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Psychometric properties of the Padua Inventory in a sample of Japanese university students
Personality and Individual Differences 43 (2007) 1113–1123 www.elsevier.com/locate/paid
Psychometric properties of the Padua Inventory in a sample of Japanese university students Akio Wakabayashi
a,b,*
, Tadashi Aobayashi
a
a b
Department of Psychology, Chiba University, 1-33 Yayoi-cho, Inage, Chiba 263-8522, Japan Autism Research Centre, Department of Psychiatry, University of Cambridge, Douglas House, 18b Trumpington Road, Cambridge CB2 2AH, UK Received 6 April 2006; received in revised form 1 March 2007; accepted 6 March 2007 Available online 30 April 2007
Abstract The psychometric properties and factor structure of the Padua Inventory (PI), a measure of obsessive– compulsive phenomena, were examined in a non-clinical sample of 671 Japanese university students. Results showed high internal consistencies of both the total scale and its subscales in the Japanese sample. A factor analysis replicated a four-factor structure, consisting of three factors corresponding to those found in previous studies (‘Impaired control of mental activity’, ‘Being contaminated’ and ‘Checking behaviour’) and one factor (‘Impulsive thoughts’), which partly differed from that found previously. The total score of the PI correlated moderately with two Obsessive–Compulsive Personality Disorder (OCPD) measures, but two subscales of the PI did not show a correlation with OCPD. Results of a multiple regression analysis revealed the PI did not explain the degree of OCPD traits well, suggesting the PI measures OCD traits better than OCPD in non-clinical samples. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Obsessive–Compulsive Disorder (OCD); Obsessive–Compulsive Personality Disorder (OCPD); Padua Inventory; Non-clinical group; Factor structure
*
Corresponding author. Address: Department of Psychology, Chiba University, 1-33 Yayoi-cho, Inage, Chiba 2638522, Japan. E-mail address: [email protected] (A. Wakabayashi). 0191-8869/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.paid.2007.03.004
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1. Introduction The central features of obsessive–compulsive disorder (OCD) are unwanted and intrusive thoughts, impulses, or images that cause striking distress or anxiety accompanied by compulsive or ritual behaviours (DSM-IV-TR; APA, 2000). While the prevalence rate of OCD is about 2– 3% of the general population (Antony, Downie, & Swinson, 1998), research has shown that obsessions are actually normally occurring phenomena in non-clinical people (Rachman & de Silva, 1978; Salkovskis & Harrison, 1984; Wells & Morrison, 1994). These findings suggest OCD characteristics are more common than previously believed, and have led to several analogue (continuum hypothesis) studies of OCD in recent decades (for example, Burns, Formea, Keortge, & Sternberger, 1995). Although several measurement tools exist for OCD, the Padua Inventory (PI) (Sanavio, 1988) is one of the most frequently used instruments to measure obsessive–compulsive tendency in both clinical and non-clinical samples. The PI is a self-report inventory that assesses the degree of disturbance or difficulty that 60 different thoughts and behaviours engender for the individual. Sanavio (1988) reported results of a study in the Italian population showing the PI has very good reliability and validity. Sternberger and Burns (1990) replicated the psychometric properties of the PI in American college-students samples, and confirmed almost identical psychometric properties and factor structures of the PI. Further support for the reliability and validity of the PI has emerged from studies in other countries (for example, Kyrios, Bhar, & Wade, 1996; MacDonald & de Silva, 1999; Van Oppen, Hoekstra, & Emmelkamp, 1995), including a pilot study of the PI in Japan which reported its factor structure and convergent validity with the Maudsley ObsessionalCompulsive Inventory (MOCI; Hodgson & Rachman, 1977; Sugiura & Tanno, 2000), although its sample size was not enough. These findings show the validity and factor structure of the PI is consistent across samples from different countries. The four-factor structure of the PI, by PCA with Varimax rotation method, has been commonly shown throughout several countries, although some differences exist in the content of these factors. This suggests that obsessions and compulsions, which represent the core symptoms in OCD, might differ between countries to some extent. For example, the items loading on Factor I, which were believed to be core characteristics of OCD, obtained in Italian samples found only two-thirds of the items in the corresponding factor extracted from an American samples. Although the diagnostic standard of OCD should be universally common, because it is based on international standards (DSM-IV-TR, 2000 and ICD-10, 1992), the pattern of obsessions and compulsions seen in non-clinical people likely differs between countries to some extent. This is because the thoughts and behaviours of people in various cultures are affected by different social norms and habits, which are characteristic to each country. For example, clinical characteristics such as ‘clean and tidy’ and ‘incompleteness and checking’, which are parts of core components in OCD, are more commonly seen in Japanese people in everyday life compared to other countries (Kasahara, 1976). This is because these behavioural tendencies are closely connected to the social norms and habits particular to the Japanese society. Therefore, some ‘traits’ involving obsessive– compulsive behaviours are found widely in the normal population, and it might cause the elevation of the PI score in a non-clinical sample in Japan. Like obsessive–compulsive traits, obsessive–compulsive personality traits are also disseminated widely in the normal population (Pollak, 1995). This suggests the obsessive–compulsive personality style is also understood as falling along a continuum of severity from an adaptive coping style
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to an exaggerated and maladaptive expression (Hollander & Wong, 1995). However, unlike other personality disorders that are seen as part of a spectrum disorder, from a clinical view OCPD is not currently seen in the same spectrum of OCD. From this perspective, OCPD and OCD are defined as separate and distinct disorders (McCullough & Maltsberger, 1996). In line with this idea, the majority of individuals with OCD do not meet the criteria for OCPD (APA, 2000). According to DSM-IV-TR the essential features of OCPD are a preoccupation with orderliness, perfectionism, and control at the expense of flexibility, openness, and efficiency. Individuals with OCPD force themselves and others to follow rigid moral principles and very high standards of performance, and are inclined to be severely self-critical. These individuals are also deferential to authority and rules, and insist on literal compliance, regardless of circumstances (APA, 2000).1 Although OCD and OCPD are diagnostically differentiated, there are common features between them. For example they both show certain similarities in checking behaviours and in doubtfulness (suspicious). On the other hand, most people with OCPD do not show obsessions of contamination or impulsive thoughts, which are commonly seen in OCD. Consequently, since OCD and OCPD are discriminated from one another at the clinical level, an interesting question emerges about how well the thoughts and behaviours of these constructs are differentiated in the normal population. This leads to a question of whether the PI best measures obsessive–compulsive traits found in OCD or those seen in OCPD. If the results obtained from the PI are not highly correlated to OCPD measures, this would suggest that PI measures reflect obsessive–compulsive traits in OCD in the normal population. From this we would hypothesise the existence of a spectrum for obsessive and compulsive behaviours, ranging from those seen in the normal population to extreme expressions in OCD. However, if the PI scores show better correlations with OCPD measures, it would suggest the PI has limited ability to discriminate the degree of the traits found in OCD from those in OCPD. The aim in this study is to examine the psychometric properties and factor structure of the PI in a large non-clinical Japanese sample. Additionally, we aim to investigate the relationship between the characteristics of OCD measured by the PI and those in OCPD measures seen in a non-clinical population. 2. Method 2.1. Participants The participants were 671 (381 males and 290 females) undergraduate students in various majors/courses in Chiba University. Their mean age was 19.1 (SD = 1.17: range 17–28 yr). 2.2. Measures The Padua Inventory Japanese version (PI-J): The PI (Sanavio, 1988) is a 60-item self-report inventory, which measures obsessions and compulsions. The PI is considered to measure the 1
The ICD-10 (WHO, 1992) has a category called Anankastic Personality Disorder (APD), which corresponds to the description of OCPD in DSM-IV-TR (APA, 2000). APD is characterized by doubt, perfectionism, conscientiousness, checking and preoccupation with details, stubbornness, caution and rigidity.
