Journal of Abnormal Child Psychology, Vol. 27, No. 1, 1999, pp. 17-24

Comparing the Strengths and Difficulties Questionnaireand the Child Behavior Checklist: Is Small Beautiful?

Robert Goodman1,2 and Stephen Scott1

Received November 18, 1997; revision received May 12, 1998; accepted September 3, 1998

The Strengths and Difficulties Questionnaire (SDQ) is a brief behavioral screening ques-tionnaire that can be completed in 5 minutes by the parents or teachers of children aged 4to 16; there is a self-report version for 11- to 16-year-olds. In this study, mothers completedthe SDQ and the Child Behavior Checklist (CBCL) on 132 children aged 4 through 7 anddrawn from psychiatric and dental clinics. Scores from the SDQ and CBCL were highlycorrelated and equally able to discriminate psychiatric from dental cases. As judged againsta semistructured interview, the SDQ was significantly better than the CBCL at detectinginattention and hyperactivity, and at least as good at detecting internalizing and externalizingproblems. Mothers of low-risk children were twice as likely to prefer the SDQ.

KEY WORDS: Child psychopathology; prosocial behavior; questionnaires; validity; acceptability.

INTRODUCTION

The Strengths and Difficulties Questionnaire(SDQ) is a brief behavioral screening questionnairethat asks about 25 attributes, some positive and oth-ers negative (Goodman, 1997). The 25 items are di-vided between five scales of five items each,generating scores for Conduct Problems, Inattention-Hyperactivity, Emotional Symptoms, Peer Problems,and Prosocial Behavior; all scales but the last aresummed to generate a Total Difficulties score. Thesame questionnaire can be completed by the parentsor teachers of 4- to 16-year-olds (Goodman, 1997)and there is a parallel self-report version for com-pletion by 11- to 16-year-olds (Goodman, Meltzer, &Bailey, 1998). Extended versions of the SDQ includean impact supplement that asks if the respondent

This article was received and initially reviewed under the editor-ship of Donald K. Routh.

1Department of Child and Adolescent Psychiatry, Institute of Psy-chiatry, London, United Kingdom.

2Address all correspondence, including requests for sample ques-tionnaires, to Robert Goodman, Ph.D., Department of Child andAdolescent Psychiatry, Institute of Psychiatry, De Crespigny Park,London SE5 8AF, United Kingdom.

thinks that the young person has a problem, and ifso, enquires further about chronicity, distress, socialimpairment, and burden for others (Goodman, inpress).

The SDQ is available in over 30 languages andis being widely used in epidemiological, developmen-tal, and clinical research, as well as in routine clinicaland educational practice. Since the same is true ofthe longer established Child Behavior Checklist(CBCL; Achenbach, 1991a), it is clearly important tocompare the properties of the SDQ and CBCL inorder to facilitate communication between re-searchers and practitioners using each measure. In-formation on the relative merits of each could alsoinfluence choice of instrument.

The SDQ and CBCL differ in several respectsthat could alter their psychometric properties. Oneof the most obvious differences is in length—theSDQ has 25 items as compared with the CBCL's118 items on psychopathology alone. Was theSDQ's brevity achieved at the cost of reduced va-lidity?

A second difference between the SDQ andCBCL is that the SDQ items were selected on the

170091-0627/99/0200-OOnS16.00/0 © 1999 Plenum Publishing Corporation

18 Goodman and Scott

basis of nosological concepts as well as factor analy-ses. The relevant concepts are those that underpinthe Diagnostic and Statistical Manual of Mental Dis-orders (4th ed.) (DSM-IV; American Psychiatric As-sociat ion, 1994) and ICD-10 (World Heal thOrganization, 1993) classifications of childhood psy-chopathology. For example, the five items on theSDQ's Inattention-Hyperactivity scale were deliber-ately selected to tap inattention (two items), hyper-activity (two items), and impulsivity (one item)because these are the key symptom domains for aDSM-IV diagnosis of attention-deficit/hyperactivitydisorder (ADHD; APA, 1994) or for an ICD-10 di-agnosis of hyperkinesis (World Health Organization,1993). By contrast, the CBCLs Attention Problemsscale includes several items that have no conceptuallink with the current diagnostic criteria for ADHDor hyperkinesis, e.g., "Nervous, highstrung, or tense."The fact that the SDQ was designed on the basis oftheory as well as previous factor analyses does notseem to have undermined its factor structure; factoranalyses on an independent community sample haveconfirmed that each of the five scales corresponds toa distinct factor (Smedje, Broman, Hetta & vonKnorring, in press). Does the SDQ's reliance on di-agnostic concepts as well as factor analyses influenceits validity?

