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Two Times Four Is Four: OCD Dimensions,Classes, and Categories

MARCO A. GRADOS, M.D., M.P.H., AND MARK A. RIDDLE, M.D.

Recent research on the phenomenology, etiology, andpathophysiology of pediatric obsessive-compulsive disorder(OCD) signals a renewed interest in pediatric neuro-psychiatric disorders. Pediatric OCD is one of the fewdisorders that mimic the adult form of the disorder inits breadth and depth; that is, it appears in a full-blownform even in prepubertal ages. This is not the case for

schizophrenia, bipolar disorder, or major depression.Following the paradigm of early-onset diabetes and otherpathophysiologically better understood diseases, pediatricOCD is plausibly more biologically driven or more geneticthan its adult-onset form. This greater biological relevanceis demonstrated by family studies that find higher ratesof familial OCD when child OCD probands are used.1

In this vein, one of the most active research domains inOCD, is the search for biologically meaningful subpheno-types that would facilitate etiological research, includinggene discovery.

In this issue of theJournal, Mataix-Cols et al.2 and Stewartet al.3 examine the symptom architecture of pediatric OCD

using data reduction techniques that have been widely used inthe adult OCD literature. Mataix-Cols et al.2 considerwhether symptom dimensions in pediatric OCD arepreserved with respect to symptoms dimensions in adultOCD samples. In the adult OCD literature, four factors arecommonly reported to explain variance using principalcomponents analysis (PCA): contamination/cleaning, aggres-sive/sexual/religious obsessions, ordering/symmetry, andhoarding.4,5 The statistical technique used by Mataix-Colset al. on a sample of 238 children and adolescents takes a

similar approach to those previously reported, namely,semiquantitative data (symptom counts within particularcategories) submitted to PCA with varimax rotation. The fourderived factors are comparable to adult PCA symptomdimension factors, with the exception that hoarding iscomingled with checking symptoms in the child sample.Interestingly, in this child sample, hoarding was correlated

with OCD-related measures of slowness, responsibility,indecisiveness and doubt, and higher depression severityand was more common in girls compared to boys, high-lighting a particularly vulnerable subset of children withOCD.

In turn, Stewart et al.2 report on a confirmatory factoranalysis (CFA) of three age group samples: children,adolescents, and adults with OCD. This ambitious articleis a tour de force in OCD symptom data reduction.Although the limitations of the methods and sampling leavesome questions unanswered, this study does advanceresearch in the field. Using cross-sectional samples, model-fitting methods are applied to measure fit of these data to the

Summerfeldt et al.4 four-factor solution. Summerfeldt et al.4had applied CFA testing of three-, four- and five-factormodels, concluding that the four-factor model best fit OCDcategory symptom, but not item-level, data in adults. Thiscategory symptom analysis assumes that the 60+ symptomslisted in the Yale-Brown Obsessive Compulsive Scale aregrouped correctly into 13 categories. In Stewart et al.,3

categorical data on the three different age samples are used totest the fit of the data to the Summerfeldt et al.4 four-factorsolution. The results show that, in fact, the four-factorsolution continues to best fit OCD categorical symptomdata in each of the three samples across ages using multiple-group CFA.

In summary, the analyses by Mataix-Cols et al.2 andStewart et al.3 of OCD symptom structure in youths yieldfour-factor solutions similar to those in Summerfeldt et al.4

The authors note that although there is similarity in symptomstructure across ages, this is suggestive but not confirmatory ofsymptom stability. Taken together, these results, although

Accepted March 10, 2008.

Drs. Grados and Riddle are with the Department of Psychiatry and BehavioralSciences, Johns Hopkins University School of Medicine.

Correspondence to Dr. Marco A. Grados, 600 N. Wolfe Street, CMSC 346,Baltimore, MD 21287; e-mail: mjgrados@jhmi.edu.

0890-8567/08/4707-0731*2008 by the American Academy of Child and

Adolescent Psychiatry.

