0005-7967/92 $5.00+0.00 Copyright Q 1992 Pergamon Press Ltd
Behau.Res.Ther.Vol.30,No.6,pp.631437, 1992 Printed in Great Britain. All rights reserved
OBSESSIONS AND COMPULSIONS: DIMENSIONAL STRUCTURE, RELIABILITY, CONVERGENT AND DIVERGENT VALIDITY OF THE PADUA INVENTORY PATRICIA Free University,
Faculty
VAN OPPEN
of Medicine, Department of Psychiatry at the Amsterdam Valeriusplein 9, 1075 BG Amsterdam, The Netherlands (Received 22 November
Psychiatric
Centre,
1991)
Summary-This study presents data on dimensional structure, reliability, convergent and divergent validity of the Padua Inventory (PI). In a sample (n = 430) of normal Dutch subjects. The dimensional structure and the strength of the factors were comparable to those found in the Italian sample. The reliability of the PI was found to be satisfactory. As hypothesized substantial correlations were found between the PI and related scales of the Maudsley Obsessive-Compulsive Inventory (MOCI) and between the PI and the subscales Sensitivity, Hostility and Depression of the revised version of the Symptom Checklist. Low correlations were found between the PI on the one side and the Eysenck Personality Ouestionnaire revised Extraversion. Psvchoticism and Social Desirabilitv scale on the other side. Finallv. the mean score of the PI differs across the Italian, American and Dutch samples. This is of theoretical interest and deserves further study.
INTRODUCTION
of obsesRecent reviews of the psychometric features of rating scales for the assessment siveecompulsive disorder (OCD) and symptoms (Kozak, Foa & McCarthy, 1988; Goodman & Price, 1990; Goodman, Price, Rasmussen, Mazure, Fleischmann, Hill, Henninger & Charney, 1989) point to the shortcomings of the existing rating scales, including lack of specificity for obsessiveecompulsive symptoms, confusion of trait with state measures, examination of only certain types of obsessions and compulsions, and inadequate analysis of or poor scale psychometric properties (e.g. lack of factor constancy, insufficient sensitivity to detect treatment outcome, low convergent validity). There is also a lack of questionnaires which delineate obsessions and covert rituals. Of the existing self-report inventories, the Leyton Obsessional Inventory (LOI; Cooper, 1970), the Maudsley Obsessive-Compulsive Inventory (MOCI; Hodgson & Rachman, 1977) and the Compulsive Activity Checklist (CAC; Philpott, 1975) are the three most widely used self-rating scales. For the MOCI and the CAC only two strong factors were found: contamination (washing) and checking (Chan, 1990; Hodgson & Rachman, 1977; Kraaijkamp, Emmelkamp & van der Hout, 1988; Sternberger dz Burns, 1990a). More recently, a new self-report inventory, termed the Padua Inventory (PI; Sanavio, 1988), has been described to hold promise as a measure which will allow an accurate quantification of OCD symptoms, since it is the only self-report measure which includes strong obsessional dimensions as distinct from compulsive dimensions (Sanavio, 1988; Sternberger & Burns, 1990b). The PI was developed in Italian by Sanavio (1988) to obtain the most important and frequent types of obsessional complaints. The PI contains not only items which measure intrusive thoughts, doubts, checking and cleaning behaviours, but also items pertaining to senseless or unacceptable urges, repetitive thinking about low-probability dangers, recurrent repugnant images etc. This inventory is composed of statements gathered by interviews of obsessional patients and studies with normals as well as neurotic and obsessive-compulsive patients. Factor analysis of data of 967 normal adult Ss resulted in a 4 factor solution: (1) impaired control of mental activities; (2) becoming contaminated; (3) checking behaviours; and (4) urges and worries of losing control over motor behaviours (Sanavio, 1988). Furthermore, in a sample of students, the PI General scale was found to correlate substantially with the MOCI (0.70), and the LO1 (0.71 with Symptom and 0.66 with Trait scales), and less strongly so, at clearly lower magnitudes, with non-homologous measures 631
PATRKJA VAN OPPEN
632
(e.g. Extraversion - 0.10, Psychoticism 0.09). Test-retest reliability of students (during a 30-day interval) and internal consistency of the scale were found to be satisfactory. Sternberger and Burns (1990b) examined the psychometric properties of the PI with an American college population. Exploratory factor analysis suggested a 4 factor solution which was described to be very similar to that found in the original Italian study of the PI. Internal consistencies for the subscales, according to Sanavio (1988), were reported to be good (range of as: 0.77-0.89). The present study was designed to investigate the generalizability of and to extend the findings of Sanavio (198X) and Sternberger and Burns (1990b) by studying the PI in a Dutch context using community volunteers as 5’s. Such an attempt seems useful for two reasons. First, with the availability of a standard, reliable and valid form of the PI in different countries, comparisons of patient data across research and treatment centres both within and across countries can be justifiably carried out. Second a standard form could be utilized for increasing our knowledge on similarities and differences in the cross-national incidence of obsessional symptoms. Specifically, the aims of the present study were 3-fold, namely to (a) investigate the cross-national stability of the dimensional structure underlying the PI (Sanavio, 1988), (b) establish the internal consistency and the test-retest reliability over an S-week interval of the different PI subscales, and (c) assess the convergent and divergent validity of the different PI scales. METHOD Subjects and procedwes
Participants in the present study were recruited by means of a mail survey. An at random taken sample (n = 1000) was acquired by a municipal office of a medium size municipality. Several questionnaires were mailed to the Ss, preceded by an initial covering letter in which the purpose of the two-stage follow-up survey was stated. The time frame between first and second testing was 8 weeks. Ss willing to participate in the follow-up study were asked either to state their names and addresses or to complete the questionnaires anonymously when unwilling to do so. A pre-addressed envelope stamped Return was enclosed to facilitate response. After deduction of the Ss who had moved or deceased the total sample consists of 961 5’s. One reminder letter was sent out at a fortnightly interval yielding a total response of 430 participants (45%). Of these 430 participants 191 Ss participated in the test-retest study. The sample (all Dutch citizens) consisted of 188 males (44%) and 242 females (56%). The sexes were comparable in terms of age: 40.59 yr (SD = 13.05, range: 18-68) and 38.47 yr (SD = 13.06, range: 18-65) respectively. With regard to their marital status 75% of the Ss were either married or cohabiting. Of all Ss 17% reported being unmarried and living without a partner, while 4% were divorced and 3% were widows/widowers. Almost one-tenth (9%) of the Ss followed only elementary school or less. More than one third (37%) did finish the advanced elementary education and one third (33%) completed modern (secondary) school. Another 19% had at least some college education. In terms of sexes, marital status and education this sample is a fairly good representative sample of the Dutch population. Measures
The following measures were completed: (1) The PI (Sanavio, 1988), consisting of 60 items: range O-240. (2) The MOCT (Wodgson & Rachman, 1977), a 30-item true-false self-report inventory. In the present study the total scale, the subscale washing, checking, and slowness were used. For a Dutch sample the ‘slowness’ subscale appeared to be less useful (Kraaijkamp et al., 1988). (3) The revised version of the Symptom Checklist (SCL-90-R; Derogatis, 1977), a multidimensional self-report inventory of current psychiatric symptoms; range 90-450. The Dutch version of the SCL-90-R provides scores on the dimensions: Agoraphobia, Somatization, Hostility, Depression, Sensitivity, Anxiety, Obsessive-Compulsive problems, and Sleep Disturbance (Arrindell & Ettema, 1986).