A further difference between the SDQ andCBCL is that, whereas the CBCL's psychopathologyscales are based entirely on parental endorsementsof negative items (e.g., "Can't concentrate, can't payattention for long"), some of the comparable itemscontributing to the SDQ's psychopathology scales arephrased positively (e.g. "Sees tasks through to theend, good attention span"). The SDQ's greater em-phasis on positive attributes was designed to increasethe questionnaire's acceptability to respondents. Wasthis successful?

Though there have not previously been any di-rect comparisons of the SDQ and the CBCL, indirectevidence suggests that they are probably roughlyequivalent. Scores derived from the CBCL and theRutter parent questionnaire (Rutter, Tizard, & Whit-more, 1970) correlate highly with one another andare of comparable predictive validity (Berg, Lucas,& McGuire, 1992; Fombonne, 1989). Since scoresfrom the SDQ and Rutter questionnaires are alsohighly correlated and of comparable predictive valid-ity (Goodman, 1997), it seems reasonable to inferthat the SDQ and the CBCL are themselves highlycorrelated and of comparable validity. This study was

the first direct test of how the SDQ and CBCL com-pare.

METHOD

Overview

SDQ and CBCL questionnaires were completedby the mothers of 132 children aged 4 through 7years. One part of the sample was from a low-psy-chiatric-risk population, being recruited from a chil-dren's dental clinic. The other part came from ahigh-psychiatric-risk population, being recruited fromthree child psychiatric clinics. The predictive validityof the two questionnaires was examined by estab-lishing how well each questionnaire was able to dis-tinguish between the low- and high-risk samples, asindexed by the area under receiver operating char-acteristic (ROC) curves. Parental preference wasonly established for the dental sample. Detailed in-terviews with parents about their children's psycho-pathology were only carried out for the psychiatricsample.

Low-Risk Sample

The mothers of children attending a children'sdepartment of a London dental hospital were askedto complete the two questionnaires while awaitingtheir clinic appointments if their children were agedfrom 4 years, 0 months, to 7 years, 11 months. Mostof the mothers approached did agree to take part,though the proportion of refusals was not systemati-cally recorded since, as explained subsequently, thestatistical analyses did not require the sample to berepresentative. Completed questionnaires were ob-tained on 71 children.

High-Risk Sample

As part of an ongoing study evaluating the ef-fectiveness of parent management training, parentsfrom three child psychiatric clinics in and aroundLondon were recruited if they had children aged be-tween 3 and 8 years referred with externalizing prob-lems in the absence of severe language problems orknown mental retardation. The high-risk sample forthe present study consists of the first 61 childrenaged from 4 years, 0 months, to 7 years, 11 months,

Comparison of SDQ and CBCL 19

whose parents were enroled in parent traininggroups. Children aged 3 years were excluded fromthe present study since neither the SDQ nor theCBCL questionnaire was designed for children underthe age of 4,

Questionnaires

Mothers were administered the SDQ (Good-man, 1997) and CBCL (Achenbach, 1991a) in ran-dom order on a single occasion. For the psychiatricsample, the questionnaires were obtained prior tothe intervention. Both questionnaires were scoredin the standard manner (Achenbach, 1991a; Good-man, 1997). Sample copies (in a wide range of lan-guages) and scoring instructions are available onrequest.

While the psychometric properties of theCBCL are well known and conveniently summa-rized (Achenbach, 1991a), reports of the psy-chometric properties of the SDQ are dividedbetween several recent papers, warranting a briefsummary. Given the well-established validity andreliability of the Rutter questionnaires (Elander &Rutter, 1996), high correlations between the SDQand Rutter questionnaires provided evidence forthe concurrent validity of the informant-ratedSDQ; receiver operating characteristic analysesalso showed that the Rutter questionnaire andSDQ were of comparable predict ive val idi ty(Goodman, 1997). The internal reliabilities of par-ent-completed SDQ scales were investigated in aSwedish general population sample (N = 900),with Cronbach's alpha being .76 for Total score,.75 for Inattention-Hyperactivity, .70 for ProsocialBehavior, .61 for Emotional Symptoms, .54 forConduct Problems, and .51 for Peer Problems(Smedje et al., in press). Test-retest reliabilitieshave been examined in a British general popula-tion sample; when parents of 34 of these childrencompleted SDQs on two occasions between 3 and4 weeks apart, the intraclass correlations were .85for Total score, .75 for Inattention-Hyperactivity,.81 for Prosocial Behavior, .70 for EmotionalSymptoms, .74 for Conduct Problems, and .83 forPeer Problems (Goodman, in press; Goodman, un-published observations). Smedje et al. (1998) re-ported a test-retest reliability of .96 for total scoreover a 2-week period in their small pilot sample(N = 15).

