

Right side canonical roots

Variable Root 1 Root 2WCST categories 0.28 0.27Trail-making part A −0.74 −0.23Trail-making part B −0.55 −0.38Digit span forward 0.28 0.46Digit span backward 0.24 0.66Digit symbol 0.85 0.11Letter–number sequencing −0.03 0.75RAVLT total learning 0.42 0.48Animal fluency 0.10 0.70Eigenvalue 2.46 2.31

Correlations with functional capacity measures

Functional capacity variable Canonical rootscorrelations

zdiff p

UPSA Root 1 Root 2Comprehension/planning .45 .24 1.98 .024Financial management .47 .35 0.94 .173Communication .38 .31 0.45 .130Mobility .53 .10 3.09 .001

SSPATotal Score .27 .50 2.23 .011

In order to examine the possible differences in corre-lations across the two skills competence measures, sta-tistical tests were calculated for the significance of thedifference in the loadings of the two NP roots on the twodomains of functional capacity. Using Fisher's r to ztransformation, tests of the differences in the size of theloadings were performed and the results are presented inTable 3. As can be seen in the table, for Comprehension/planning and mobility, the loadings of canonical root 1were significantly higher than for root 2, while therewere no differences in the loadings for finance andcomprehension and planning. For SSPA performance,the loading for canonical root 2 was significantly higherthan for 1. Thus, while not consistent across all of thecomponents of the UPSA, there appear to be differencesin the importance of the canonical roots for theprediction of everyday living and social skills.

3.2. Partial Correlation Analysis

Because the functional capacity measures loaded on asingle canonical root, the possibility arises that thesevariables are not “truly” different from each other despitethe differential canonical loadings found in the previousanalyses. Since cognitive variables shared a considerableamount of joint variance with these two domains offunctional capacity, it could mean that the apparentlyunitary relationship between everyday living and socialskills is influenced by joint correlations with NPperformance. To investigate this possibility, partial correla-tionswere computed between the 4UPSAdomains and theSSPA total score, controlling for the two canonical rootsreflecting NP performance. Prior to partial correlations, thecorrelations between the SSPA and the UPSA domainsranged from a low of r=.39 (communication) to a high ofr=.60 (mobility), all p'sb .05. When the cognitiveperformance was controlled with partial correlationanalysis, the correlationswere reduced in their size, rangingfrom a low of .18 (communication) to a high of .37(mobility), all p'sb .05. Thus, global aspects of NPperformance may increase the observed correlationsbetween different dimensions of functional capacity.

3.3. Regression Analyses

As the analyses above suggested the possibility ofdifferential predictive relationships between aspects of NPperformance and measures of everyday living skills andsocial competence, the UPSA variables were combinedinto a total score and then that score and the SSPA totalscore were examined with regression analyses. Thepredictors used for each analysis were the variables with

336 M.M. McClure et al. / Schizophrenia Research 89 (2007) 330–338

the highest loading on the root most strongly associatedwith the everyday living and social skillsmeasures. In theseexploratory analyses, therefore, the items that loaded oncanonical root 1, theWCST, theRAVLTand the processingspeed measures, were used to determine the varianceaccounted for in UPSA total scores and the items thatloaded on canonical root 2, the WCST, RAVLT, workingmemory, and verbal fluencymeasures, were used to predictthe SSPA total scores.

These analyses were performed with simultaneousentry analysis, in order to confirm an overall associationbetween the functional capacity and NP performancemeasures, followed by stepwise regressions designed toidentify the contributions of each NP variable. For theUPSA, the overall simultaneous regression was signifi-cant, F(5,176)=12.34, pb .001. When the analysis wasrepeated with a stepwise procedure, trail-making part Aentered the equation first, accounting for 17% of thevariance ( pb .001), following by RAVLT total learning,accounting for an additional 6%of the variance ( pb .001),following by trail-making part B, which accounted for anadditional 3% of the variance ( pb .001). Thus, a total of26% of the variance in UPSA total scores was accountedfor by three different predictor variables that loaded oncanonical root 1. For the SSPA total scores, the overallregression was also significant, F(6,175)=5.04), pb .001.Stepwise regressions found that digit span forwardaccounted for 10% of the variance in SSPA scores( pb .001), followed by animal fluency, which accountedfor an additional 6% of the variance ( pb .001), andRAVLT total learning, which accounted for an additional3% of the variance ( pb .005). Thus, 19% of the variancein SSPA performance was accounted for by three differentpredictor variables associated with canonical root 2, oneof which also accounted for significant variance in UPSAscores.