Obsessions and compulsions
633
(FQ; Marks & Matthews, 1979), consisting of 20 items, rated on (4) The Fear Questionnaire a 9-point continuum. The FQ yields four subscores: Agoraphobic fears, Social fears, Blood-Injury fears, and an Anxiety-Depression dimension. Questionnaire revised (EPQ-R; Eysenck & Eysenck, (5) The short-scale Eysenck Personality 1983) consisting of 48 yes-no questions. This questionnaire measures the personality dimensions of Neuroticism, Psychoticism, and Extraversion; in addition it results in a score for Social Desirability. Statistics The method for determining cross-national stability of the dimensional structure underlying the PI involved the comparison of factors (components) from other samples with those obtained in the original sample on the basis of ‘perfectly-congruent weights’ (Ten Berge, 1986). The purpose of this method is to determine recoverableness of components from an original study in a replication study with the same interpretations and to evaluate the amounts of variance they explain (Ten Berge, 1986). The matrix of components weights obtained in the original study were used to cross-validate these components in the replication study. Recoverableness can be defined in terms of amounts of variance explained. Therefore, the separate amounts of variance explained by each of any hypothetical factor in the replication study are of major interest, The percentage may vary from 0 to 100%. Besides the strength of each factor, Ten Berge’s approach advocates that the inter-correlations among factors be considered in the interpretative process as well. The VARIMAX rotated 4-factor principal solution of normal Ss (n = 967) reported in Sanavio (1988) was used as the theoretical structure. Actual calculations involved were performed by using the Pekon (PErfect CONgruence) computer programme (Camstra, 1985). Cronbach’s c( coefficient served as measure of internal consistency. To assess convergent and divergent validity, correlations among PI subscales and other scales were determined. For the test-retest reliability Spearman correlations were calculated.
RESULTS
The means and standard deviations of the total PI scores are given in Table 1. There was no significant difference between females and males [t (428) = - 1.78, P = 0.08 NS]. But, there was a significant gender difference on two subscales: (1) impaired control of mental activities [t(428) = -3.26, P = O.OOl], and (2) becoming contaminated [t(426.61) = -2.17, P = 0.031. The female and male mean scores in this study differed from the mean scores in the Italian as well as in the American sample. Dimensional
structure
Pekon determines the strength of the loadings on the original factors in the new material. All items loaded on the respective factors (at least 0.49). Except for item 57 (“I feel I have to make special gestures or walk in a certain way”) which loaded nearly equal on factor (1) (0.37) and factor (4) (0.39), and for item 60 (“I invent useless worries about germs and diseases”) which loaded equal on factor (1) (0.46) and factor (2) (0.46).
Table I. PI scores: means and standard deviations of the Italian, American and Dutch samples
Dutch sample Males Females American sample Males Females Italian sample Males Females
n
Mean
SD
188 242
25.8 29.4
20.8 20.7
294 384
42.1 41.0
26.3 25.4
489 478
53.6 62.5
27.7 29.2
PATRICIA VAN OPPEN
634
Table 2. Factor strengths of the PI as obtained in the Dutch normal sample in comparison with the factor strengths of the original Italian and American samules Factors (components, %) Dutch sample Females (n = 242) Males (n = 188) Total Origmal It&m sample Females (n = 478) Males (n = 489) Total American sample Total (n = 701)
I
2
3
4
Total I%)
19.6 22.8 20.4
12.4 15.2 13.0
14.9 16.5 15.2
6.1 14.3 9.2
33.5 37.7 34.4
10.6 10.7 Il.3
8.4 9.4 9.0
7.6 6.7 6.9
5.7 5.5 5.1
32.3 32.4 32.3
23.6
3.7
6.2
4.3
37.8
Factor I = impaired control of mental activities; 2 = becoming contaminated; 3 = checking behaviours; and 4 = urges and worries of losing control.
Table 2 provides a survey of the strengths of the 4 factors in the Italian (Sanavio, 1988), the American (Sternberger & Burns, 1990b) and the Dutch samples. The total amount of variance which is explained by the 4 factors conjointly is also presented in Table 2. There were hardly any differences between the total percentage explained variance for the respective samples. The strength of the 4 factors separately were higher in the Dutch sample than those found in the original sample. Comparison of the Dutch data and the American data showed that factor 1 of the American sample explained more of the variance than in the Dutch sample. The remaining 3 factors explained more variance in the Dutch than in the American sample. However, the data from the American sample was obtained by a principal component analysis. Because of the correlation among the factors, the total amount of variance explained in the Dutch sample is not identical to the sum of the 4 factors. Factor correlations for the present sample ranged from 0.22 to 0.61. These data are presented in Table 3. Reliability Nunnally (1978) holds that a minimum Cronbach’s c1 value of 0.70 is sufficient for research purposes. Table 4 presents Cronbach’s LYSfor each factor. These were found to be satisfactory, except for the subscale 4 (Urges and worries of losing control over motor behaviours), especially for females. Cronbach’s MS of the Italian and American samples are also given in Table 4. The present findings are in line with the American sample except for factor 4. Unfortunately, our data cannot be compared with the data of the Italian sample because the txs of the subscales were not reported. Test-retest reliabilities were obtained from the group Ss who were willing to participate in the follow-up. Test-retest correlations for the 8-week interval (Spearman’s p) are shown in Table 5. Coefficients between 0.60 and 0.90 are appropriate values for stability over time. According to this criterium all PI-subscales show stability over an 8-week interval, apart from subscale 1 for the male sample. This subscale is just below the required level. The results of the Spearman’s p of the total scale are comparable with the test-retest correlation for the 30-day interval of the Italian sample (0.78 for males and 0.83 for females) (Sanavio, 1988). Convergent and divergent validity To determine with a number
the convergent and divergent validity of the PI, the subscale scores were correlated of other questionnaires. The following hypotheses were formulated:
(1) High correlations were expected between similar measures, i.e. (a) between the PI contamination scale and the MOCI cleaning scale, (b) between the PI and the MOCI Table 3. Correlations between the 4 factors Factor I, 2, 3, 4.