Questionnaire Preference

Immediately after completing both questionnaires,mothers of the low-risk sample were asked to tick abox indicating which of the two questionnaires theypreferred. To avoid response bias related to the orderin which the questionnaires were listed in the prefer-ence question, the order of listing was randomized.

Parent Interview

Within a week of completing the two question-naires, the mothers of all 61 children in the psychi-a t r ic sample were admin i s t e red a va l ida tedsemistructured interview about their child's emo-tional and behavioral symptoms: the Parental Ac-count of Child Symptoms (PACS; Taylor, Schacher,Thorley, & Wieselberg, 1986). The PACS interviewswere administered by trained interviewers who wereblind to the questionnaire scores. Parents were askedfor detailed descriptions of their children's behaviorover the previous year, with interviewers then ratingthe severity and frequency of these behaviors on thebasis of their training and written criteria. The Inat-tention-Hyperactivity scale was scored in the stand-ard manner by summing the frequency and severityitems for attention span (time spent on a single ac-tivity rated separately for four different kinds of ac-tivity), restlessness (moving about during the sameactivities), fidgetiness (movements of parts of thebody during the same activities), and activity level(rated for structured situations such as mealtimesand car journeys). Similarly, the Externalizing scalewas calculated from items concerning temper tan-trums, lying, stealing, defiance, disobedience,truanting, and destructiveness. The Internalizingscale was calculated from items on misery, worrying,fears, hypochondriasis, and obsessionality. In theoriginal validation study, interrater reliabilities forpairs of raters ranged from .92 to .95 for the Inat-tention-Hyperactivity scale, from .89 to .95 for theExternalizing scale, and from .79 to .90 for the In-ternalizing scale (Taylor et al., 1986). Additional nor-mative data on this interview are presented in Taylor,Sandberg, Thorley, and Giles (1991).

Statistical Analyses

Using analyses of receiver operating charac-teristic curves to compare the discriminant validity of

20 Goodman and Scott

Comparison of SDQ and CBCL 21

the two questionnaires does not depend on the rep-resentativeness of the two samples; it assumes onlythat psychiatric disorder is commoner in the high-riskthan the low-risk group. Since the ROC curves forthe SDQ and CBCL were derived from the same setof patients, the statistical comparison of the areas un-der these ROC curves allowed for the paired natureof the data (Hanley & McNeil, 1983). Comparisonsof correlations also allowed for the paired nature ofthe data, using structural equation modeling (EQS;Bentler, 1989) to examine whether constraining thecorrelations to be the same resulted in a significantlypoorer fit. For example, when an SDQ-interview cor-relation differed from the corresponding CBCL-in-terview correlation, the significance of this differencewas examined by comparing two different structuralequation models: one allowing the correlations to bedifferent and the other constraining the correlationsto be equal. The difference in correlations was sig-nificant if the goodness of fit of the constrainedmodel was significantly poorer than that of the un-constrained model (Dunn, Everitt, & Pickles, 1993).

tion, the area under the curve would be 1.0 for ameasure that discriminated perfectly, and .5 for ameasure that discriminated with no better thanchance accuracy. Both questionnaires discriminatedwell, with an area under the curve of around .95 forTotal and Externalizing scales. In no instance did thearea under the curve for the equivalent SDQ andCBCL scales differ significantly.

SDQ-CBCL Correlations

Table II shows the correlations between theequivalent SDQ and CBCL scales. All correlationswere statistically significant (p < .001). Though theProsocial scale of the SDQ and the competence scaleof the CBCL share a focus on positive attributes,they were not considered to be equivalent scalessince they differ so markedly in item content.

Correlation with Interview Scores

RESULTS

Age and Gender

The two samples did not differ significantly inage: The mean age (SD) of the psychiatric samplewas 6.0 years (1.1) while that of the dental samplewas 6.2 years (1.2) (t = 0.60, 130 df, n.s.). Thoughthe proportion of males was higher in the psychiatricsample (74%, 45/61) than in the dental sample (56%,40/71), the difference was not significant (continuity-adjusted i2 = 3.62, 1 df, p = .06). The results re-ported here are for boys and girls combined, but asimilar pattern of results emerged when boys andgirls were analyzed separately.

