Development and assessment of the constipation-related disability scale

Development and assessment of the constipation-relateddisability scaleS. L. Hart*, J. J. Albiani*, C. J. Crangle*, L. A. Torbit* & M. G. Varma�

*Department of Psychology, RyersonUniversity, Toronto, ON, Canada.�Section of Colorectal Surgery,Department of Surgery, Universityof California San Francisco,San Francisco, CA, USA.

Correspondence to:Dr S. L. Hart, 350 Victoria Street,Toronto, ON M5B 2K3, Canada.E-mail: [email protected]

Publication dataSubmitted 9 June 2011First decision 22 July 2011Resubmitted 10 October 2011Accepted 10 October 2011EV Pub Online 17 November 2011

SUMMARY

BackgroundChronic constipation is associated with impaired quality of life and physicaldiscomfort. Although inability to engage in day-to-day activities has beensignificantly associated with psychological distress, limited research hasexamined this relationship in constipated samples.

AimTo develop and validate the Constipation-Related Disability Scale (CRDS),which assesses the extent of disability caused by constipation.

MethodsA total of 240 constipated participants and 103 healthy controls completedthe CRDS. Reliability was measured with Cronbach’s coefficient alpha andtest–retest reliability was assessed with intraclass correlation coefficients.Convergent, divergent and predictive validity were assessed.

ResultsComponent and factor analyses were used to derive two factors:Work ⁄ Leisure Activities and Activities of Daily Living, as well as a totalCRDS score. Good reliability was found, with alphas ‡0.87 and intraclasscorrelation coefficients ‡0.85. All scales were negatively correlated with thephysical health subscales of the SF-36 (P < 0.001) and were not significantlycorrelated with the Epworth Sleepiness Scale and Social Desirability Scale,providing support for convergent and divergent validity, respectively. Evi-dence of predictive validity was supported by associations between the totalCRDS with number of physician visits per year (P < 0.01), missed work inthe last year (odds ratio [OR] = 1.11, 95% confidence interval [CI] = 1.06–1.19, P < 0.001) and ER visits in the last year (OR = 1.08, 95% CI = 1.00–1.16, P < 0.05).

ConclusionsThe Constipation-Related Disability Scale is the first instrument thatassesses the impact of constipation on daily activities. There is evidence ofstrong reliability and validity of the instrument.

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ª 2011 Blackwell Publishing Ltd 183

doi:10.1111/j.1365-2036.2011.04910.x

Alimentary Pharmacology and Therapeutics

INTRODUCTIONBroadly defined, constipation is characterised by persis-tently difficult or infrequent (i.e. less than three timesper week) defecation, and includes symptoms such asstraining to defecate, discomfort and sensations ofincomplete evacuation.1 Constipation is a highly preva-lent condition, with estimates indicating that approxi-mately 10–15% of the general population in the UnitedStates, Canada and the United Kingdom are afflicted.1–4

Furthermore, prevalence rates of chronic constipation aresubstantially higher among women and older adults, esti-mated at 21% and 30–40%, respectively.5–7

Constipation is often perceived as a relatively benigncondition that can be ameliorated with minimal inter-vention, however, chronic constipation is associated withseveral complications that can range from mild to severedisability and require medical intervention. Self-reportsindicate that the majority of patients experiencingchronic constipation consider their constipation to be asomewhat, very, or extremely severe medical conditionand commonly report symptoms such as gas, bloating,abdominal pain and discomfort, rectal pain and the sud-den urge to defecate.8 Such symptoms have been shownto negatively impact the daily activities, physical andemotional well-being, work ⁄ school productivity, lifestyle,social and personal functioning, and overall quality oflife (QOL) of constipated individuals.8, 9 For a subset ofthese patients, symptoms can be severe enough to causework or school absenteeism.8

Although the symptoms and outcomes of chronicconstipation have been relatively well documented, littleis known about the impact of constipation on disability.For this study, we utilised the World Health Organiza-tion’s International Classification of Functioning, Disabil-ity, and Health (WHO-ICF) definition of disability:Impairments in body function ⁄ structure leading to activ-ity limitations and participation restriction.10 Simply sta-ted, disability is defined as difficulty in performing one’sday-to-day activities. Although related, QOL is well-dif-ferentiated from disability; the WHO-ICF has definedQOL as ‘an individual’s perceptions of health andhealth-related domains of well-being’.10