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extent to which the obsessions and compulsions interfere with routine daily functioning. Each item, rated on a 5-point scale, measures the degree of disturbance caused by the thought or behaviour (0 = ‘not at all’ to 4 = ‘very much’). The total score is the sum of the 60 items. We used the Japanese version of the PI (Sugiura & Tanno, 2000), that was translated as accurately as possible from original descriptions under supervision by psychiatric specialists, with a back translation process. The OCPD screening 20: This 20-item inventory was developed to measure the degree of obsessive–compulsive personality traits based on the screening questions proposed by Zimmerman (1994) in the assessment of individuals with OCPD. This was converted to a 5-point rating scale, so that it could be directly compared to the PI. The PDQ-4:OCPD: The 8 items of the obsessive–compulsive personality disorders from the Personality Diagnostic Questionnaire 4th edition (PDQ-4; Hyler, 2004): The PDQ-4 is a 100-item, self-administered, true/false questionnaire that yields personality diagnoses consistent with the DSM-IV diagnostic criteria for the axis II disorders. We also modified this to a 5-point rating scale. 2.3. Procedure The PI-Japanese version (PI-J) was administered in groups during the classes of introductory psychology. The items of the PI-J were randomized in order to avoid continuing similar descriptions. Two hundreds and thirty two (134 males and 98 females) of the participants, who were randomly extracted, were asked to respond to two OCPD measures about two months after they took the PI-J.
3. Results 3.1. Fundamental psychometric properties of the PI-J All the questionnaires that had items with no response and had the same responses in all items were rejected. The mean total score of the PI-J was 72.7 (SD = 34.76) with a range of 2–179. The kurtosis was 0.42, and the skewness was 0.18. There was no significant difference between females (M = 72.7, SD = 35.15) and males (M = 72.6, SD = 34.24) (t(669) = 0.044, p = 0.965; two tailed). Cronbach’s alpha coefficient was calculated as an index of consistency in all items and to be 0.95. 3.2. Factor structure First, in order to compare with the earlier studies (Sanavio, 1988; Sternberger & Burns, 1990), a principal components analysis with Varimax rotation method was used to investigate the factor structure of the PI. Five factors had eigenvalues above 1.0. A plot of the eigenvalues (Kaiser criterion) and the pattern of factor loadings (Cattell’s scree) suggested a four-factor solution would be best. These four factors explained 36.1% of the variance. Then we also administered factor analysis by oblique rotation (Promax method), because it appeared the factors obtained might
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correlate highly with each other as components of obsessive–compulsive tendencies. The result of oblique rotation showed almost identical factor structure to the result of Varimax rotation. The items, which loaded on each factor with loadings 0.40 and over were identical in two factor structures. Table 1 shows the items loaded on the four factors. The inter-factors correlations in the oblique solution are shown in Table 2. Factor I, which corresponded to ‘Impaired control of mental activities’ named by Sanavio (1988), contained 14 items. Most items, which loaded on this factor, replicated the items which loaded on the corresponding factor in the studies by Sanavio (1988) and Sternberger and Burns (1990). Factor II (‘Urges and worries of losing control of motor behaviour’) contained 12 items. This factor contained 9 items, which loaded on the corresponding factors in Sternberger and Burns (1990), but only 6 of 12 items consistent with the corresponding factor in Sanavio (1988). Factor III (‘Being contaminated’), contained 13 items. The items, which loaded on this factor, replicated the items which load on the corresponding factor in the earlier studies (Sanavio, 1988; Sternberger & Burns, 1990). Factor IV (‘Checking behaviours’) contained 6 items. These items loaded on the corresponding factors in Sanavio (1988) and Sternberger and Burns (1990). Additionally, Confirmatory Factor Analysis (CFA) was performed on the 45 items employing the Amos 6.01 (Arbuckle, 2005). The estimation method was Maximum Likelihood. Each of 45 items was linked to each correspondent factor based on the result of the EFA. The result of a CFI yielded a v2939 ¼ 3225:41, with a CFI = 0.86, GFI = 0.90, and a RMSEA = 0.06. 3.3. Subscale scores and their reliabilities Subscale scores were calculated according to the results of the two factor analyses. The average scores of the subscales were as follows. The subscale-1 (‘Impaired control of mental activities’ or ‘Doubt for own acts which have been done’, which consisted of 14 items) was 25.9 (SD = 11.40), and Cronbach’s alpha was 0.88. The subscale-2 (‘Impulsive thoughts’, which consisted of 12 items) was 7.7 (SD = 7.38), and Cronbach’s alpha was 0.84. The subscale-3 (‘Being contaminated’, which consisted of 13 items) was 11.4 (SD = 8.75), and Cronbach’s alpha was 0.87. The subscale-4 (‘Checking behaviours’, which consisted of 6 items) was 9.6 (SD = 5.80), and Cronbach’s alpha was 0.84. There were no sex differences for the subscale scores (all ts < 1.00), except ‘‘Impulsive thoughts’’ in which males scored higher than females (t(669) = 2.497, p < 0.05). The intercorrelation among the subscale scores and correlations between four subscale scores and total score of the PI-J are shown in Table 3. 3.4. The relation and differences between the PI and two OCPD measures Psychometric properties of two OCPD measures used in this study were calculated. In the 20item OCPD screening questions, the mean score was 17.2 (SD = 11.98), and its Cronbach’s alpha was 0.83. In the 8-item OCPD scale in the PDQ-4, its mean score was 7.4 (SD = 5.33). Its Cronbach’s alpha was 0.68. There was no sex difference found for the mean scores in either scale (ts(230) = 0.215 and 0.213, n.s., respectively). The correlations between the Padua Inventory and two OCPD measures were shown in Table 4. The total score of the PI-J correlated moderately with two OCPD measures. In the subscales of the PI-J, ‘Impaired control of mental activity’ and ‘Checking behaviour’ correlated moderately
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Table 1 Factors and factor loadings for the Padua items Item Factor I: Impaired control of mental activities (Doubts about control of mental activities) 29. After doing something carefully, I still have the impression I have either done it badly or not finished it 33. Unpleasant thoughts come into my mind against my will and I cannot get rid of them 36. I imagine catastrophic consequences as a result of absent-mindedness or minor errors which I make 37. I think or worry at length about having hurt someone without knowing it 32. When I start thinking of certain things I become obsessed with them 45. In certain situations, I am afraid of losing my self-control and doing embarrassing things 26. I find it difficult to make decisions, even about unimportant matters 18. I have to do things several times before I think they are properly done 28. I have the impression that I will never be able to explain things clearly, especially when talking about important matters that involve me 11. When doubt and worries come to my mind, I cannot rest until I have talked them over with a reassuring person 44. When a thought or doubt comes into my mind, I have to examine it from all points of view and cannot stop until I have done so 12. When I talk, I tend to repeat the same things and the same sentence several times 13. I tend to ask people to repeat the same things to me several times consecutively even though I did understand what they said the first time 43. I worry about remembering completely unimportant things and make an effort not to forget them Factor II: Impulsive