Impaired control Becoming contaminated Checking Urees and worries
I
2
3
4
I .oo 0.51 0.61 0.45
1.00 0.44 0.22
I .oo 0.33
1.00
Obsessions
and compulsions
635
Table 4. The internal consistency of the PI (Cronbach’s coefficient a) Factor
Dutch sample Males (n = 188) Females (n = 242) Total (n = 430) Italian sample Males (n = 489) Females (n = 478) American sample Total (n = 701)
I (17 items)
2 (II items)
3 (8 items)
4 (7 items)
Total (60 items)
0.89 0.90 0.90
0.80 0.83 0.82
0.87 0.86 0.86
0.68 0.46 0.57
0.94 0.93 0.94 0.90 0.94
0.89
0.81
0.87
0.77
0.94
For description of factors see legend to Table 2
checking scale, (c) between the PI and the MOCI total scale, and (d) between the SCL-90-R obsessive-compulsive scale and the PI total score (Sanavio, 1988; Sternberger & Burns, 1990b). (2) A substantially positive correlation was expected between subscales which measure depression, anxiety, and neuroticism (Marks, 1987), i.e. (a) between the PI and the SCI-90-R Depression scale, (b) between PI and the FQ Anxiety-Depression scale, and (c) between the PI and the EPQ-R Neuroticism scale. (3) A substantially positive correlation was expected between the PI and SCL-90-R Hostility scale on the one hand and PI and SCL-90-R Sensitivity scale on the other (Millar, 1983; Niler & Beck, 1989). (4) No substantial correlation was expected between the PI and the EPQ-R Psychoticism scale on the one hand and between the PI and the EPQ-R Social Desirability scale on the other (Sanavio, 1988; Sternberger & Burns, 1990b). Table 6 presents the correlations, corrected for attenuation (Nunnally, 1978). This correction for attenuation is an estimate of the correlation if two variables were made perfectly reliable. Evidence in support of the first hypothesis was found. The correlations, corrected for attenuation (Ra) between the subscale checking of the PI and the subscale checking of the MOCI (Ra = 0.84) on the one side and between the subscale contamination of the PI and cleaning of the MOCI (Ra = 0.74) on the other side, were found to be substantial. As to the total scale, high correlations were found between the PI and the SCL-90-R Obsessive-Compulsive scale (Ra = 0.72) and between the PI and the MOCI (Ra = 0.74). Further, as expected a significant positive relationship was found between the PI and: (a) the SCL-90-R Depression scale (Ra = 0.61), (b) the FQ Anxiety-Depression scale (Ra = 0.67), (c) the EPQ-R subscale Neuroticism (Ra = 0.60), (d) the SCL-90-R subscales Sensitivity (Ra = 0.68), and (e) Hostility (Ra = 0.54), thus supporting hypotheses (2) and (3). Finally, low correlations were found between all PI scales on the one hand and the EPQ-R Psychoticism (-0.14), Extraversion (-0.28) and Social Desirability scales (- 0.01) on the other hand. These findings are in line with hypothesis (4). DISCUSSION One of the purposes of the present study was to examine the generalizability of the dimensional structure underlying the PI (Sanavio, 1988). Generally, the results support the 4 factor solution found by Sanavio (1988). The 4 factors were replicated in this sample. Substantial
Table 5. Test-retest reliability coefficients (8-week interval) (Spearman’s p) for PI scales PI I, Impaired control 2, Becoming contaminated 3, Checking 4, Urges and worries Total
Females (n = I 12)
Males (n = 84)
Total (n = 196)
0.77 0.83 0.74 0.77 0.82
0.57 0.64 0.67 0.74 0.71
0.73 0.76 0.71 0.76 0.79
636
PATRICIA VAN OPPEN Table 6. Correlations (pearsonian type), cow&cd for attenuation (Ra) between subscales of the PI with the MOCI, the SCL-90-R Depression, Sensitivity, Obsessive-Compulsive, and Hostility scale, the subscales of the EPO-R, the subscales of the FO, and the subscales of the PI PI Cronbach MOCI Total Checking Doubting Cleaning SCL-90-R Obsessive-compulsive Depression Sensitivity Hostility
FQ
Anxietydepression Social fears Agoraphobia Blood-injury fears EPQ-R Neuroticism Social desirability Psychoticism Extraversion N=408. The s&e Tabie 2.
reliabilities
2 Ra (0.82)
a
3 Ra (0.86)
4 Ra (0.57)
Total Ra (0.94)
(0.79) (0.67) (0.62) (0.52)
O+S n+S g+c? O+S
0.67 0.66 0.66 0.36
0.55 0.50 0.3 I 0.74
0.65 0.84 0.4 I 0.33
0.24
0.74 0.77 0.61 0.50
(0.84) (0.93) (0.92) (0.74)
?+6 9+6 Y+6 P+$
0.78 0.71 0.76 0.61
0.34 0.24 0.35 0.21
0.50 0.36 0.42 0.30
0.61 0.61 0.66 0.61
0.72 0.61 0.68 0.54
(0.86) (0.76) (0.75) (0.68)
n+d Y+$ E+3 5j+6
0.78 0.67 0.58 0.46
0.25 0.38 0.36 0.34
0.44 0.36 0.35 0.29
0.71 0.55 0.39 0.40
0.67 0.61 0.54 0.45
(0.84) (0.70) (0.50) (0.80)
FfC? P+$ O+$ Y+&
0.64 -0.07 -0.13 -0.32
0.29 0.15 -0.09 -0.10
0.43 0.05 -0.12 -0.20
0.58 -0.34 -0.01 - 0.28
0.60 -0.01 -0.14 -0.28
are given in parentheses.