Currently, the majority of our knowledge of restric-tion in day-to-day activities for those with constipationis based on case reports and clinical experience andhas yet to be quantified.11 Disability research con-ducted on other populations with chronic medical ill-ness shows that increased ability to perform activitiesof daily life (ADLs) is correlated with better quality oflife.12–14 Furthermore, decreased patient ability to per-

form ADLs has been linked to increased psychologicaldistress.15

Given these associations, a disease-specific measure isneeded to assess the impact of constipation on ADLs.We developed the Constipation-Related Disability Scale(CRDS) to capture and quantify the true extent and spe-cific areas of difficulty present within a patient’s life dueto constipation, and assessed the reliability and validityof the measure.

MATERIALS AND METHODSThe CRDS was developed and validated in conjunctionwith the Constipation Severity Instrument (CSI)16 andthe Constipation-Related Quality of Life (CRQOL) mea-sures.17 Although beyond the scope of this article, theCSI provides an assessment of constipation frequency,severity, and bother as well as an assessment of constipa-tion subtypes, whereas the CRQOL provides a compre-hensive assessment of the impact of constipation ondaily life in both clinic and community samples of con-stipated individuals. Therefore, these instruments, as wellas the CRDS, provide descriptive information that otherpublished instruments do not (e.g. the Patient Assess-ment of Constipation Symptoms and PAC–QOL).18, 19

The University of California, San Francisco (UCSF)Committee on Human Research approved all studyprocedures.

Sample and procedureParticipants (N = 240) were recruited from either a clinicsetting or the community. Patients within the clinic sam-ple (n = 142) were seen in the UCSF Center for PelvicPhysiology; eligibility and referral to the study was basedon their clinic evaluation. The community sample(n = 98) consisted of constipated patients who respondedto advertisements for a study about bowel habits. Toconfirm symptoms of constipation among the commu-nity sample, screening items for constipation wereadministered via telephone which asked if subjects expe-rienced hard stools, infrequent bowel movements, unsuc-cessful attempts to evacuate stool, feelings of incompleteevacuation, need to strain, abdominal bloating and aneed for aids, such as laxatives or enemas. In both sam-ples, eligible subjects were at least 18 years of age, ableto speak and read English, and had experienced symp-toms of constipation for at least 6 months. Participantswere excluded from the study if they experienced symp-toms of faecal incontinence. Consented participants com-pleted a packet of self-report measures and received a$25 gift card upon completion. Ninety participants with

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constipation from both the clinic and community sam-ples also partook in test–retest procedures, whichrequired completing identical questionnaires approxi-mately 2 weeks later.

To examine the discriminant validity of the CRDS,the instrument was also administered to a sample ofhealthy volunteers (n = 103). Healthy volunteers wererecruited via advertisements and two one-day recruit-ment sessions set up in a public area. To be eligible, thehealthy subjects had to be at least 18 years of age andable to speak and read English. Participants wereexcluded if they had any medical conditions for whichthey regularly saw a health care provider. As describedin the validation paper for the CSI,16 which used thesame sample, healthy volunteers reported very low scoreson all constipation severity subscales. Moreover, theirCSI scores were significantly lower and well-differenti-ated from that of the constipated sample.

Developing a preliminary Constipation-RelatedDisability Scale (CRDS)When considering how to assess constipation-related dis-ability, we examined the literature to see whether or notany relevant bowel-related disability measures existed.Because none were found, we conducted a search for dis-ability measures developed with other medically ill popu-lations. Consequently, we drew upon items from theValued Life Activities (VLA) disability scale20 because ofthe breadth of functional domains captured in the mea-sure and the applicability of the scale to chronic illness.The VLA disability scale was originally developed as ameasure of functioning in discretionary life activities inrheumatoid arthritis patients21 and has since been adaptedfor systemic lupus erythematosus.20 The VLA items weredeveloped based on Verbrugge and Jette’s Model of Dis-ablement,22 which proposes that disability measurementshould not just include obligatory activities (e.g. hygiene,self care, walking), but also committed activities (e.g.household responsibilities, productive social roles) anddiscretionary activities (e.g. socialising, engaging in leisureand other pleasurable activities). Although developed foranother medical illness, the VLA items effectively cap-tured many of the activities that patients in our clinicalpractice have reported as being negatively affected by con-stipation. We excluded items related to difficulty with finemotor skills, religious ⁄ spiritual practices and vigorousphysical activity. We also included three items related todifficulty participating in activities that require sitting forprolonged periods or which require bending over, and onemeasuring concentration problems.