thoughts (Urges and worries of losing control of motor behaviour) 55. I am sometimes almost irresistibly tempted to steal something from the supermarket 48. At certain moments I am tempted to tear off my clothes in public 54. I sometimes have an impulse to steal other people’s belongings even if they are of no use to me 56. I sometimes have an impulse to hurt defenseless children or animals 46. When I look down from a bridge or a very high window, I feel an impulse to throw myself into space 49. While driving, I sometimes feel an impulse to drive the car into someone or something 35. My brain constantly goes its own way and I find it difficult to attend to what is happening around me 59. When I hear about a suicide or crime, I am upset for a long time and find it difficult to stop thinking about it 51. I get upset and worried at the sight of knives, daggers and other pointed objects 47. When I see a train approaching I sometimes think I could throw myself under its wheels 53. I sometimes feel the need to break or damage things for no reason 50. Seeing weapons excites me and makes me think violent thoughts Factor III: Being contaminated 8. I sometimes have to wash or clean myself simply because I think I may be dirty or contaminated 9. If I touch something I think is ‘contaminated’, I immediately have to wash or clean myself 7. I wash my hands more often and longer than necessary 60. I invent useless worries about germs and disease 5. I avoid using public toilets because I am afraid of disease and contamination
Loadings 0.638 (0.613) 0.616 (0.637) 0.583 (0.522) 0.580 0.572 0.565 0.526 0.517 0.488
(0.572) (0.609) (0.571) (0.473) (0.486) (0.505)
0.471 (0.511) 0.467 (0.428) 0.464 (0.463) 0.462 (0.446) 0.450 (0.427)
0.685 (0.701) 0.641 (0.667) 0.632 (0.647) 0.578 (0.622) 0.547 (0.583) 0.540 (0.539) 0.538 (0.509) 0.508 (0.488) 0.501 0.478 0.446 0.438
(0.479) (0.521) (0.452) (0.442)
0.633 (0.615) 0.585 0.580 0.573 0.567
(0.564) (0.547) (0.556) (0.543)
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Table 1 (continued) Item
Loadings
10. If an animal touches me, I feel dirty and immediately have to wash myself or change my clothing 14. I feel obliged to follow a particular order in dressing, undressing and washing myself 6. I avoid public telephones because I am afraid of contagion or disease 10. Before going to bed I have to hang up or fold my clothes in a special way 1. I feel my hands are dirty when I touch money 2. I think even slight contact with bodily secretions (perspiration, saliva, urine, etc.) may contaminate my clothes or somehow harm me 3. I find it difficult to touch an object when I know it has been touched by strangers or by certain people 15. Before going to sleep I have to do certain things in a certain order
0.537 (0.572) 0.535 0.509 0.508 0.500 0.447
(0.557) (0.501) (0.483) (0.570) (0.487)
0.437 (0.433) 0.427 (0.439)
Factor IV: Checking behaviours 20. I check and recheck gas and water taps and light switches after turning them off 22. I keep on checking forms, documents, checks, etc. in detail to make sure I have filled them in correctly 21. I return home to check doors, windows, drawers, etc. to make sure they are properly shut 23. I keep on going back to see that matches, cigarettes, etc. are properly extinguished 25. I check letters carefully many times before posting them 27. Sometimes, I am not sure I have done things which in fact I know I have done
0.659 (0.731) 0.654 (0.694) 0.620 0.573 0.496 0.483
(0.679) (0.603) (0.499) (0.473)
Note: Only loading >0.40 are shown by ‘Varimax’ (Promax) rotated solutions.
Table 2 Intercorrelations between four factors obtained in oblique solution Factors
I (Impaired control)
II (Impulsive)
III (Contaminated)
II (Impulsive) III (Contaminated) IV (Checking)
0.353 0.350 0.540
– 0.460 0.314
– – 0.457
Table 3 Intercorrelations between the total score of the PI and its subscales Scale
PI total
Impaired control
Impulsive
Contaminated
Impaired control Impulsive Contaminated Checking
0.865 0.716 0.752 0.769
– 0.472 0.491 0.652
– – 0.472 0.379
– – – 0.490
All correlation coefficients are p < 0.01. Table 4 Correlations between the PI and two OCPD measures Scales
PI total
Impaired
Impulsive
Contaminated
Checking
OCPD screening 20 PDQ-4:OCPD items
0.574 0.475
0.546 0.474
0.282 0.209
0.340 0.281
0.498 0.420
All correlation coefficients are p < 0.01.
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with two OCPD measures, while ‘Impulsive thoughts’ and ‘Being contaminated’ did not correlate well with the two OCPD measures. The correlation between two OCPD measures was r = 0.79. In order to examine the relationship between characteristics of OCD and OCPD in the non-clinical population, we applied regression analyses to our data. A standard multiple regression analysis was performed with the score of 20-item OCPD screening questions as the predicted variable and four subscales from the PI-J as predictor variables. The PI-J scales predicted 32.9% of the variability in the score of 20-item OCPD screening questions. Similarly, standard multiple regression analysis performed on the PDQ-4 showed relatively small R2 values (23.6%).
4. Discussion The present study examined the psychometric properties and factor structure of the Padua Inventory, and whether scores on the PI reflecting obsessive–compulsiveness can be discriminated from the degree of obsessive–compulsive personality traits, in Japanese student samples. The psychometric properties of the PI-J were satisfactory in general. The total score showed relatively normal distribution, and it suggested the PI could measure individual differences in the degree of obsessive–compulsive traits in normal population. There was no evidence for sex differences in the Japanese sample, which is consistent with the results in most of the previous studies (Goodarzi & Firoozabadi, 2005; MacDonald & de Silva, 1999; Sternberger & Burns, 1990; Van Oppen, 1992), except the findings of Sanavio (1988), who reported females scored significantly higher than males on the total PI score. This suggests sex difference do not exist in the degree of obsessive–compulsive traits in the non-clinical population. The PI-J and its four subscales showed good internal consistencies with Cronbach’s alpha, showing 0.95 in the full scale and ranging from 0.84 to 0.88 in subscales. These results suggest that the PI-J is a reliable instrument to measure individual differences in the degree of obsessive– compulsive traits in Japan. The results of the explanatory factor analysis revealed a four-factor structure similar to those found using the PI in previous Italian and American studies (Sanavio, 1988; Sternberger & Burns, 1990). Those factors explained 36% of the variance in the present investigation, though this percentage of variance could be regarded as not enough to be acceptable. However, it is very close to the variance reported by the American study (38%). Although there was some difference between the result in this study and those in the other countries for the items, which loaded on each factor, ‘Being contaminated’ was almost identical between the three countries. The findings for the ‘Impaired control’ factor obtained in this study corresponded relatively well with the same factor in the Italian and American studies, although not as closely as the ‘Being contaminated’ factor. Regarding these two factors, it appeared that they were core and universal constructs of OCD. However, factor II (‘Impulsive thoughts’) found in this study contained three other items in which two were found in the ‘Impaired control’ factor in the Italian and American studies, although this factor contained most of the items in corresponding factors in the Italian and American studies. On the other hand, factor IV (Checking behaviours) found in this study did not contain two in Sanavio’s and five in Sternberger and Burns’ items in their corresponding factors. These results suggest some of the constructs in OCD might differ between the countries.