DOI: 10.1097/CHI.0b013e318173f720

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consistent, should be tempered with the following observa-tions: PCA is not an ideal method to derive factors fromcategorical or semiquantitative data; factor analyses thatderive categories from the individual items rather thanassuming that the items are categorized accurately by the Yale-Brown Obsessive Compulsive Scale now suggest a five-factormodel as the best solution6; the adult sample in Stewart et al.3

had been used to derive the four-factor solution; there is ahigh factorYfactor correlation between OCD factors in thefour-factor model.

Most important, the variance explained by the four-factormodels published to date are usually in the range of 50% to60%, leaving a large amount of variance unexplained in allof the published solutions. Thus, the debate continues aboutwhether factor dimensions in OCD have extensive researchor clinical utility,7 beyond the fact that they can be used tosimplify clinical data. The hoarding dimension is oftenconsidered to identify a unique subgroup of OCD, giventreatment and neuroimaging studies,8,9 but there is only onequestion in the Children`s Yale-Brown Obsessive Compul-

sive Scale or Yale-Brown Obsessive Compulsive Scale thataddresses hoarding, limiting the utility of any factor analysis.Another symptom dimension that is mentioned as heuristicis the contamination/cleaning factor,10 but the identificationof children who are washers or have other contaminationfears and cleaning rituals is generally not problematic. Thatis, this factor does not reduce clinical data substantially.Thus, the immediate clinical utility of factor-analytic datais not readily apparent, but holds promise, given thestatistical attraction of having a quantitative variable foruse in biological research. Furthermore, linkage and/orassociation studies using OCD factors will become morecommon in the near future. For example, Hasler and

colleagues11 recently reported on the association of theserotonin transporter variant SS with high scores onthe ordering/symmetry factor and on the familiality of thehoarding and taboo factors.12

However, compared to factor analysis, methods that exploresymptom or comorbid disorderYlevel data in OCD may bemore germane for clinical and research purposes. Latent classanalysis (LCA), for example, provides a model-fitting techniquethat focuses on person-centered variables. This can beextremely useful in OCD, a disorder that has a large panoplyof disorder-specific symptoms and frequent comorbidities.Using this method, different classes of individuals can beidentified, which, at face value, may have different pathophy-

siological substrates and treatment needs. The co-occurrence ofattention-deficit/hyperactivity disorder, in particular, maydifferentiate groups of children with OCD, distinguishingOCD linked to neurodevelopmental disorders such asattention-deficit/hyperactivity disorder and tic disorders13

from OCD linked to anxiety disorders. In adult samples,

comorbid depressive, anxiety, and grooming disorders maydifferentiate OCD classes. Although few LCAs of OCD havebeen published to date,14 newer studies are expected to fillthis gap.

Finally, latent profile analysis may constitute a hybridmethod that marries exploratory factor analysis/CFA toLCA methods. In this approach, factor scores are used to

classify individuals as hoarders, washers, and so forth, andthen these classified individuals are submitted to LCA. In apreliminary unpublished analysis by our group, threeclasses of individuals emerged from a latent profile analysis:one with high contamination/cleaning and sex/aggressive/religious factor scores, one with high ordering/symmetryand repeating/counting factor scores, and one in which allfour factor scores were high. Thus, this yet-to-be-exploredapproach may yield a classification of OCD that usesinformation from both exploratory factor analysis/CFAand LCA.

Phenomenological subtyping will play an important rolein research designed to elucidate the etiology of OCD, and

the worthy efforts of Mataix-Cols et al.2 and Stewart et al.3in this issue of the Journalare a welcome addition to theliterature. However, the field is stil l under development andfuture research will determine whether symptom dimen-sions, OCD classes, or merely the categorical diagnosis ofOCD best describe and are correlated with etiological,pathophysiological, and treatment-need pathways in pedia-tric OCD.

Disclosure: Dr. Riddle has consulted to Shire and Johnson & Johnson;served as a scientific advisor to Jazz; has received funding fromNIMH and NICHHD; has participated in not-for-profit organiza-tion activities for the University of Florida, the University of

Maryland, and Long Island Jewish Health System; and offered expertopinions to the Gleason Flynn law firm. Dr. Grados reports noconflicts of interest.

REFERENCES

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Adolesc Psychiatry. 2008;47:773Y778.3. Stewart SE, Rosario MC, Baer L, et al. Four-factor structure of obsessive-

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EDITORIAL

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