MeasuresThe constipation-related disability scale. The prelimin-ary CRDS contained 18 items which related to commondaily life activities. Participants were asked to rate thedegree of difficulty they experience performing each ofthe activities with a four-point scale (0 = no difficulty,1 = some difficulty, 2 = much difficulty, and 3 = unableto do). A fifth response category was included, entitled‘does not apply’ for activities that participants did notparticipate in for reasons other than their bowel prob-lems. Items in this category were not included in thescoring.

Convergent validity. Since disease-related disability hasbeen linked to decreased quality of life,12–14 the physicalhealth subscales and Physical Health Composite from theMedical Outcomes Study Short Form-36 (SF-36) wereselected to establish convergent validity for the CRDS.Lower scores indicate worse quality of life.

Divergent validity. Divergent validity is defined aswhether or not an instrument is uncorrelated with mea-sures of unrelated constructs. The Epworth SleepinessScale (ESS) and the Marlowe-Crowne Social DesirabilityScale (SDS) were used to establish divergent validity withthe CRDS as they were expected to be conceptually unre-lated to constipation-related disability. Although sleepi-ness is common in those with chronic illness,23 we didnot expect sleepiness to correlate with constipation-specific effects on daily life. The SDS also was expectedto be unrelated to disability. Moreover, the SDS has beencommonly used as a measure of divergent validity ininstrument development research.24–27 The ESS is aneight-item validated scale that measures an individual’slevel of daytime sleepiness,28 which is not an associatedsymptom of constipation. The SDS29 is a validated ten-item measure of socially acceptable or desirable responsestyles.

Predictive validity. As disability has been established ina number of chronically ill populations to be significantlyassociated with increased medical utilisation and missedwork, we examined three areas of disability impact: (i)Number of self-reported physician visits in the past yeardue to bowel problems, (ii) any self-reported emergencyroom visits due to bowel problems (i.e. yes ⁄ no) and (iii)any self-reported missed work days due to bowel prob-lems (i.e. yes ⁄ no). We also examined a number of otherconstructs that have been shown to be associated withincreased medical utilisation and missed work in other

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Aliment Pharmacol Ther 2012; 35: 183–192 185


populations, such as constipation severity, depressionseverity, general health, age, gender and education.2, 30–35

To assess constipation severity, the ConstipationSeverity Instrument (CSI)16 was used, which is a 16-itemvalidated self-report measure of constipation frequency,severity and bother of symptoms. The CSI consists ofthree subscales: Obstructive Defecation (a = 0.91), Colo-nic Inertia (a = 0.88) and Pain (a = 0.89) and has beenshown to demonstrate excellent reliability and validity(a = 0.90).16

To assess the severity of depression, the Prime-MDDepression Subscale36 was used, which has demonstratedvalidity and reliability.37 Nine items correspond to thespecific symptoms of DSM-IV Major Depressive Episode,with each item rated as yes ⁄ no.

To measure general health, patients rated their generalhealth status over the last year on a one-item Likert typescale ranging from ‘1 = excellent’ to ‘5 = poor.’

Data analysisDifferences between samples (constipated vs. healthysubjects; clinic vs. community) were examined usingt-tests and chi-squared analyses. To establish the compo-nent scales of the CRDS, a principal component analysiswith oblimin (i.e. non-orthogonal) rotation was con-ducted using PASW Version 17.0 software (Chicago, IL,USA).38 The number of factors was determined by factoreigenvalues greater than 1.0 and a noticeable change inthe slopes generated by the scree plot. A confirmatoryfactor analysis was performed on the putative two-factorexploratory model using AMOS 16.0 software (Chicago,IL, USA).38 Maximum likelihood estimation was used toestimate the parameters of the confirmatory factor analy-sis model. Model fit was determined by commonly usedfit indices, including the comparative fit index (CFI), theroot-mean-square error of approximation (RMSEA) andthe Tucker-Lewis incremental fit Index (TLI).39