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The findings showed that the PI’s four-factor structure is rather stable across different cultures as a whole, and a result of CFA also suggested that this four-factor model derived from the Japanese sample met acceptable criteria, although their results suggested that there is room for improving the model. However, they also suggest some differences among countries in the obsessions and compulsions involved in OCD. Such differences might be explained partly by cultural variation in social behaviour. These variations are especially pronounced in non-clinical populations, since their thoughts and behaviours are largely regulated by the social standards in which they live. Further studies can investigate which socio-cultural factors may account for these differences in obsessive–compulsive characteristics found in various countries. The total score of the PI in the Japanese sample was higher than in western countries (for example, Sanavio, 1988; Sternberger & Burns, 1990) and other non-western countries (for example, Goodarzi & Firoozabadi, 2005) studied. Although it is possible that item translation may have affected scores to some extent, we feel the difference of 20–30 points could not be explained by a translation effect alone. Instead, the results suggest that some obsessive–compulsive traits are more common in Japanese people compared to the people in other countries. For example, some tendencies of meticulous, punctualness, and cleanliness are widely seen in most Japanese behaviours. These tendencies are certainly related to some core traits in OCD. The high score of the PI in the Japanese sample is probably due to those socio-cultural characteristics to a large extent. Although there is no epidemiological research, which found higher rates of OCD in Japan compared to the other countries, this is not surprising. In assessing an individual for OCD, the clinician does not include culturally prescribed thoughts and behaviours that reflect habits, customs or interpersonal styles, based on the DSM-IV-TR (APA, 2000). Thus, the number of diagnoses for OCD in Japan is not higher than the other countries, whereas most non-clinical Japanese people have a tendency to recognize obsessive–compulsive like characteristics in themselves to some extent. Regarding the relationship between the PI and the OCPD measures, the total score of the PI moderately correlated with two OCPD measures. However, the subscales of ‘Impaired control’ and ‘Checking behaviour’ showed only moderate correlations with two OCPD measures, and the subscales of ‘Impulsive thoughts’ and ‘Being contamination’ failed to show substantial correlations with OCPD measures. These results in non-clinical samples mirror the similarities and differences in diagnostic standards of OCD and OCPD. That is, OCD and OCPD have similarities in doubtfulness (suspicious) and checking behaviours, while most people with OCPD do not show the obsessions of contamination or impulsive thoughts that are commonly seen in OCD. The results of multiple regression analyses also showed the PI did not adequately explain the scores in two OCPD measures. These findings suggest it is possible to discriminate between the degree of OCD and OCPD traits in the normal population, and that PI measures OCD better than OCPD.
5. Conclusion As a whole, the results in this study showed evidence of good reliability and validity of the PI in a non-clinical Japanese sample. The PI-J appears to be a practical instrument for assessing obsessive–compulsive tendency in the normal population in Japan.
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However, the results of the present study partly differed from previous results carried out in other countries. This suggests that there are cultural differences in the Japanese sample for the expression of obsessions and compulsions, mainly in the factors of ‘Impulsive thoughts’ and ‘Checking behaviours’. Some questions still remain, such as that the data reported in this paper is exclusively from University students. It is possible that different results may emerge if subjects are not students. Additionally, it would be necessary to administer the PI to clinical samples who were diagnosed as being OCD in order to examine the diagnostic validity of the PI in Japan, although the convergent validity of the PI with the MOCI was confirmed in an earlier study (Sugiura & Tanno, 2000). Further researches are needed to clarify these problems. Acknowledgement We thank Chris Ashwin for valuable comments on our earlier draft of this manuscript. References American Psychiatric Association (2000). Diagnostic and statistical manual of mental disorders (4th ed., Text Revised). Washington, DC: American Psychiatric Association. Antony, M. M., Downie, F., & Swinson, R. P. (1998). Diagnostic issue and epidemiology in obsessive–compulsive disorder. In R. P. Swinson, M. M. Antony, S. Rachman, & M. A. Richter (Eds.), Obsessive–compulsive disorder: Theory, research, and treatment (pp. 3–32). New York: Guilford. Arbuckle, J. L. (2005). Amos 6.01. Chicago: Smallwaters Corp. Burns, G. L., Formea, G. M., Keortge, S. G., & Sternberger, L. G. (1995). The utilization of nonpatient samples in the study of obsessive compulsive disorder. Behaviour Research and Therapy, 33, 133–144. Goodarzi, M. A., & Firoozabadi, A. (2005). Reliability and validity of the Padua Inventory in an Iranian population. Behaviour Research and Therapy, 43, 43–54. Hodgson, R. J., & Rachman, S. (1977). Obsessional-compulsive complaints. Behaviour Research and Therapy, 15, 389–395. Hollander, E., & Wong, C. M. (1995). Obsessive–compulsive spectrum disorders. Journal of Clinical Psychiatry, 56(Suppl. 4), 3–6. Hyler, S. E. (2004). Personality diagnostic questionnaire (PDQ) version 4. New York: Human Information Inc. Kasahara, Y. (1976). On the preborbid personality of depression. In Y. Kasahara (Ed.). Psychopathology of manicdepressive disorder (Vol. 1, pp. 1–29). Tokyo: Kobundo Press (in Japanese). Kyrios, M., Bhar, S., & Wade, D. (1996). The assessment of obsessive–compulsive phenomena: Psychometric and normative data on the Padua Inventory from as Australian non-clinical student sample. Behaviour Research and Therapy, 34, 85–95. MacDonald, A. M., & de Silva, P. (1999). The assessment of obsessionality using the Padua Inventory: Its validity in a British non-clinical sample. Personality and Individual Differences, 27, 1027–1048. McCullough, P. K., & Maltsberger, J. T. (1996). Obsessive–compulsive personality disorder. In G. O. Gabbard & S. D. Atkinson (Eds.), Synopsis of treatments of psychiatric disorders (2nd ed., pp. 2367–2376). Washington DC: American Psychiatric Press. Pollak, J. M. (1995). Commentary on obsessive–compulsive personality disorder. In W. J. Livesley (Ed.), The DSM-IV personality disorders (pp. 282–283). New York: The Guilford Press. Rachman, S., & de Silva, P. (1978). Abnormal and normal obsessions. Behaviour Research and Therapy, 16, 233–248. Salkovskis, P. M., & Harrison, J. (1984). Abnormal and normal obsessions – A replication. Behaviour Research and Therapy, 22, 544–552.