4. Discussion

The purpose of the present study was to examine therelationships among NP performance and indices offunctional capacity in schizophrenia patients. The resultssupport previous work that found NP performance to beconsistently correlated with performance-based measuresof skills required for everyday functioning.We also foundthat performance-based measures of functional capacityand NP performance share somewhat more variance thanprevious studies of real-world outcomes and NP perfor-mance have revealed. Our data further suggest thepossibility that social and everyday living skills compe-tence may have different NP correlates. Specifically, thetwo canonical roots had significantly different loadings on

social and everyday living skills. Further, the variablesthat most strongly loaded on the two canonical rootsextracted from the NP performance data were correlatedwith scores on the performance-based measures of socialand everyday living skills. Our findings also suggest,however, that the two skills competence measures arerelated to each other and that this correlation may also bemediated by their joint relationship with NP performance.

This study has several limitations, many shared withother similar studies. The ratings of functional capacitycome from psychometrically sound measures, though, likeneuropsychological tests, they are performance-based andrequire cognitive skills and motivation. This raises thepotential for measurement artifact in predicting perfor-mance, in that scores could be influenced by factors otherthan “true” functional ability. For example, illness-relatedvariables such as premorbid functioning could have a jointinfluence on both sets of measures. Patients with poorpremorbid functional or an earlier age of onset may havenever developed certain skills that are previously attained,but poorly performed, by patients with a later age of onset.Our statistical techniques are descriptive in nature and thepurpose of this studywas exploratory. One finding of directrelevance to this is the result that verbal fluency loaded on acanonical root reflecting working memory, rather thanprocessing speed as detected in previous factor analyses(Gladsjo et al., 2004). However, factor analyses of NPperformance in schizophrenia often yield different resultsacross studies (see, for example, Keefe et al. (2006a)). Ourpatients are older and ambulatory, and it is not clear howthese results would apply to younger or more (or less)severely ill patients. Furthermore, the NP test battery wasrelatively brief. A longer batterywithmultiple tasks of eachability domainmay have revealedmore (andmore specific)canonical roots, which may have altered the overallpredictability of the functional capacity measures.

The evidence in this study for specific relationshipsbetween different NP ability areas and different aspects offunctional capacity is moderate and requires replication.While some differential correlations between NP abilityareas and aspects of functional outcomes (verbal skillsand working memory relating to social skills whileprocessing speed relates to everyday living skills), therewas considerable overlap in the loadings of multipleaspects of cognitive functioning (e.g., episodic verbalmemory and executive functioning). This may, however,be due to the overlapping nature of NP tests in general,where many different demands are placed on individualsperforming any specific test. Further, the performance-based measures of functional capacity loaded on a singlefactor, meaning that discovering differential predictors ofthese domains of functional capacity may be a challenge.

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The joint relationship with NP performance may wellunderlie the apparent single dimension of functionaloutcomes because controlling for the influence of NPperformance notably reduces this correlation. This findinghighlights the importance of NP performance in theprediction of functional outcomes. Our results may alsosuggest that, since performance on these differentdimensions of functional capacity is highly intercorre-lated, it may be possible to develop fairly brief assess-ments of functional outcomes, much like abbreviatedcognitive assessments have recently been developed(Keefe et al., 2006b; Velligan et al., 2004).

Acknowledgements

This research was supported by NIMH Grant NumberMH 63116 to Dr. Harvey, the Mt. Sinai Silvio ConteNeuroscience Center (NIMH MH 36692; KL Davis PI)and the VAVISN 3 MIRECC.

This research was also supported by the Mt. SinaiSilvio Conte Neuroscience Center (NIMH MH 66392;KL Davis PI).

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