To assess CRDS reliability, Cronbach’s alphas werecalculated and intraclass correlation coefficients evaluatedtest–retest reliability. Discriminant validity was assessedby comparing the CRDS total and subscale scores of thehealthy controls to the constipated patients. Convergentvalidity was assessed by calculating Pearson correlationcoefficients between the CRDS total score and subscalesand the IBS-QOL. In addition, to assess divergent valid-ity, Pearson correlation coefficients were calculatedbetween the CRDS and the Epworth Sleepiness Scale andthe Marlowe-Crowne Social Desirability Scale.

To assess predictive validity of the CRDS on numberof physician visits in the last year, we used quantile

regression analysis, a nonparametric analytical technique,as the data for number of physician visits in the pastyear were highly skewed. When continuous data are notnormally distributed, quantile regression allows for theestimation of quantile-specific effects that describe theconditional impact of the covariates at the centre (50thpercentile) and at the tails of the distribution (25th and75th percentile).40 This procedure generates a ‘pseudo-R2’, which describes the amount of variance accountedfor in the outcome variance by the predictors at eachquantile. The odds of any ER visits or missed work days(both dichotomous outcomes) in the past year wereexamined with logistic regression analyses. Both thequantile and logistic regression models included termsfor age, gender, educational level, overall rating of gen-eral health, constipation symptom severity (measuredwith the three CSI subscales of Colonic Inertia, Obstruc-tive Defecation, and Pain), depression severity and theCRDS total score. In each regression model, all variableswere entered in one block.

RESULTS

Participant demographicsInformed consent was obtained from 298 participantswith constipation, 240 of whom returned completedquestionnaires (overall response rate 81%). The responserate was 75% from the clinic sample and 91% from thecommunity sample. In addition, a total of 103 healthyvolunteers consented to participate and 100% returnedcompleted questionnaires.

Table 1 shows demographics for the constipated sub-jects compared to healthy controls.

Constipated patients were significantly more likely tobe women (P < 0.001), Caucasian (P < 0.05), and toreport worse general health status (P < 0.001). No differ-ences between the constipated patients and the healthycontrols were observed with respect to age and employ-ment status.

Within the constipated patients, differences existedbetween the clinical sample and the community samplewith regard to age, education and ethnicity. Specifically,the community participants tended to be younger(M = 41.10, s.d. = 10.96 vs. M = 48.73, s.d. = 15.37,P < 0.001), whereas the clinic participants were morelikely to be Caucasian (76.1% vs. 58.2%, P < 0.02). Edu-cation differed by recruitment source with the clinicsample achieving a higher level of education than thecommunity sample, v2 (3, N = 240) = 10.23, P = 0.02.No differences between the clinic and community sample




were observed with respect to gender, general health andemployment status.

Factor analysisResults from the principal component analysis indicateda two-factor solution, accounting for 58.33% of the vari-ance. All factor loadings exceeded 0.40 and did not dem-onstrate cross-loadings of greater than 0.40. Factor 1contained nine items consistent with Work ⁄ LeisureActivities and accounted for 51.38% of the variance. Fac-tor 2 also contained nine items consistent with ADLsand accounted for 6.95% of the variance. Table 2 dis-plays the factor loadings for each item.

Next, a confirmatory factor analysis was conductedfor these two factors. Initially, the adequacy-of-fit statis-tics for the exploratory model was poor. Specifically, thecomparitive fit index (CFI) (obtained value = 0.88) andthe Tucker-Lewis incremental fit index (TLI) (obtainedvalue = 0.86) were both below the acceptable fit criteriaof 0.95.39 Furthermore, the root-mean-square error ofapproximation (RMSEA) (obtained value = 0.10)exceeded the reasonable fit criteria of 0.08.41 Modifica-tion indices suggested an alternative model in which twoitems were deleted from work ⁄ leisure activities factorand three items were deleted from the ADL factor. Mod-ification indices also suggested correlated errors among

Table 1 | Participant demographics and differences withhealthy controls

Constipatedpatients

Healthycontrols Significance

N 240 103

Age (M, s.d.) 45.68(14.78)

43.36(16.95)

NS

Per cent femalegender

82.5 63.0 P < 0.001

Per cent Caucasian 68.8 57.3 P < 0.05

Education (%)

8th grade 0 1 P < 0.01

High school 11.7 2.1

Some college 25.8 17.7

College graduate 33.3 36.5

Graduate school 29.2 42.7

Per cent employed* 58.8 68.0 NS

General health(M, s.d.)