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Sanavio, E. (1988). Obsessions and compulsions: The Padua Inventory. Behaviour Research and Therapy, 26, 169–177. Sternberger, L. G., & Burns, G. L. (1990). Obsessions and compulsions: Psychometric properties of the Padua Inventory with an American college population. Behaviour Research and Therapy, 28, 341–345. Sugiura, Y., & Tanno, Y. (2000). Self-report inventory of obsessive–compulsive symptoms: Reliability and validity of the Japanese version of the Padua Inventory. Psychiatric Diagnostics Quarterly, 11, 175–189 (in Japanese). Van Oppen, P. (1992). Obsessions and compulsions: Dimensional structure, reliability, convergent and divergent validity of the Padua Inventory. Behaviour Research and Therapy, 30, 631–637. Van Oppen, P., Hoekstra, R. J., & Emmelkamp, P. M. G. (1995). The structure of obsessive–compulsive symptoms. Behaviour Research and Therapy, 33, 15–23. Wells, A., & Morrison, A. P. (1994). Qualitative dimensions of normal worry and normal obsession: A comparative study. Behaviour Research and Therapy, 32, 867–870. World Health Organization (1992). The international classification of diseases (10th revision). Geneva: World Health Organization. Zimmerman, M. (1994). Interview guide for evaluating DSM-IV psychiatric disorders and the mental states examination. East Greenwich, RI: Psych Products Press.
Psychometric properties of the Padua Inventory in a sample of Japanese university students Akio Wakabayashi
a,b,*
, Tadashi Aobayashi
a
a b
Department of Psychology, Chiba University, 1-33 Yayoi-cho, Inage, Chiba 263-8522, Japan Autism Research Centre, Department of Psychiatry, University of Cambridge, Douglas House, 18b Trumpington Road, Cambridge CB2 2AH, UK Received 6 April 2006; received in revised form 1 March 2007; accepted 6 March 2007 Available online 30 April 2007
Abstract The psychometric properties and factor structure of the Padua Inventory (PI), a measure of obsessive– compulsive phenomena, were examined in a non-clinical sample of 671 Japanese university students. Results showed high internal consistencies of both the total scale and its subscales in the Japanese sample. A factor analysis replicated a four-factor structure, consisting of three factors corresponding to those found in previous studies (‘Impaired control of mental activity’, ‘Being contaminated’ and ‘Checking behaviour’) and one factor (‘Impulsive thoughts’), which partly differed from that found previously. The total score of the PI correlated moderately with two Obsessive–Compulsive Personality Disorder (OCPD) measures, but two subscales of the PI did not show a correlation with OCPD. Results of a multiple regression analysis revealed the PI did not explain the degree of OCPD traits well, suggesting the PI measures OCD traits better than OCPD in non-clinical samples. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Obsessive–Compulsive Disorder (OCD); Obsessive–Compulsive Personality Disorder (OCPD); Padua Inventory; Non-clinical group; Factor structure
*
Corresponding author. Address: Department of Psychology, Chiba University, 1-33 Yayoi-cho, Inage, Chiba 2638522, Japan. E-mail address: [email protected] (A. Wakabayashi). 0191-8869/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.paid.2007.03.004
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1. Introduction The central features of obsessive–compulsive disorder (OCD) are unwanted and intrusive thoughts, impulses, or images that cause striking distress or anxiety accompanied by compulsive or ritual behaviours (DSM-IV-TR; APA, 2000). While the prevalence rate of OCD is about 2– 3% of the general population (Antony, Downie, & Swinson, 1998), research has shown that obsessions are actually normally occurring phenomena in non-clinical people (Rachman & de Silva, 1978; Salkovskis & Harrison, 1984; Wells & Morrison, 1994). These findings suggest OCD characteristics are more common than previously believed, and have led to several analogue (continuum hypothesis) studies of OCD in recent decades (for example, Burns, Formea, Keortge, & Sternberger, 1995). Although several measurement tools exist for OCD, the Padua Inventory (PI) (Sanavio, 1988) is one of the most frequently used instruments to measure obsessive–compulsive tendency in both clinical and non-clinical samples. The PI is a self-report inventory that assesses the degree of disturbance or difficulty that 60 different thoughts and behaviours engender for the individual. Sanavio (1988) reported results of a study in the Italian population showing the PI has very good reliability and validity. Sternberger and Burns (1990) replicated the psychometric properties of the PI in American college-students samples, and confirmed almost identical psychometric properties and factor structures of the PI. Further support for the reliability and validity of the PI has emerged from studies in other countries (for example, Kyrios, Bhar, & Wade, 1996; MacDonald & de Silva, 1999; Van Oppen, Hoekstra, & Emmelkamp, 1995), including a pilot study of the PI in Japan which reported its factor structure and convergent validity with the Maudsley ObsessionalCompulsive Inventory (MOCI; Hodgson & Rachman, 1977; Sugiura & Tanno, 2000), although its sample size was not enough. These findings show the validity and factor structure of the PI is consistent across samples from different countries. The four-factor structure of the PI, by PCA with Varimax rotation method, has been commonly shown throughout several countries, although some differences exist in the content of these factors. This suggests that obsessions and compulsions, which represent the core symptoms in OCD, might differ between countries to some extent. For example, the items loading on Factor I, which were believed to be core characteristics of OCD, obtained in Italian samples found only two-thirds of the items in the corresponding factor extracted from an American samples. Although the diagnostic standard of OCD should be universally common, because it is based on international standards (DSM-IV-TR, 2000 and ICD-10, 1992), the pattern of obsessions and compulsions seen in non-clinical people likely differs between countries to some extent. This is because the thoughts and behaviours of people in various cultures are affected by different social norms and habits, which are characteristic to each country. For example, clinical characteristics such as ‘clean and tidy’ and ‘incompleteness and checking’, which are parts of core components in OCD, are more commonly seen in Japanese people in everyday life compared to other countries (Kasahara, 1976). This is because these behavioural tendencies are closely connected to the social norms and habits particular to the Japanese society. Therefore, some ‘traits’ involving obsessive– compulsive behaviours are found widely in the normal population, and it might cause the elevation of the PI score in a non-clinical sample in Japan. Like obsessive–compulsive traits, obsessive–compulsive personality traits are also disseminated widely in the normal population (Pollak, 1995). This suggests the obsessive–compulsive personality style is also understood as falling along a continuum of severity from an adaptive coping style
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to an exaggerated and maladaptive expression (Hollander & Wong, 1995). However, unlike other personality disorders that are seen as part of a spectrum disorder, from a clinical view OCPD is not currently seen in the same spectrum of OCD. From this perspective, OCPD and OCD are defined as separate and distinct disorders (McCullough & Maltsberger, 1996). In line with this idea, the majority of individuals with OCD do not meet the criteria for OCPD (APA, 2000). According to DSM-IV-TR the essential features of OCPD are a preoccupation with orderliness, perfectionism, and control at the expense of flexibility, openness, and efficiency. Individuals with OCPD force themselves and others to follow rigid moral principles and very high standards of performance, and are inclined to be severely self-critical. These individuals are also deferential to authority and rules, and insist on literal compliance, regardless of circumstances (APA, 2000).1 Although OCD and OCPD are diagnostically differentiated, there are common features between them. For example they both show certain similarities in checking behaviours and in doubtfulness (suspicious). On the other hand, most people with OCPD do not show obsessions of contamination or impulsive thoughts, which are commonly seen in OCD. Consequently, since OCD and OCPD are discriminated from one another at the clinical level, an interesting question emerges about how well the thoughts and behaviours of these constructs are differentiated in the normal population. This leads to a question of whether the PI best measures obsessive–compulsive traits found in OCD or those seen in OCPD. If the results obtained from the PI are not highly correlated to OCPD measures, this would suggest that PI measures reflect obsessive–compulsive traits in OCD in the normal population. From this we would hypothesise the existence of a spectrum for obsessive and compulsive behaviours, ranging from those seen in the normal population to extreme expressions in OCD. However, if the PI scores show better correlations with OCPD measures, it would suggest the PI has limited ability to discriminate the degree of the traits found in OCD from those in OCPD. The aim in this study is to examine the psychometric properties and factor structure of the PI in a large non-clinical Japanese sample. Additionally, we aim to investigate the relationship between the characteristics of OCD measured by the PI and those in OCPD measures seen in a non-clinical population. 2. Method 2.1. Participants The participants were 671 (381 males and 290 females) undergraduate students in various majors/courses in Chiba University. Their mean age was 19.1 (SD = 1.17: range 17–28 yr). 2.2. Measures The Padua Inventory Japanese version (PI-J): The PI (Sanavio, 1988) is a 60-item self-report inventory, which measures obsessions and compulsions. The PI is considered to measure the 1
The ICD-10 (WHO, 1992) has a category called Anankastic Personality Disorder (APD), which corresponds to the description of OCPD in DSM-IV-TR (APA, 2000). APD is characterized by doubt, perfectionism, conscientiousness, checking and preoccupation with details, stubbornness, caution and rigidity.