For description
0.50 0.49
0.50
of factors
see legend to
correlations between the 4 factors are found. However, these are not such that the factors are interchangeable. A second aim pertained to determine the internal consistency and the test-retest reliability over an g-week interval of the 4 PI subscales. Most of the results were in line with the psychometrics demands. Besides Cronbach’s a of factor 4 for female Ss, all subscales of the PI were found to have good internal consistency. Further the PI subscales were found to have satisfactory test-retest reliability over an S-week interval, although the reliability was slightly less for factor 1 of the male sample. The third aim was to assess the convergent and divergent validity of the PI. As expected substantial correlations were found between related scales of the PI and the MOCI. The substantial correlation between the total PI scores and the two subscales of the SCL-90-R, Sensitivity and Hostility, are in line with the findings reported in Millar (1983). As Millar noted there exists a close relationship between obsessional complaints and negative evaluation of others and outwardly directed anger. The substantial correlations of the PI with the SCL-90-R Depression subscale and the Anxiety-Depression subscale of the FQ corroborate the findings that OCD is related to depressed mood (reviewed in Marks, 1987). The expected low correlations between all PI scales on the one hand and the EPQ-R Psychoticism, Extraversion and Social Desirability scaies on the other hand were also found. Interestingly, the mean score of the PI in the present study (mean = 27.86) differs from the mean score of the American sample (mean = 41.33) and even more so from the Italian sample (mean = 58.00). One could argue that the sample in this study shows a low incidence of obsessive-compulsive complaints compared with the total Dutch population. However, this is in contradiction with the findings that the mean score of the MOCI in this study is even higher than the mean scores of the MOCI for Dutch normals in the study of Kraaijkamp et al. (1988) (mean = 4.8, SD = 3.4 vs mean = 3.9, SD = 2.9). Actually, in terms of scores on the MOCI the sample appears to be comparable to a British normal sample: the mean score for the MOCI in the Reynolds and Salkovskis (1991) study was 4.96 (SD = 5.21). Further studies are needed to investigate the differences in obsessive-compulsive complaints across nations and cultures. The PI seems particularly useful for this purpose given its cross-national equivalence in terms of factor structure and psychometric qualifications. The mean total scale score of the PI shows no significant difference between males and females, but there is a trend that females scored higher than males. This finding is consistent with the prevalence rate of OCD among women, which was found to be slightly higher than for males
Obsessions
631
and compulsions
(Myers, Weissman, Tischeler, Holzer, Leaf, Orvaschel, Anthony, Boyd, Burke, Dramer & Stoltzman, 1984), and with studies into fears, in which females systematically report more fears than males (Arrindell, Emmelkamp & van der Ende, 1984). A significant gender difference emerged on two subscales: (1) impaired control of mental activities and (2) becoming contaminated. The gender difference found on the subscale becoming contaminated is in line with the finding that more females than males have cleaning rituals (Hoekstra, Visser & Emmelkamp, 1989). In sum, the present study provides evidence for the factor structure and reliability of PI in a Dutch sample, and suggests that the PI may be used as a research instrument cross-nationally. For researchers as well as clinicians the PI can be a useful measure because it includes items about obsessions and urges, in contrast with other questionnaires. Although the convergent and divergent validity was found to be good further studies are needed to demonstrate its discriminant validity. Further, the differences in obsessive-compulsive complaints across various nations are of great theoretical interest and deserves further study. Acknowledgements-The manuscript and Laura
author wishes to thank Paul Emmelkamp for his insightful comment van Bergen for her help with a part of the statistical analysis.
on an earlier draft
of the
REFERENCES Arrindell, W. A. & Ettema, H. (1986). XL-90. Een multidimensionele psychopathologic indicator. Lisse: Swets and Zeitlinger. Arrindell, W. A., Emmelkamp, P. M. G. & van den Ende, J. (1984). Phobic dimensions: I. Reliability and generalizability across samples, gender and nations. The Fear Survey Schedule (FSS-III) and the Fear Questionnaire (FQ). AdLances in Behavior Research and Therapy, 6, 207-254. Camstra, H. (1985). Pekon, een Pascal programma voor CDL-computers. Technical report, University of Groningen, The Netherlands. Chan, D. W. (1990). The Maudsley Obsessional-Compulsive Inventory: a psychometric investigation on Chinese normal subjects. Behaviour Research and Therapy, 28, 413420. Cooper, J. (1970). The Leyton Obsessional Inventory. Psychological Medicine, 1, 4844. Derogatis, L. R. (1977). XL-90: Administration, scoring andprocedures manual-Ifor the Revised version Baltimore, MD: Johns Hopkins University School of Medicine, Clinical Psychometrics Research Unit. Eysenck, H. J. & Eysenck, S. B. G. (1983). Recent advances in the cross-cultural study of personality. In Butcher, J. N. & Speilberger, C. D. (Eds), Advances in personalify assessment. 2, Hillsdale, NJ: LEA. Goodman, W. K. & Price, L. H. (1990). Rating scales for obsessive-compulsive disorder. In Jenike, M. A., Baer, L. & Minichiello, W. E. (Eds.) Obsessive-compulsive disorders: Theory and management. (2nd Edn). Year book medical publishers. Goodman, W. K., Price, L. H., Rasmussen, S. A., Mazure, C., Fleischmann, R. L., Hill, C. L., Heninger, G. R. & Charney, D. S. (1989). The Yale-Brown Obsessive scale I. Development, use, and reliability. Archives of General Psychiafry, 46, 1006-1011. Hodgson, R. J. & Rachman, S. (1977). Obsessional-compulsive complaints. Behaviour Research and Therapy, 15, 389-395. Hoekstra, R. J., Visser, S. & Emmelkamp, P. M. G. (1989). A social learning formulation of the etiology of obsessive-compulsive disorders. In Emmelkamp, P. M. G., Everaerd, W. T. A. M., Kraaimaat, F. W. &van Son M. J. M. (Eds), Fresh perspectives on anxiety disorders. Lisse: Swets and Zeitlinger. Kozak, M. J., Foa, E. B. SC McCarthy, P. R. (1988). Obsessive-compulsive disorder. In Last, C. G. & Hersen, M. (Ed.), Handbook of anxiefy disorders. New York: Pergamon Press. Kraaijkamp, H. J. M.. Emmelkamp, P. M. G. & Hout, van den M. A. (1988). The