2.71(1.00)

1.75(0.87)

P < 0.001

NS, not significant.

* Employment was defined as working part-time or full-time.

Table 2 | Summary of principal component analysis forthe CRDS (N = 184)

Item

Factor loadings

Leisure ⁄workactivities

Activitiesof dailyliving

Difficulty travelling 0.89 )0.13

Difficulty going to social events,parties, or celebrations

0.88 )0.01

Difficulty participating in leisureactivities, such as going tomovies, club meetings, orrestaurants

0.83 0.07

Difficulty having people to yourhome

0.83 0.03

Difficulty visiting friends or familymembers in their homes

0.79 0.07

Difficulty doing activities thatrequire you to sit for longperiods of time (i.e. car rides,meetings, sitting at a computer)

0.69 0.09

Difficulty having intimate relationswith your spouse or partner

0.57 )0.02

Difficulty participating inrecreational activities, such asbicycling, swimming, walking,or taking part in sports

0.52 0.39

Difficulty working at a job orgoing to school

0.40 0.34

Difficulty cooking )0.07 0.80

Difficulty taking care of yourself(e.g. activities such as bathing orgetting dressed)

)0.17 0.74

Difficulty doing things with or foryour children or grandchildren

0.13 0.67

Difficulty shopping or doing errands 0.20 0.65

Difficulty sleeping 0.05 0.65

Difficulty doing activities whichrequire you to bend over, likegardening, cleaning, or athletics

0.22 0.59

Difficulty taking care of familymembers or people closest toyou

0.36 0.52

Difficulty concentrating ⁄maintainingfocus on tasks

0.29 0.48

Difficulty walking 0.39 0.44

Eigenvalues 9.25 1.25

% of variance 51.38 6.95

Bold font indicates items retained in the confirmatory factoranalysis.




the items ‘difficulty doing activities that require you tosit for long periods of time’ and ‘difficulty participatingin leisure activities’ in the Work ⁄ leisure activities factoras well as ‘difficulty doing activities which require you tobend over’ in the ADL factor. In addition, correlatederrors among the items, ‘difficulty participating in recrea-tional activities’ and ‘difficulty doing activities whichrequire you to bend over’ were suggested. Following thecompletion of the suggested modifications, the revisedconfirmatory factor model provided an improved fit tothe data with acceptable goodness-of-fit indices:CFI = 0.97, TLI = 0.96 and RMSEA = 0.07. In addition,the regression coefficients were all statistically significantand in the predicted direction.

The final CRDS included two factors: Work ⁄ leisureactivities (seven items) and activities of daily living (sixitems). Table 2 displays the items retained following theconfirmatory factor analysis. The subscale scores rangefrom 0 to 21 for the Work ⁄ leisure activities subscale andfrom 0 to 18 for the ADL subscale. The CRDS totalscore ranges from 0 to 39. Higher scores representincreased difficulty completing activities in the respectivedomain due to constipation-related symptoms.

ReliabilityCronbach’s coefficient alphas for the CRDS total score,the Work ⁄ leisure activities subscale, and the ADL sub-scale were excellent at 0.94, 0.92 and 0.87, respectively.Test–retest reliability was very good for the CRDS, withintraclass correlation coefficients for the CRDS totalscore, the Work ⁄ leisure activities subscale, and the ADLsubscale at 0.88, 0.87 and 0.85, respectively.

Discrminant validityAs expected, the CRDS total score was higher for theconstipated sample (M = 9.13, s.d. = 7.83) than that forthe healthy controls (M = 1.96, s.d. = 4.26), t(377) =

)8.74, P < 0.001. Similarly, the Work ⁄ leisure activitiessubscale score was higher for the constipated sample(M = 5.47, s.d. = 4.79) than that for the healthy controls(M = 1.23, s.d. = 2.60), t(381) = )8.50, P < 0.001.Finally, the ADL subscale score was higher for the con-stipated sample (M = 3.73, s.d. = 3.40) than that for thehealthy controls (M = 0.73, s.d. = 1.72), t(388) = )8.50,P < 0.001.