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extent to which the obsessions and compulsions interfere with routine daily functioning. Each item, rated on a 5-point scale, measures the degree of disturbance caused by the thought or behaviour (0 = ‘not at all’ to 4 = ‘very much’). The total score is the sum of the 60 items. We used the Japanese version of the PI (Sugiura & Tanno, 2000), that was translated as accurately as possible from original descriptions under supervision by psychiatric specialists, with a back translation process. The OCPD screening 20: This 20-item inventory was developed to measure the degree of obsessive–compulsive personality traits based on the screening questions proposed by Zimmerman (1994) in the assessment of individuals with OCPD. This was converted to a 5-point rating scale, so that it could be directly compared to the PI. The PDQ-4:OCPD: The 8 items of the obsessive–compulsive personality disorders from the Personality Diagnostic Questionnaire 4th edition (PDQ-4; Hyler, 2004): The PDQ-4 is a 100-item, self-administered, true/false questionnaire that yields personality diagnoses consistent with the DSM-IV diagnostic criteria for the axis II disorders. We also modified this to a 5-point rating scale. 2.3. Procedure The PI-Japanese version (PI-J) was administered in groups during the classes of introductory psychology. The items of the PI-J were randomized in order to avoid continuing similar descriptions. Two hundreds and thirty two (134 males and 98 females) of the participants, who were randomly extracted, were asked to respond to two OCPD measures about two months after they took the PI-J.
3. Results 3.1. Fundamental psychometric properties of the PI-J All the questionnaires that had items with no response and had the same responses in all items were rejected. The mean total score of the PI-J was 72.7 (SD = 34.76) with a range of 2–179. The kurtosis was 0.42, and the skewness was 0.18. There was no significant difference between females (M = 72.7, SD = 35.15) and males (M = 72.6, SD = 34.24) (t(669) = 0.044, p = 0.965; two tailed). Cronbach’s alpha coefficient was calculated as an index of consistency in all items and to be 0.95. 3.2. Factor structure First, in order to compare with the earlier studies (Sanavio, 1988; Sternberger & Burns, 1990), a principal components analysis with Varimax rotation method was used to investigate the factor structure of the PI. Five factors had eigenvalues above 1.0. A plot of the eigenvalues (Kaiser criterion) and the pattern of factor loadings (Cattell’s scree) suggested a four-factor solution would be best. These four factors explained 36.1% of the variance. Then we also administered factor analysis by oblique rotation (Promax method), because it appeared the factors obtained might
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correlate highly with each other as components of obsessive–compulsive tendencies. The result of oblique rotation showed almost identical factor structure to the result of Varimax rotation. The items, which loaded on each factor with loadings 0.40 and over were identical in two factor structures. Table 1 shows the items loaded on the four factors. The inter-factors correlations in the oblique solution are shown in Table 2. Factor I, which corresponded to ‘Impaired control of mental activities’ named by Sanavio (1988), contained 14 items. Most items, which loaded on this factor, replicated the items which loaded on the corresponding factor in the studies by Sanavio (1988) and Sternberger and Burns (1990). Factor II (‘Urges and worries of losing control of motor behaviour’) contained 12 items. This factor contained 9 items, which loaded on the corresponding factors in Sternberger and Burns (1990), but only 6 of 12 items consistent with the corresponding factor in Sanavio (1988). Factor III (‘Being contaminated’), contained 13 items. The items, which loaded on this factor, replicated the items which load on the corresponding factor in the earlier studies (Sanavio, 1988; Sternberger & Burns, 1990). Factor IV (‘Checking behaviours’) contained 6 items. These items loaded on the corresponding factors in Sanavio (1988) and Sternberger and Burns (1990). Additionally, Confirmatory Factor Analysis (CFA) was performed on the 45 items employing the Amos 6.01 (Arbuckle, 2005). The estimation method was Maximum Likelihood. Each of 45 items was linked to each correspondent factor based on the result of the EFA. The result of a CFI yielded a v2939 ¼ 3225:41, with a CFI = 0.86, GFI = 0.90, and a RMSEA = 0.06. 3.3. Subscale scores and their reliabilities Subscale scores were calculated according to the results of the two factor analyses. The average scores of the subscales were as follows. The subscale-1 (‘Impaired control of mental activities’ or ‘Doubt for own acts which have been done’, which consisted of 14 items) was 25.9 (SD = 11.40), and Cronbach’s alpha was 0.88. The subscale-2 (‘Impulsive thoughts’, which consisted of 12 items) was 7.7 (SD = 7.38), and Cronbach’s alpha was 0.84. The subscale-3 (‘Being contaminated’, which consisted of 13 items) was 11.4 (SD = 8.75), and Cronbach’s alpha was 0.87. The subscale-4 (‘Checking behaviours’, which consisted of 6 items) was 9.6 (SD = 5.80), and Cronbach’s alpha was 0.84. There were no sex differences for the subscale scores (all ts < 1.00), except ‘‘Impulsive thoughts’’ in which males scored higher than females (t(669) = 2.497, p < 0.05). The intercorrelation among the subscale scores and correlations between four subscale scores and total score of the PI-J are shown in Table 3. 3.4. The relation and differences between the PI and two OCPD measures Psychometric properties of two OCPD measures used in this study were calculated. In the 20item OCPD screening questions, the mean score was 17.2 (SD = 11.98), and its Cronbach’s alpha was 0.83. In the 8-item OCPD scale in the PDQ-4, its mean score was 7.4 (SD = 5.33). Its Cronbach’s alpha was 0.68. There was no sex difference found for the mean scores in either scale (ts(230) = 0.215 and 0.213, n.s., respectively). The correlations between the Padua Inventory and two OCPD measures were shown in Table 4. The total score of the PI-J correlated moderately with two OCPD measures. In the subscales of the PI-J, ‘Impaired control of mental activity’ and ‘Checking behaviour’ correlated moderately
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Table 1 Factors and factor loadings for the Padua items Item Factor I: Impaired control of mental activities (Doubts about control of mental activities) 29. After doing something carefully, I still have the impression I have either done it badly or not finished it 33. Unpleasant thoughts come into my mind against my will and I cannot get rid of them 36. I imagine catastrophic consequences as a result of absent-mindedness or minor errors which I make 37. I think or worry at length about having hurt someone without knowing it 32. When I start thinking of certain things I become obsessed with them 45. In certain situations, I am afraid of losing my self-control and doing embarrassing things 26. I find it difficult to make decisions, even about unimportant matters 18. I have to do things several times before I think they are properly done 28. I have the impression that I will never be able to explain things clearly, especially when talking about important matters that involve me 11. When doubt and worries come to my mind, I cannot rest until I have talked them over with a reassuring person 44. When a thought or doubt comes into my mind, I have to examine it from all points of view and cannot stop until I have done so 12. When I talk, I tend to repeat the same things and the same sentence several times 13. I tend to ask people to repeat the same things to me several times consecutively even though I did understand what they said the first time 43. I worry about remembering completely unimportant things and make an effort not to forget them Factor II: Impulsive