Maudsley Obsessional-Compulsive Inventory: Reliability and validity. Unpublished manuscript. Marks, I. M. (1987). Fears, phobias and rituals. Panic, anxie?y and their disorders. New York: Oxford University Press. Marks, I. M. & Matthews. A. M. (1979). Brief standard self-rating I for .uhobic uatients. Behauiour Research and Theraov. ‘, 17, 5948. Millar, D. G. (1983). Hostile emotion and obsessional neurosis. Psychological Medicine, 13, 813-819. Myers, J. K., Weissman, M. M., Tischler, G. L., Holzer, C. E., Leaf, P. J., Orvaschel, H., Anthony, J. C., Boyd, J. H., Burke, J. D., Kramer, M. & Stoltzman, R. (1984). Six-month prevalence of psychiatric disorders in three communities. Archives of General Psychiatry, 41, 959-967. Niler, E. R. & Beck, S. J. (1989). The relationship among guilt, dysphoria, anxiety and obsessions in a normal population. Behaviour Therapy and Research, 27, 213-220. Nunnally, J. C. (1978). Psychometric theory (2nd Edn). New York: McGraw-Hill. Philpott, R. (1975). Recent advances in the behavioral measurement of obsessional illness: Difficulties common to these and other instruments. Scottish Medical Journal, 20. 3340. Reynolds, M. & Salkovskis, P. M. (1991). The relationship among guilt, dysphoria, anxiety and obsessions in a normal population-an attempted replication. Behaviour Research and Therapy, 29, 259-265. Sanavio, E. (1988). Obsessions and compulsions: the Padua Inventory. Behauiour Research and Therapy, 26, 167-177. Sternberger, L. B. & Burns, G. L. (1990a). Maudsley Obsessional-Compulsive Inventory; obsessions and compulsions in a nonclinical sample. Behaviour Research and Therapy, 28, 337-340. Sternberger, L. G. & Burns, G. L. (1990b). Obsessions and compulsions: psychometric properties of the Padua Inventory with an American college population. Behaviour Research and Therapy, 28, 341-345. Ten Berge, J. M. F. (1986) Rotation to perfect congruence and the cross-validation of component weights across populations. Multirrariate Behavioral Research, 21, 4144.
Behau.Res.Ther.Vol.30,No.6,pp.631437, 1992 Printed in Great Britain. All rights reserved
OBSESSIONS AND COMPULSIONS: DIMENSIONAL STRUCTURE, RELIABILITY, CONVERGENT AND DIVERGENT VALIDITY OF THE PADUA INVENTORY PATRICIA Free University,
Faculty
VAN OPPEN
of Medicine, Department of Psychiatry at the Amsterdam Valeriusplein 9, 1075 BG Amsterdam, The Netherlands (Received 22 November
Psychiatric
Centre,
1991)
Summary-This study presents data on dimensional structure, reliability, convergent and divergent validity of the Padua Inventory (PI). In a sample (n = 430) of normal Dutch subjects. The dimensional structure and the strength of the factors were comparable to those found in the Italian sample. The reliability of the PI was found to be satisfactory. As hypothesized substantial correlations were found between the PI and related scales of the Maudsley Obsessive-Compulsive Inventory (MOCI) and between the PI and the subscales Sensitivity, Hostility and Depression of the revised version of the Symptom Checklist. Low correlations were found between the PI on the one side and the Eysenck Personality Ouestionnaire revised Extraversion. Psvchoticism and Social Desirabilitv scale on the other side. Finallv. the mean score of the PI differs across the Italian, American and Dutch samples. This is of theoretical interest and deserves further study.
INTRODUCTION
of obsesRecent reviews of the psychometric features of rating scales for the assessment siveecompulsive disorder (OCD) and symptoms (Kozak, Foa & McCarthy, 1988; Goodman & Price, 1990; Goodman, Price, Rasmussen, Mazure, Fleischmann, Hill, Henninger & Charney, 1989) point to the shortcomings of the existing rating scales, including lack of specificity for obsessiveecompulsive symptoms, confusion of trait with state measures, examination of only certain types of obsessions and compulsions, and inadequate analysis of or poor scale psychometric properties (e.g. lack of factor constancy, insufficient sensitivity to detect treatment outcome, low convergent validity). There is also a lack of questionnaires which delineate obsessions and covert rituals. Of the existing self-report inventories, the Leyton Obsessional Inventory (LOI; Cooper, 1970), the Maudsley Obsessive-Compulsive Inventory (MOCI; Hodgson & Rachman, 1977) and the Compulsive Activity Checklist (CAC; Philpott, 1975) are the three most widely used self-rating scales. For the MOCI and the CAC only two strong factors were found: contamination (washing) and checking (Chan, 1990; Hodgson & Rachman, 1977; Kraaijkamp, Emmelkamp & van der Hout, 1988; Sternberger dz Burns, 1990a). More recently, a new self-report inventory, termed the Padua Inventory (PI; Sanavio, 1988), has been described to hold promise as a measure which will allow an accurate quantification of OCD symptoms, since it is the only self-report measure which includes strong obsessional dimensions as distinct from compulsive dimensions (Sanavio, 1988; Sternberger & Burns, 1990b). The PI was developed in Italian by Sanavio (1988) to obtain the most important and frequent types of obsessional complaints. The PI contains not only items which measure intrusive thoughts, doubts, checking and cleaning behaviours, but also items pertaining to senseless or unacceptable urges, repetitive thinking about low-probability dangers, recurrent repugnant images etc. This inventory is composed of statements gathered by interviews of obsessional patients and studies with normals as well as neurotic and obsessive-compulsive patients. Factor analysis of data of 967 normal adult Ss resulted in a 4 factor solution: (1) impaired control of mental activities; (2) becoming contaminated; (3) checking behaviours; and (4) urges and worries of losing control over motor behaviours (Sanavio, 1988). Furthermore, in a sample of students, the PI General scale was found to correlate substantially with the MOCI (0.70), and the LO1 (0.71 with Symptom and 0.66 with Trait scales), and less strongly so, at clearly lower magnitudes, with non-homologous measures 631
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632