Convergent validity and divergent validityAs shown in Table 3, the CRDS total score, the Work ⁄ Lei-sure Activities subscale, and the ADL subscale all showedmedium to large ()0.31 to )0.53) negative correlations42

(P < 0.001) with the SF-36 physical health scores, indicat-ing that higher levels of disability were correlated withlower ratings of quality of life. These data suggest goodconvergent validity of the CRDS. Table 3 also shows theCRDS total score, Work ⁄ Leisure Activities subscale andADL subscale showed very small42 nonsignificant correla-tions ()0.04 to 0.10) with the Epworth Sleepiness Scaleand the Marlowe-Crowne Social Desirability Scale(P > 0.05), indicative of good divergent validity.

Predictive validityNumber of physician visits in prior year. As shown inTable 4, the following predictors of physician visits wereexamined: Age, gender, general health, education, consti-pation symptom severity, depression severity and thetotal score of the CRDS. Physician visits at the 25th per-centile were significantly related to worse general health(P < 0.001), older age (P = 0.02) and more severeobstructive defecation symptoms (P < 0.001). The 25thpercentile pseudo-R2 was 0.155. At the 50th percentile,physician visits were significantly related to worse gen-eral health (P < .002) and more severe obstructive defe-cation (P < 0.002), with a pseudo R2 at 0.130. However,the 75th percentile of physician visits was significantly

Table 3 | Pearson correlation coefficients indicating convergent and divergent validity

Convergent Validity Divergent Validity

CRDSsubscale

Physicalhealth

Rolephysical

Bodilypain

Generalhealth

Physicalhealthcomposite

EpworthSleepinessScale

SocialDesirabilityScore

Work ⁄ leisure )0.43* )0.46* )0.50* )0.31* )0.47* 0.10 0.01

ADLs )0.53* )0.48* )0.51* )0.32* )0.52* 0.09 0.02

CRDS Total )0.50* )0.49* )0.53* )0.33* )0.51* 0.09 )0.04

ADLs, activities of daily life; CRDS, Constipation-Related Disability Scale.

* P < 0.001.




related to greater constipation-related disability (P =0.008) and worse pain due to constipation (P = 0.016),in addition to worse general health (P = 0.038) andgreater obstructive defecation symptoms (P = 0.002). The75th percentile pseudo-R2 was 0.168.

Missed work in the prior year. Logistic regression analy-sis evaluated the significance of each of the nine variables

described above in predicting whether or not any days ofwork had been missed in the prior year (rated yes vs.no). A test of the full model explained 25.4% of the devi-ance in missing work (v2 = 34.977, d.f. = 9, P < 0.001).As shown in Table 5, only a higher CRDS score wasassociated with missing work (OR = 1.11, 95%CI = 1.06–1.19, P < 0.001).

ER visits in the prior year. Using the same set of covari-ates, the full model was statistically significant andexplained 24.0% of the deviance in making an ER visitin the last year (v2 = 25.7, d.f. = 9, P = 0.002). Table 5shows that younger age (OR = 0.96, 95% CI = 0.92–0.99,P < 0.05), less severe pain (OR = 0.77, 95% CI = 0.65–0.90, P < 0.001) and a higher CRDS score (OR = 1.08,95% CI = 1.00–1.16, P < 0.05) each were significantlyassociated with a visit to the ER in the last year.