thoughts (Urges and worries of losing control of motor behaviour) 55. I am sometimes almost irresistibly tempted to steal something from the supermarket 48. At certain moments I am tempted to tear off my clothes in public 54. I sometimes have an impulse to steal other people’s belongings even if they are of no use to me 56. I sometimes have an impulse to hurt defenseless children or animals 46. When I look down from a bridge or a very high window, I feel an impulse to throw myself into space 49. While driving, I sometimes feel an impulse to drive the car into someone or something 35. My brain constantly goes its own way and I find it difficult to attend to what is happening around me 59. When I hear about a suicide or crime, I am upset for a long time and find it difficult to stop thinking about it 51. I get upset and worried at the sight of knives, daggers and other pointed objects 47. When I see a train approaching I sometimes think I could throw myself under its wheels 53. I sometimes feel the need to break or damage things for no reason 50. Seeing weapons excites me and makes me think violent thoughts Factor III: Being contaminated 8. I sometimes have to wash or clean myself simply because I think I may be dirty or contaminated 9. If I touch something I think is ‘contaminated’, I immediately have to wash or clean myself 7. I wash my hands more often and longer than necessary 60. I invent useless worries about germs and disease 5. I avoid using public toilets because I am afraid of disease and contamination
Loadings 0.638 (0.613) 0.616 (0.637) 0.583 (0.522) 0.580 0.572 0.565 0.526 0.517 0.488
(0.572) (0.609) (0.571) (0.473) (0.486) (0.505)
0.471 (0.511) 0.467 (0.428) 0.464 (0.463) 0.462 (0.446) 0.450 (0.427)
0.685 (0.701) 0.641 (0.667) 0.632 (0.647) 0.578 (0.622) 0.547 (0.583) 0.540 (0.539) 0.538 (0.509) 0.508 (0.488) 0.501 0.478 0.446 0.438
(0.479) (0.521) (0.452) (0.442)
0.633 (0.615) 0.585 0.580 0.573 0.567
(0.564) (0.547) (0.556) (0.543)
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Table 1 (continued) Item
Loadings
10. If an animal touches me, I feel dirty and immediately have to wash myself or change my clothing 14. I feel obliged to follow a particular order in dressing, undressing and washing myself 6. I avoid public telephones because I am afraid of contagion or disease 10. Before going to bed I have to hang up or fold my clothes in a special way 1. I feel my hands are dirty when I touch money 2. I think even slight contact with bodily secretions (perspiration, saliva, urine, etc.) may contaminate my clothes or somehow harm me 3. I find it difficult to touch an object when I know it has been touched by strangers or by certain people 15. Before going to sleep I have to do certain things in a certain order
0.537 (0.572) 0.535 0.509 0.508 0.500 0.447
(0.557) (0.501) (0.483) (0.570) (0.487)
0.437 (0.433) 0.427 (0.439)
Factor IV: Checking behaviours 20. I check and recheck gas and water taps and light switches after turning them off 22. I keep on checking forms, documents, checks, etc. in detail to make sure I have filled them in correctly 21. I return home to check doors, windows, drawers, etc. to make sure they are properly shut 23. I keep on going back to see that matches, cigarettes, etc. are properly extinguished 25. I check letters carefully many times before posting them 27. Sometimes, I am not sure I have done things which in fact I know I have done
0.659 (0.731) 0.654 (0.694) 0.620 0.573 0.496 0.483
(0.679) (0.603) (0.499) (0.473)
Note: Only loading >0.40 are shown by ‘Varimax’ (Promax) rotated solutions.
Table 2 Intercorrelations between four factors obtained in oblique solution Factors
I (Impaired control)
II (Impulsive)
III (Contaminated)
II (Impulsive) III (Contaminated) IV (Checking)
0.353 0.350 0.540
– 0.460 0.314
– – 0.457
Table 3 Intercorrelations between the total score of the PI and its subscales Scale
PI total
Impaired control
Impulsive
Contaminated
Impaired control Impulsive Contaminated Checking
0.865 0.716 0.752 0.769
– 0.472 0.491 0.652
– – 0.472 0.379
– – – 0.490
All correlation coefficients are p < 0.01. Table 4 Correlations between the PI and two OCPD measures Scales
PI total
Impaired
Impulsive
Contaminated
Checking
OCPD screening 20 PDQ-4:OCPD items
0.574 0.475
0.546 0.474
0.282 0.209
0.340 0.281
0.498 0.420
All correlation coefficients are p < 0.01.
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with two OCPD measures, while ‘Impulsive thoughts’ and ‘Being contaminated’ did not correlate well with the two OCPD measures. The correlation between two OCPD measures was r = 0.79. In order to examine the relationship between characteristics of OCD and OCPD in the non-clinical population, we applied regression analyses to our data. A standard multiple regression analysis was performed with the score of 20-item OCPD screening questions as the predicted variable and four subscales from the PI-J as predictor variables. The PI-J scales predicted 32.9% of the variability in the score of 20-item OCPD screening questions. Similarly, standard multiple regression analysis performed on the PDQ-4 showed relatively small R2 values (23.6%).
4. Discussion The present study examined the psychometric properties and factor structure of the Padua Inventory, and whether scores on the PI reflecting obsessive–compulsiveness can be discriminated from the degree of obsessive–compulsive personality traits, in Japanese student samples. The psychometric properties of the PI-J were satisfactory in general. The total score showed relatively normal distribution, and it suggested the PI could measure individual differences in the degree of obsessive–compulsive traits in normal population. There was no evidence for sex differences in the Japanese sample, which is consistent with the results in most of the previous studies (Goodarzi & Firoozabadi, 2005; MacDonald & de Silva, 1999; Sternberger & Burns, 1990; Van Oppen, 1992), except the findings of Sanavio (1988), who reported females scored significantly higher than males on the total PI score. This suggests sex difference do not exist in the degree of obsessive–compulsive traits in the non-clinical population. The PI-J and its four subscales showed good internal consistencies with Cronbach’s alpha, showing 0.95 in the full scale and ranging from 0.84 to 0.88 in subscales. These results suggest that the PI-J is a reliable instrument to measure individual differences in the degree of obsessive– compulsive traits in Japan. The results of the explanatory factor analysis revealed a four-factor structure similar to those found using the PI in previous Italian and American studies (Sanavio, 1988; Sternberger & Burns, 1990). Those factors explained 36% of the variance in the present investigation, though this percentage of variance could be regarded as not enough to be acceptable. However, it is very close to the variance reported by the American study (38%). Although there was some difference between the result in this study and those in the other countries for the items, which loaded on each factor, ‘Being contaminated’ was almost identical between the three countries. The findings for the ‘Impaired control’ factor obtained in this study corresponded relatively well with the same factor in the Italian and American studies, although not as closely as the ‘Being contaminated’ factor. Regarding these two factors, it appeared that they were core and universal constructs of OCD. However, factor II (‘Impulsive thoughts’) found in this study contained three other items in which two were found in the ‘Impaired control’ factor in the Italian and American studies, although this factor contained most of the items in corresponding factors in the Italian and American studies. On the other hand, factor IV (Checking behaviours) found in this study did not contain two in Sanavio’s and five in Sternberger and Burns’ items in their corresponding factors. These results suggest some of the constructs in OCD might differ between the countries.