(e.g. Extraversion - 0.10, Psychoticism 0.09). Test-retest reliability of students (during a 30-day interval) and internal consistency of the scale were found to be satisfactory. Sternberger and Burns (1990b) examined the psychometric properties of the PI with an American college population. Exploratory factor analysis suggested a 4 factor solution which was described to be very similar to that found in the original Italian study of the PI. Internal consistencies for the subscales, according to Sanavio (1988), were reported to be good (range of as: 0.77-0.89). The present study was designed to investigate the generalizability of and to extend the findings of Sanavio (198X) and Sternberger and Burns (1990b) by studying the PI in a Dutch context using community volunteers as 5’s. Such an attempt seems useful for two reasons. First, with the availability of a standard, reliable and valid form of the PI in different countries, comparisons of patient data across research and treatment centres both within and across countries can be justifiably carried out. Second a standard form could be utilized for increasing our knowledge on similarities and differences in the cross-national incidence of obsessional symptoms. Specifically, the aims of the present study were 3-fold, namely to (a) investigate the cross-national stability of the dimensional structure underlying the PI (Sanavio, 1988), (b) establish the internal consistency and the test-retest reliability over an S-week interval of the different PI subscales, and (c) assess the convergent and divergent validity of the different PI scales. METHOD Subjects and procedwes
Participants in the present study were recruited by means of a mail survey. An at random taken sample (n = 1000) was acquired by a municipal office of a medium size municipality. Several questionnaires were mailed to the Ss, preceded by an initial covering letter in which the purpose of the two-stage follow-up survey was stated. The time frame between first and second testing was 8 weeks. Ss willing to participate in the follow-up study were asked either to state their names and addresses or to complete the questionnaires anonymously when unwilling to do so. A pre-addressed envelope stamped Return was enclosed to facilitate response. After deduction of the Ss who had moved or deceased the total sample consists of 961 5’s. One reminder letter was sent out at a fortnightly interval yielding a total response of 430 participants (45%). Of these 430 participants 191 Ss participated in the test-retest study. The sample (all Dutch citizens) consisted of 188 males (44%) and 242 females (56%). The sexes were comparable in terms of age: 40.59 yr (SD = 13.05, range: 18-68) and 38.47 yr (SD = 13.06, range: 18-65) respectively. With regard to their marital status 75% of the Ss were either married or cohabiting. Of all Ss 17% reported being unmarried and living without a partner, while 4% were divorced and 3% were widows/widowers. Almost one-tenth (9%) of the Ss followed only elementary school or less. More than one third (37%) did finish the advanced elementary education and one third (33%) completed modern (secondary) school. Another 19% had at least some college education. In terms of sexes, marital status and education this sample is a fairly good representative sample of the Dutch population. Measures
The following measures were completed: (1) The PI (Sanavio, 1988), consisting of 60 items: range O-240. (2) The MOCT (Wodgson & Rachman, 1977), a 30-item true-false self-report inventory. In the present study the total scale, the subscale washing, checking, and slowness were used. For a Dutch sample the ‘slowness’ subscale appeared to be less useful (Kraaijkamp et al., 1988). (3) The revised version of the Symptom Checklist (SCL-90-R; Derogatis, 1977), a multidimensional self-report inventory of current psychiatric symptoms; range 90-450. The Dutch version of the SCL-90-R provides scores on the dimensions: Agoraphobia, Somatization, Hostility, Depression, Sensitivity, Anxiety, Obsessive-Compulsive problems, and Sleep Disturbance (Arrindell & Ettema, 1986).
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(FQ; Marks & Matthews, 1979), consisting of 20 items, rated on (4) The Fear Questionnaire a 9-point continuum. The FQ yields four subscores: Agoraphobic fears, Social fears, Blood-Injury fears, and an Anxiety-Depression dimension. Questionnaire revised (EPQ-R; Eysenck & Eysenck, (5) The short-scale Eysenck Personality 1983) consisting of 48 yes-no questions. This questionnaire measures the personality dimensions of Neuroticism, Psychoticism, and Extraversion; in addition it results in a score for Social Desirability. Statistics The method for determining cross-national stability of the dimensional structure underlying the PI involved the comparison of factors (components) from other samples with those obtained in the original sample on the basis of ‘perfectly-congruent weights’ (Ten Berge, 1986). The purpose of this method is to determine recoverableness of components from an original study in a replication study with the same interpretations and to evaluate the amounts of variance they explain (Ten Berge, 1986). The matrix of components weights obtained in the original study were used to cross-validate these components in the replication study. Recoverableness can be defined in terms of amounts of variance explained. Therefore, the separate amounts of variance explained by each of any hypothetical factor in the replication study are of major interest, The percentage may vary from 0 to 100%. Besides the strength of each factor, Ten Berge’s approach advocates that the inter-correlations among factors be considered in the interpretative process as well. The VARIMAX rotated 4-factor principal solution of normal Ss (n = 967) reported in Sanavio (1988) was used as the theoretical structure. Actual calculations involved were performed by using the Pekon (PErfect CONgruence) computer programme (Camstra, 1985). Cronbach’s c( coefficient served as measure of internal consistency. To assess convergent and divergent validity, correlations among PI subscales and other scales were determined. For the test-retest reliability Spearman correlations were calculated.
RESULTS
The means and standard deviations of the total PI scores are given in Table 1. There was no significant difference between females and males [t (428) = - 1.78, P = 0.08 NS]. But, there was a significant gender difference on two subscales: (1) impaired control of mental activities [t(428) = -3.26, P = O.OOl], and (2) becoming contaminated [t(426.61) = -2.17, P = 0.031. The female and male mean scores in this study differed from the mean scores in the Italian as well as in the American sample. Dimensional
structure
Pekon determines the strength of the loadings on the original factors in the new material. All items loaded on the respective factors (at least 0.49). Except for item 57 (“I feel I have to make special gestures or walk in a certain way”) which loaded nearly equal on factor (1) (0.37) and factor (4) (0.39), and for item 60 (“I invent useless worries about germs and diseases”) which loaded equal on factor (1) (0.46) and factor (2) (0.46).