DISCUSSIONPrior to the development of the Constipation-RelatedDisability Scale (CRDS), no disease-specific measureexisted that assessed the impact of constipation symp-toms on day-to-day activities. Our data show that theCRDS is a short, easy to administer, self-report measurewith excellent scale and test–retest reliabilities, as well asgood discriminant, convergent, divergent, and predictivevalidity. Results from the confirmatory factor analysisindicated that the CRDS contained two factors whichreflected difficulties with Work ⁄ leisure activities andactivities of daily living (ADL) as a consequence of

Table 4 | Quantile regression estimates for predictors of frequency of doctor’s visits in the past year

Quantile regression in frequency of doctor’s visits in last year

25th 50th 75th

B (SE) 95% CI B (SE) 95% CI B (SE) 95% CI

General health 1.61 (0.41)*** (0.80–2.41) 1.87 (0.59)** (0.71–3.03) 3.17 (1.52)* (0.18–6.16)

Age 0.03 (0.01)* (0.01–0.05) 0.02 (0.02) ()0.02–0.05) 0.01 (0.03) ()0.05–0.05)

Gender )0.11 (0.33) ()0.76–0.53) )0.04 (0.65) ()1.32–1.24) )0.58 (1.68) ()3.89–2.73)

Education 0.86 (0.27)** (0.33–1.39) 0.22 (0.43) ()0.63–1.08) 0.42 (0.66) ()0.87–1.72)

Colonic inertia 0.02 (0.02) ()0.03–0.07) )0.05 (0.05) ()0.14–0.04) )0.05 (0.05) ()0.15–0.06)

Obstructivedefecation

0.16 (0.04)*** (0.08–0.25) 0.17 (0.06)** (0.06–0.28) 0.21 (0.07)** (0.08–0.34)

Pain )0.04 (0.04) ()0.11–0.04) )0.05 (0.05) ()0.15–0.05) )0.17 (0.07)* ())0.31–))0.32)

Depression )0.03 (0.03) ()0.08–0.03) )0.01 (0.04) ()0.09–0.06) 0.01 (0.05) ()0.09–0.01)

CRDS Total 0.01 (0.03) ()0.05–0.06) 0.06 (0.04) ()0.01–0.13) 0.13 (0.05)** (0.04–0.23)

* P < 0.05, ** P < 0.01, *** P < 0.001.

Table 5 | Results of logistic regression analyses examin-ing predictors of emergency room (ER) visits and workabsenteeism

ER visits Work absenteeism

Oddsratio 95% CI

Oddsratio 95% CI

General health 0.57 (0.18–1.77) 0.78 (0.31–2.00)

Age 0.96* (0.92–0.99) 0.97 (0.95–1.00)

Gender 0.76 (0.18–1.77) 0.78 (0.42–2.87)

Education 1.73 (0.67–4.49) 0.55 (0.26–1.19)

Colonic inertia 1.03 (0.94–1.12) 1.00 (0.94–1.07)

Obstructivedefecation

1.09 (0.96–1.23) 1.02 (0.93–1.11)

Pain 0.77** (0.65–0.90) 0.91 (0.82–1.00)

Depression 1.02 (0.94–1.10) 1.04 (0.98–1.11)

CRDS Total 1.08* (1.00–1.16) 1.11** (1.06–1.19)

CRDS, Constipation-Related Disability Scale.

* P < 0.05, ** P < 0.001.




constipation symptoms. These two factors encompass asatisfactory range of activities, including both mandatoryand discretionary life activities and, as such, reflect acomprehensive disease-specific disability measure. In theAppendix, the final version and items for the CRDS areshown.

The need for such a scale is clearly evident whenexamining the impact that chronic constipation has onone’s daily life. The CRDS fills a significant void andmay serve as a necessary tool for assessing the needs of apopulation that has previously been neglected. Aboveand beyond the debilitating consequences it imposes onone’s day-to-day life, the economic burden of chronicconstipation is also evident.11, 43 This is consistent withsimilar studies of chronically ill populations that haveshown that disability is predictive of medical service util-isation and work absenteeism.35

Although there are undoubtedly many reasons whypeople miss work, this model accounted for a 25% of thevariance in both visits to the ER and work absenteeism.In fact, of the variables examined, constipation-relateddisability was the only construct significantly associatedwith missing work in the last year. Moreover, the CRDSwas significantly associated with physician visits at the75th percentile, and accounted for approximately 17% ofthe variance, along with greater constipation symptomseverity and worse general health. Taken together, thispattern of findings suggests that the CRDS adds informa-tion above and beyond that of general health or constipa-tion symptom severity. However, it is important to notethat there are many other factors that might also accountfor further variance in medical utilisation or missed work.For example, among those suffering from a chronic dis-ease, the presence of pain, fatigue, problems with motorcontrol or with cognitive functioning have been shown tosignificantly contribute to missed work and sickleave.35, 44 Although future research should examine theseother factors alongside constipation-related disability, thesuccess of this scale’s predictive validity is important asits utilisation may help guide early intervention andreduce disability. Doing so may benefit the lives of theindividuals plagued by chronic constipation and alsoaddress the issue of resource utilisation, thereby profitingnot only health care providers, but society as a whole.