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The findings showed that the PI’s four-factor structure is rather stable across different cultures as a whole, and a result of CFA also suggested that this four-factor model derived from the Japanese sample met acceptable criteria, although their results suggested that there is room for improving the model. However, they also suggest some differences among countries in the obsessions and compulsions involved in OCD. Such differences might be explained partly by cultural variation in social behaviour. These variations are especially pronounced in non-clinical populations, since their thoughts and behaviours are largely regulated by the social standards in which they live. Further studies can investigate which socio-cultural factors may account for these differences in obsessive–compulsive characteristics found in various countries. The total score of the PI in the Japanese sample was higher than in western countries (for example, Sanavio, 1988; Sternberger & Burns, 1990) and other non-western countries (for example, Goodarzi & Firoozabadi, 2005) studied. Although it is possible that item translation may have affected scores to some extent, we feel the difference of 20–30 points could not be explained by a translation effect alone. Instead, the results suggest that some obsessive–compulsive traits are more common in Japanese people compared to the people in other countries. For example, some tendencies of meticulous, punctualness, and cleanliness are widely seen in most Japanese behaviours. These tendencies are certainly related to some core traits in OCD. The high score of the PI in the Japanese sample is probably due to those socio-cultural characteristics to a large extent. Although there is no epidemiological research, which found higher rates of OCD in Japan compared to the other countries, this is not surprising. In assessing an individual for OCD, the clinician does not include culturally prescribed thoughts and behaviours that reflect habits, customs or interpersonal styles, based on the DSM-IV-TR (APA, 2000). Thus, the number of diagnoses for OCD in Japan is not higher than the other countries, whereas most non-clinical Japanese people have a tendency to recognize obsessive–compulsive like characteristics in themselves to some extent. Regarding the relationship between the PI and the OCPD measures, the total score of the PI moderately correlated with two OCPD measures. However, the subscales of ‘Impaired control’ and ‘Checking behaviour’ showed only moderate correlations with two OCPD measures, and the subscales of ‘Impulsive thoughts’ and ‘Being contamination’ failed to show substantial correlations with OCPD measures. These results in non-clinical samples mirror the similarities and differences in diagnostic standards of OCD and OCPD. That is, OCD and OCPD have similarities in doubtfulness (suspicious) and checking behaviours, while most people with OCPD do not show the obsessions of contamination or impulsive thoughts that are commonly seen in OCD. The results of multiple regression analyses also showed the PI did not adequately explain the scores in two OCPD measures. These findings suggest it is possible to discriminate between the degree of OCD and OCPD traits in the normal population, and that PI measures OCD better than OCPD.
5. Conclusion As a whole, the results in this study showed evidence of good reliability and validity of the PI in a non-clinical Japanese sample. The PI-J appears to be a practical instrument for assessing obsessive–compulsive tendency in the normal population in Japan.
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However, the results of the present study partly differed from previous results carried out in other countries. This suggests that there are cultural differences in the Japanese sample for the expression of obsessions and compulsions, mainly in the factors of ‘Impulsive thoughts’ and ‘Checking behaviours’. Some questions still remain, such as that the data reported in this paper is exclusively from University students. It is possible that different results may emerge if subjects are not students. Additionally, it would be necessary to administer the PI to clinical samples who were diagnosed as being OCD in order to examine the diagnostic validity of the PI in Japan, although the convergent validity of the PI with the MOCI was confirmed in an earlier study (Sugiura & Tanno, 2000). Further researches are needed to clarify these problems. Acknowledgement We thank Chris Ashwin for valuable comments on our earlier draft of this manuscript. References American Psychiatric Association (2000). Diagnostic and statistical manual of mental disorders (4th ed., Text Revised). Washington, DC: American Psychiatric Association. Antony, M. M., Downie, F., & Swinson, R. P. (1998). Diagnostic issue and epidemiology in obsessive–compulsive disorder. In R. P. Swinson, M. M. Antony, S. Rachman, & M. A. Richter (Eds.), Obsessive–compulsive disorder: Theory, research, and treatment (pp. 3–32). New York: Guilford. Arbuckle, J. L. (2005). Amos 6.01. Chicago: Smallwaters Corp. Burns, G. L., Formea, G. M., Keortge, S. G., & Sternberger, L. G. (1995). The utilization of nonpatient samples in the study of obsessive compulsive disorder. Behaviour Research and Therapy, 33, 133–144. Goodarzi, M. A., & Firoozabadi, A. (2005). Reliability and validity of the Padua Inventory in an Iranian population. Behaviour Research and Therapy, 43, 43–54. Hodgson, R. J., & Rachman, S. (1977). Obsessional-compulsive complaints. Behaviour Research and Therapy, 15, 389–395. Hollander, E., & Wong, C. M. (1995). Obsessive–compulsive spectrum disorders. Journal of Clinical Psychiatry, 56(Suppl. 4), 3–6. Hyler, S. E. (2004). Personality diagnostic questionnaire (PDQ) version 4. New York: Human Information Inc. Kasahara, Y. (1976). On the preborbid personality of depression. In Y. Kasahara (Ed.). Psychopathology of manicdepressive disorder (Vol. 1, pp. 1–29). Tokyo: Kobundo Press (in Japanese). Kyrios, M., Bhar, S., & Wade, D. (1996). The assessment of obsessive–compulsive phenomena: Psychometric and normative data on the Padua Inventory from as Australian non-clinical student sample. Behaviour Research and Therapy, 34, 85–95. MacDonald, A. M., & de Silva, P. (1999). The assessment of obsessionality using the Padua Inventory: Its validity in a British non-clinical sample. Personality and Individual Differences, 27, 1027–1048. McCullough, P. K., & Maltsberger, J. T. (1996). Obsessive–compulsive personality disorder. In G. O. Gabbard & S. D. Atkinson (Eds.), Synopsis of treatments of psychiatric disorders (2nd ed., pp. 2367–2376). Washington DC: American Psychiatric Press. Pollak, J. M. (1995). Commentary on obsessive–compulsive personality disorder. In W. J. Livesley (Ed.), The DSM-IV personality disorders (pp. 282–283). New York: The Guilford Press. Rachman, S., & de Silva, P. (1978). Abnormal and normal obsessions. Behaviour Research and Therapy, 16, 233–248. Salkovskis, P. M., & Harrison, J. (1984). Abnormal and normal obsessions – A replication. Behaviour Research and Therapy, 22, 544–552.
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