Table I. PI scores: means and standard deviations of the Italian, American and Dutch samples
Dutch sample Males Females American sample Males Females Italian sample Males Females
n
Mean
SD
188 242
25.8 29.4
20.8 20.7
294 384
42.1 41.0
26.3 25.4
489 478
53.6 62.5
27.7 29.2
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Table 2. Factor strengths of the PI as obtained in the Dutch normal sample in comparison with the factor strengths of the original Italian and American samules Factors (components, %) Dutch sample Females (n = 242) Males (n = 188) Total Origmal It&m sample Females (n = 478) Males (n = 489) Total American sample Total (n = 701)
I
2
3
4
Total I%)
19.6 22.8 20.4
12.4 15.2 13.0
14.9 16.5 15.2
6.1 14.3 9.2
33.5 37.7 34.4
10.6 10.7 Il.3
8.4 9.4 9.0
7.6 6.7 6.9
5.7 5.5 5.1
32.3 32.4 32.3
23.6
3.7
6.2
4.3
37.8
Factor I = impaired control of mental activities; 2 = becoming contaminated; 3 = checking behaviours; and 4 = urges and worries of losing control.
Table 2 provides a survey of the strengths of the 4 factors in the Italian (Sanavio, 1988), the American (Sternberger & Burns, 1990b) and the Dutch samples. The total amount of variance which is explained by the 4 factors conjointly is also presented in Table 2. There were hardly any differences between the total percentage explained variance for the respective samples. The strength of the 4 factors separately were higher in the Dutch sample than those found in the original sample. Comparison of the Dutch data and the American data showed that factor 1 of the American sample explained more of the variance than in the Dutch sample. The remaining 3 factors explained more variance in the Dutch than in the American sample. However, the data from the American sample was obtained by a principal component analysis. Because of the correlation among the factors, the total amount of variance explained in the Dutch sample is not identical to the sum of the 4 factors. Factor correlations for the present sample ranged from 0.22 to 0.61. These data are presented in Table 3. Reliability Nunnally (1978) holds that a minimum Cronbach’s c1 value of 0.70 is sufficient for research purposes. Table 4 presents Cronbach’s LYSfor each factor. These were found to be satisfactory, except for the subscale 4 (Urges and worries of losing control over motor behaviours), especially for females. Cronbach’s MS of the Italian and American samples are also given in Table 4. The present findings are in line with the American sample except for factor 4. Unfortunately, our data cannot be compared with the data of the Italian sample because the txs of the subscales were not reported. Test-retest reliabilities were obtained from the group Ss who were willing to participate in the follow-up. Test-retest correlations for the 8-week interval (Spearman’s p) are shown in Table 5. Coefficients between 0.60 and 0.90 are appropriate values for stability over time. According to this criterium all PI-subscales show stability over an 8-week interval, apart from subscale 1 for the male sample. This subscale is just below the required level. The results of the Spearman’s p of the total scale are comparable with the test-retest correlation for the 30-day interval of the Italian sample (0.78 for males and 0.83 for females) (Sanavio, 1988). Convergent and divergent validity To determine with a number
the convergent and divergent validity of the PI, the subscale scores were correlated of other questionnaires. The following hypotheses were formulated:
(1) High correlations were expected between similar measures, i.e. (a) between the PI contamination scale and the MOCI cleaning scale, (b) between the PI and the MOCI Table 3. Correlations between the 4 factors Factor I, 2, 3, 4.
Impaired control Becoming contaminated Checking Urees and worries
I
2
3
4
I .oo 0.51 0.61 0.45
1.00 0.44 0.22
I .oo 0.33
1.00
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and compulsions
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Table 4. The internal consistency of the PI (Cronbach’s coefficient a) Factor
Dutch sample Males (n = 188) Females (n = 242) Total (n = 430) Italian sample Males (n = 489) Females (n = 478) American sample Total (n = 701)
I (17 items)
2 (II items)
3 (8 items)
4 (7 items)
Total (60 items)
0.89 0.90 0.90
0.80 0.83 0.82
0.87 0.86 0.86
0.68 0.46 0.57
0.94 0.93 0.94 0.90 0.94
0.89
0.81
0.87
0.77
0.94
For description of factors see legend to Table 2
checking scale, (c) between the PI and the MOCI total scale, and (d) between the SCL-90-R obsessive-compulsive scale and the PI total score (Sanavio, 1988; Sternberger & Burns, 1990b). (2) A substantially positive correlation was expected between subscales which measure depression, anxiety, and neuroticism (Marks, 1987), i.e. (a) between the PI and the SCI-90-R Depression scale, (b) between PI and the FQ Anxiety-Depression scale, and (c) between the PI and the EPQ-R Neuroticism scale. (3) A substantially positive correlation was expected between the PI and SCL-90-R Hostility scale on the one hand and PI and SCL-90-R Sensitivity scale on the other (Millar, 1983; Niler & Beck, 1989). (4) No substantial correlation was expected between the PI and the EPQ-R Psychoticism scale on the one hand and between the PI and the EPQ-R Social Desirability scale on the other (Sanavio, 1988; Sternberger & Burns, 1990b). Table 6 presents the correlations, corrected for attenuation (Nunnally, 1978). This correction for attenuation is an estimate of the correlation if two variables were made perfectly reliable. Evidence in support of the first hypothesis was found. The correlations, corrected for attenuation (Ra) between the subscale checking of the PI and the subscale checking of the MOCI (Ra = 0.84) on the one side and between the subscale contamination of the PI and cleaning of the MOCI (Ra = 0.74) on the other side, were found to be substantial. As to the total scale, high correlations were found between the PI and the SCL-90-R Obsessive-Compulsive scale (Ra = 0.72) and between the PI and the MOCI (Ra = 0.74). Further, as expected a significant positive relationship was found between the PI and: (a) the SCL-90-R Depression scale (Ra = 0.61), (b) the FQ Anxiety-Depression scale (Ra = 0.67), (c) the EPQ-R subscale Neuroticism (Ra = 0.60), (d) the SCL-90-R subscales Sensitivity (Ra = 0.68), and (e) Hostility (Ra = 0.54), thus supporting hypotheses (2) and (3). Finally, low correlations were found between all PI scales on the one hand and the EPQ-R Psychoticism (-0.14), Extraversion (-0.28) and Social Desirability scales (- 0.01) on the other hand. These findings are in line with hypothesis (4). DISCUSSION One of the purposes of the present study was to examine the generalizability of the dimensional structure underlying the PI (Sanavio, 1988). Generally, the results support the 4 factor solution found by Sanavio (1988). The 4 factors were replicated in this sample. Substantial
Table 5. Test-retest reliability coefficients (8-week interval) (Spearman’s p) for PI scales PI I, Impaired control 2, Becoming contaminated 3, Checking 4, Urges and worries Total
Females (n = I 12)
Males (n = 84)
Total (n = 196)
0.77 0.83 0.74 0.77 0.82
0.57 0.64 0.67 0.74 0.71
0.73 0.76 0.71 0.76 0.79
636
PATRICIA VAN OPPEN Table 6. Correlations (pearsonian type), cow&cd for attenuation (Ra) between subscales of the PI with the MOCI, the SCL-90-R Depression, Sensitivity, Obsessive-Compulsive, and Hostility scale, the subscales of the EPO-R, the subscales of the FO, and the subscales of the PI PI Cronbach MOCI Total Checking Doubting Cleaning SCL-90-R Obsessive-compulsive Depression Sensitivity Hostility
FQ
Anxietydepression Social fears Agoraphobia Blood-injury fears EPQ-R Neuroticism Social desirability Psychoticism Extraversion N=408. The s&e Tabie 2.