The current study has notable limitations that mustbe addressed. Demographic differences were observedbetween the constipated patients who were recruitedfrom the clinic compared to the community. Webelieved that sampling patients both who were and werenot seeking treatment would reflect a broader represen-

tation of the general population of constipated individu-als. However, it is not clear what specific impact thegroup differences may have had and, therefore, contin-ued validation across constipated populations is war-ranted.

In addition, it is important to note that our approachto developing the CRDS has some limitations. Althoughwe conducted focus groups with constipated patients andhealth care providers to generate items for our compan-ion measures, the CSI and CRQOL, this approach wasnot utilised for the CRDS. Moreover, we acknowledgethat the VLA was developed for use with rheumatoidarthritis patients; asking constipated patients about theways their day-to-day activities have been limited by con-stipation may have provided a different list of life activi-ties included on the CRDS. Future validation studiesshould consider consulting constipated patients directlyabout the content and could also incorporate an open-ended query to the measure. In addition, the data providesupport for reasonable predictive validity of the CRDS,but given the cross-sectional design of this study, we can-not ascertain that constipation-related disability leads toincreased medical utilisation or work absenteeism. Longi-tudinal data are needed to bear out the directionality ofthis relationship. Finally, although we qualified whetherself-reported medical utilisation or work absenteeism was‘due to bowel problems,’ we did not ask participants toreport whether constipation specifically (or another medi-cal condition that might cause constipation) was the rea-son for their medical visits or missed work; futureresearch will need to help clarify the specific role of con-stipation-related disability on these outcomes. Despitethese limitations, this study provided a comprehensiveevaluation of the reliability and validity of the CRDS.

In conclusion, constipation is a highly prevalent prob-lem, characterised by a number of symptoms that canhave a dramatic impact on an individual’s ability tocomplete day-to-day activities. Although research hasdemonstrated that having a decreased ability to performADLs is related to decreased QOL and increased psycho-logical distress, until now, there has not been a measureof constipation-specific disability. In response to thisvoid, we developed the CRDS. The CRDS demonstratedexcellent reliability, excellent divergent, discriminant andconvergent validity and predictive validity. The develop-ment of the CRDS allows for a standardised measure ofdisease-specific disability that assesses both the magni-tude of disability as well as the specific areas affected.Used in combination with constipation-specific measuresassessing constipation severity and quality of life, the




CRDS will allow for a more comprehensive conceptuali-sation of this condition and the consequences of it.

ACKNOWLEDGEMENTDeclaration of personal and funding interests: None.

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APPENDIX

The Constipation-Related Disability ScaleThese questions are about how your bowel problems affect your ability to do things that are important to you.

Please indicate how much PHYSICAL difficulty you have had over the past week with each of these activities becauseof your bowel problems.

If you do not perform an activity for reasons other than your bowel problems, you should mark ‘Does not apply.’Because of your bowel problems, how much PHYSICAL difficulty have you had with each of the following

activities during the past week?

Activity Nodifficulty0

Somedifficulty1

Muchdifficulty2

Unableto do3

Doesnot apply

1. Doing activities that require you to sit for long periodsof time (i.e. car rides, meetings, sitting at a computer)

2. Doing activities which require you to bend over, likegardening, cleaning, athletics

3. Shopping or doing errands

4. Taking care of family members or people closest to you

5. Doing things with or for your children or grandchildren

6. Going to social events, parties, or celebrations

7. Having people to your home

8. Visiting friends or family members in their homes

9. Walking

10. Concentrating ⁄maintaining focus on tasks

11. Travelling out of town

12. Participating in recreational activities, such as bicycling,swimming, walking, or taking part in sports

13. Participating in leisure activities, such as going tomovies, club meetings, or restaurants




Documents

Development and assessment of the constipation-related disability scale