Discriminating Between Low-Risk and High-RiskSamples

Using both questionnaires, there were substan-tial mean differences in the scores obtained by thelow-risk and high-risk samples (Table I). The relativeability of the SDQ and CBCL to distinguish betweenthese two samples can be judged from the areas un-der the receiver operating characteristic curves forequivalent scales (Table I). As a guide to interpreta-

For children in the psychiatric sample, it waspossible to examine how well the questionnairescores predicted detailed investigator-based ratingsof internalizing symptoms, inattention-hyperactivity,and externalizing problems, derived from semistruc-tured parent interviews. Table III shows the correla-tions between these interview measures and theequivalent SDQ and CBCL scores, e.g., between theinterview measure of internalizing symptoms andeither the SDQ Emotional score or the CBCL Inter-nalizing score. For internalizing symptoms and exter-nalizing problems, the interview-questionnairecorrelations were comparable for the two question-naires. For inattention-hyperactivity, however, the in-terview rating correlated significantly more highlywith the SDQ score than with the CBCL score; con-straining the two correlations to be equal led to asignificant worsening of the structural equationmodel (x2 = 6.14, 1 df, p < .02). When consideringthe magnitude of some of the correlations, it is worthremembering that, in a clinical sample, symptomscores are bunched toward the upper end of therange, resulting in lower correlations than would befound in a more heterogenous sample. However, thiseffect will have applied equally to interview-SDQ andinterview-CBCL correlations.

22 Goodman and Scott

Cross-Domain Correlations for Each Questionnaire

The three main domains of psychopathologytapped by each questionnaire are externalizing prob-lems, inattention-hyperactivity, and internalizingsymptoms. Table IV shows how scores for these threedomains correlated with one another, consideringeach questionnaire separately. The externalizing-in-attention correlations were comparable whether ob-tained from the SDQ or CBCL; a structural equationmodel that constrained the two to be equal did notfit significantly worse than an unconstrained model(X2 = 2.52, 1 df, p = .11). By contrast, the external-izing-internalizing and inattention-internalizing cor-relations were significantly higher with the CBCLthan with the SDQ (f = 18.43, 1 df, p < .001 forexternalizing-internalizing; x2 = 18.54, 1 df, p < .001for inattention-internalizing).

For the children in the psychiatric sample, it waspossible to compare cross-domain correlations forthe questionnaire and interview measures. The exter-nalizing-internalizing correlation was .05 for the in-terview, .02 for the SDQ, and .52 for the CBCL(CBCL correlation but not SDQ correlation signifi-cantly different from the interview correlation; %2 =10.51, 1 df, p < .002). The inattention-internalizingcorrelation was .13 for the interview, .05 for the

SDQ, and .42 for the CBCL (representing a trendfor the CBCL correlation but not the SDQ correla-tion to differ from the interview correlation; j} =2.75, 1 df,p < .1).

Questionnaire Preference

Of the 71 mothers from the low-risk sample, 64expressed a preference for one or other question-naire: 41 preferred the SDQ and 23 preferred theCBCL—a significant difference (sign test, z = 2.25,p < .025). Mothers from the high-risk sample werenot asked which questionnaire they preferred.

DISCUSSION

As hypothesized, scores derived from the in-formant-rated Strengths and Difficulties Question-naire (Goodman, 1997) and the Child BehaviorChecklist (Achenbach, 1991a) correlated highly withone another, and the two questionnaires were equallyable to discriminate between children drawn fromhigh-risk and low-risk samples. This equivalence isstriking since the SDQ is only around a fifth of thelength of the CBCL.

Other things being equal, shorter scales are nor-mally less reliable than longer scales, thereby attenu-ating validity too (Streiner & Norman, 1989). In thisinstance, though, the brevity of the SDQ did not reduceits criterion validity, as judged against a standardizedsemistructured interview: The interview-based ratingscorrelated more highly with the SDQ than with theCBCL scores, with this difference being statisticallysignificant for inattention-hyperactivity. Why shouldthe 5-item SDQ Inattention-Hyperactivity scale have

Table II. Correlations of Equivalent SDQ and CBCL Scales"

Problem scales

TotalExternalizing/ConductInattention/HyperactivityInternalizing/EmotionalSocial/Peer

SDQ-CBCL correlations

.87

.84

.71

.74

.59

"SDQ = Strength and Difficulties Questionnaire; CBCL = ChildBehavior Checklist. All correlations significant at p < .001.

Table IV. Intercorrelations of Different Scales from theSame Questionnairea

Correlations of the two scores

Problem scales

Externalizing-InattentionExternalizing-internalizingInattention-Internalizing

For SDQ

.65

.37"

.35"

For CBCL

.72

.63

.63

aSDQ = Strengths and Difficulties Questionnaire; CBCL =Child Behavior Checklist.

bSignificantly lower for SDQ than CBCL, p < .001.