reliabilities
2 Ra (0.82)
a
3 Ra (0.86)
4 Ra (0.57)
Total Ra (0.94)
(0.79) (0.67) (0.62) (0.52)
O+S n+S g+c? O+S
0.67 0.66 0.66 0.36
0.55 0.50 0.3 I 0.74
0.65 0.84 0.4 I 0.33
0.24
0.74 0.77 0.61 0.50
(0.84) (0.93) (0.92) (0.74)
?+6 9+6 Y+6 P+$
0.78 0.71 0.76 0.61
0.34 0.24 0.35 0.21
0.50 0.36 0.42 0.30
0.61 0.61 0.66 0.61
0.72 0.61 0.68 0.54
(0.86) (0.76) (0.75) (0.68)
n+d Y+$ E+3 5j+6
0.78 0.67 0.58 0.46
0.25 0.38 0.36 0.34
0.44 0.36 0.35 0.29
0.71 0.55 0.39 0.40
0.67 0.61 0.54 0.45
(0.84) (0.70) (0.50) (0.80)
FfC? P+$ O+$ Y+&
0.64 -0.07 -0.13 -0.32
0.29 0.15 -0.09 -0.10
0.43 0.05 -0.12 -0.20
0.58 -0.34 -0.01 - 0.28
0.60 -0.01 -0.14 -0.28
are given in parentheses.
For description
0.50 0.49
0.50
of factors
see legend to
correlations between the 4 factors are found. However, these are not such that the factors are interchangeable. A second aim pertained to determine the internal consistency and the test-retest reliability over an g-week interval of the 4 PI subscales. Most of the results were in line with the psychometrics demands. Besides Cronbach’s a of factor 4 for female Ss, all subscales of the PI were found to have good internal consistency. Further the PI subscales were found to have satisfactory test-retest reliability over an S-week interval, although the reliability was slightly less for factor 1 of the male sample. The third aim was to assess the convergent and divergent validity of the PI. As expected substantial correlations were found between related scales of the PI and the MOCI. The substantial correlation between the total PI scores and the two subscales of the SCL-90-R, Sensitivity and Hostility, are in line with the findings reported in Millar (1983). As Millar noted there exists a close relationship between obsessional complaints and negative evaluation of others and outwardly directed anger. The substantial correlations of the PI with the SCL-90-R Depression subscale and the Anxiety-Depression subscale of the FQ corroborate the findings that OCD is related to depressed mood (reviewed in Marks, 1987). The expected low correlations between all PI scales on the one hand and the EPQ-R Psychoticism, Extraversion and Social Desirability scaies on the other hand were also found. Interestingly, the mean score of the PI in the present study (mean = 27.86) differs from the mean score of the American sample (mean = 41.33) and even more so from the Italian sample (mean = 58.00). One could argue that the sample in this study shows a low incidence of obsessive-compulsive complaints compared with the total Dutch population. However, this is in contradiction with the findings that the mean score of the MOCI in this study is even higher than the mean scores of the MOCI for Dutch normals in the study of Kraaijkamp et al. (1988) (mean = 4.8, SD = 3.4 vs mean = 3.9, SD = 2.9). Actually, in terms of scores on the MOCI the sample appears to be comparable to a British normal sample: the mean score for the MOCI in the Reynolds and Salkovskis (1991) study was 4.96 (SD = 5.21). Further studies are needed to investigate the differences in obsessive-compulsive complaints across nations and cultures. The PI seems particularly useful for this purpose given its cross-national equivalence in terms of factor structure and psychometric qualifications. The mean total scale score of the PI shows no significant difference between males and females, but there is a trend that females scored higher than males. This finding is consistent with the prevalence rate of OCD among women, which was found to be slightly higher than for males
Obsessions
631
and compulsions
(Myers, Weissman, Tischeler, Holzer, Leaf, Orvaschel, Anthony, Boyd, Burke, Dramer & Stoltzman, 1984), and with studies into fears, in which females systematically report more fears than males (Arrindell, Emmelkamp & van der Ende, 1984). A significant gender difference emerged on two subscales: (1) impaired control of mental activities and (2) becoming contaminated. The gender difference found on the subscale becoming contaminated is in line with the finding that more females than males have cleaning rituals (Hoekstra, Visser & Emmelkamp, 1989). In sum, the present study provides evidence for the factor structure and reliability of PI in a Dutch sample, and suggests that the PI may be used as a research instrument cross-nationally. For researchers as well as clinicians the PI can be a useful measure because it includes items about obsessions and urges, in contrast with other questionnaires. Although the convergent and divergent validity was found to be good further studies are needed to demonstrate its discriminant validity. Further, the differences in obsessive-compulsive complaints across various nations are of great theoretical interest and deserves further study. Acknowledgements-The manuscript and Laura
author wishes to thank Paul Emmelkamp for his insightful comment van Bergen for her help with a part of the statistical analysis.
on an earlier draft
of the
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