Table III. Correlations of Questionnaires and Interview Scalesa

Correlations between interviewmeasure and:

Problem scales

Externalizing/ConductInattention/HyperactivityInternalizing/Emotional

SDQ

.64

.43"

.53

CBCL

.52

.15

.44

aSDQ = Strengths and Difficulties Questionnaire; CBCL = ChildBehavior Checklist.

bSignificantly greater SDQ-interview correlation than CBCL-inter-view correlation, p < .02.

Comparison of SDQ and CBCL 23

greater criterion validity than the corresponding 11-item CBCL scale? One possible explanation is thatthe SDQ scale has greater content validity since itemselection was guided by DSM-IV and ICD-10 diag-nostic criteria for ADHD (APA, 1994) and hyperki-nesis (World Health Organization, 1993). Drawing ona large body of empirical studies, both classificationsemphasize that the core symptoms domains are in-attention, hyperactivity, and impulsiveness. All fiveSDQ items are drawn from these three domains,whereas many of the CBCL items tap different symp-tom domains: immaturity, confusion, nervousness,twitching, poor school work, and clumsiness. Increas-ing scale length by including items that are concep-tually marginal may only serve to undermine validity.

The correlation between the Internalizing andExternalizing scales was significantly lower for theSDQ than for the CBCL. This was not because allinterscale correlations were attenuated for theshorter questionnaire: The externalizing-inattentioncorrelation was almost equally high for the SDQ andCBCL. Two alternative explanations are plausible.On the one hand, the lower SDQ internalizing-ex-ternalizing correlation may reflect the SDQ scalesbeing less contaminated by one another than thecomparable scales from the CBCL. Alternatively, thehigher CBCL internalizing-externalizing correlationmay be a more accurate reflection of real comorbid-ity. While there is no doubt that comorbidity exists(Caron & Rutter, 1991), the question is whether thiscomorbidity is underestimated by the SDQ or over-estimated by the CBCL. The present findings aremore suggestive of the latter since, when interview-based correlations were low, SDQ correlations werealso low, whereas CBCL correlations remained high.These findings require confirmation on larger andmore representative samples, but they do support thenotion that the CBCLs Internalizing and Externaliz-ing scales are indeed more contaminated by one an-other than are the comparable SDQ scales.

Parents of the low-risk sample were significantlymore likely to prefer the SDQ to the CBCL, perhapsbecause of the SDQ's brevity and greater emphasison strengths. The preference of parents whose chil-dren are at high psychiatric risk has yet to be estab-lished; perhaps they welcome the opportunityprovided by the CBCL to report on a broader rangeof psychopathology.

The results of this study are necessarily prelimi-nary, being based on a comparison of two relativelysmall samples of young children at high and low risk

of psychiatric disorders. It will obviously be impor-tant to attempt to replicate these findings on abroader age range, using larger samples, includingcommunity samples and diverse clinical samples.Such studies could also compare the informant-ratedSDQ completed by teachers with the Teacher ReportForm (TRF; Achenbach, 1991b), and the self-reportSDQ (Goodman et al., 1998) with the Youth Self-Report (YSR; Achenbach, 1991c).

Pending such larger-scale studies, the currentfindings suggest that the SDQ and CBCL are com-parable in many ways. Consequently, either question-naire would be suitable for many purposes. In somerespects, however, the two questionnaires have differ-ent strengths. The SDQ's brevity and its acceptabilityto the parents of low-risk children may make it a par-ticularly suitable screening measure for communitystudies where response rates are liable to be under-mined by long or negatively slanted questionnaires.The SDQ may also provide a more useful measureof inattention and hyperactivity. On the other hand,the CBCL covers a broader range of problems, par-ticularly suiting it for studies or clinical assessmentsthat require coverage of rare as well as commonforms of childhood psychopathology. Both question-naires have their value but serve somewhat differentpurposes.

ACKNOWLEDGMENTS

We are very grateful to all participating parents;to Hilary Richards, Quentin Spender, Pippa Hoad,Julia Featherstone, Jenny Price, Rosemarie Berry,Moira Doolan, and Deborah Fulford for their assis-tance in data collection and coding; and to all thestaff of the clinics that took part in the study: theDepartment of Paediatric Dentistry of King's DentalInstitute; the Children's Department of the MaudsleyHospital; the Child and Family Psychiatry Clinic,Croydon; and the Child and Family Service for Men-tal Health, Chichester. Data on the psychiatric sam-ple were obtained in the course of a study fundedby the National Health Service Research and Devel-opment Executive.

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