A Japanese version of the Perceived Stress Scale: cross-cultural translation and equivalence assessment

This paper reports the translation of the Perceived Stress Scale (PSS) [1] from English to Japanese and equivalence assessment between the original PSS and the translated version (PSS-J) for use in a cross-cultural study of occupational stress amongst trainee health professionals.

There are many approaches to measuring stress and in any given study it is important to consider conceptual, practical and scientific aspects [2]. Many theorists have provided three broad categorisations of stress (e.g., [3–6]). A strong commonality among these categorisations is that the first concept puts the emphasis on stressful events, the second on consequences of stress and the third on individual appraisals of situations. However, there is a growing consensus that stress arises from an imbalance between the individual's perception of demand charged by the situation and his/her estimate of the ability to cope with the demand [4]. That is to say the experience of stress is dependent upon the individual appraisal of external stressor and his/her own capability. In the context of a cross-cultural study, conceptualising stress by focusing on specific stressful events and/or particular responses runs the risk of being inherently culture bound in measuring stress because it requires a common perception of that which is potentially stressful, a common opportunity of experiencing particular situations and a common attitude of responding to external stressors.

The PSS (see Additional file 1) is one of the few instruments to measure a global level of perceived stress, dealing with the degree to which situations in one's life are appraised as stressful as opposed to the presence of particular stressors. It is a 14-item instrument that assesses perceived stressful experience or stress responses over the previous month using 5-point Likert type scales. Total possible scores are from 0 to 56. Higher scores represent high stress levels. The PSS is a well established measure. The creators reported convergent validity indicated by relationships with depressive (r = .76, n = 332) and physical (r = .70, n = 64) symptomatology scales. Internal consistency reliability was high with Cronbach's alpha coefficient ranging from .84 (n = 332) to .86 (n = 64) [1]. It has been used in a range of settings and shown to relate to a number of physiological and psychological correlates of stress [7–11]. The PSS has been utilised for evaluating the effect of interventions to reduce stress [12] and has been used as a reference standard for examining validity of new stress measures [13].

The PSS has already been translated into several languages including Spanish [14], Swedish [15] and Chinese [16]. There is no validated Japanese version of the PSS although subsequent to the commencement of this study Japanese translations of the scale have been reported but not subjected to validation ([17] for example). Thus it has particular value in cross-cultural studies to develop a Japanese version of the PSS since it has been used in a wider range of cultures than most measures. Therefore, we developed the PSS-J (see Additional file 2). A small pilot study [18] suggested the reliability and equivalence in terms of factor structure between the PSS and the PSS-J although the sample size was too small to draw firm conclusions. The present study further tested these properties using a much larger sample. Permission to translate the PSS into Japanese was granted by the developer, Professor Sheldon Cohen. The study was conducted under the aegis of a wider study, which had been ethically scrutinised and approved by the authors' institutional ethical committee.

The factor analysis revealed that for the original PSS, all the items of negative experience loaded highly on the first factor. Although some items reflecting positive experience were also strongly related to the first factor, these items also had substantial correlation with the second factor. This pattern of factor structure is nearly identical to that identified by previous empirical research. Cohen and Williamson [21] showed a two-factor structure for the PSS in a US sample (n = 2387) and each factor reflected positively or negatively phrased items. Subsequent studies confirmed this factor structure in psychiatric patients in Canada (n = 96) [24] and in psychology students in Mexico (n = 365) [22]. In the current study as well, the first factors can be labelled as "negative perception" and the second factor as "positive perception." As mentioned above, however, Items 7, 10 and 13 highly loaded on the first factor in spite of positive statements. This might be due to a relatively small sample size (n = 222) for factor analysing the 14-item scale. In the study by Hewitt et al. (n = 96) [24], factor loading was not reported about Items 10, 12 and 13 which might be differently grouped in terms of factorial nature.

On the other hand, as for the PSS-J, all items stating positive attitude were highly related to the first factor and all items of negative attitude to the second factor. Thus, labels for these factors can be "positive perception" and "negative perception" respectively.

The variance explained by the factor is somewhat different between the two cohorts in the current study, and also from that found in these previous studies. The first largest factor explained 42.7% and the second factor 11.0% in the UK sample, and 23.8% and 18.8% respectively in the Japanese sample in the current study. Previously reported variance was: 25.9% accounted for by the first factor and 15.7% by the second factor in the US sample [21]; 31.4% and 15.2% respectively in the Canadian sample [24]; and 32.6% and 15.4% in the Mexican sample [22]. Such dispersion might be derived from cultural differences and different sample size.

Comparing the factor loading of the PSS and the PSS-J, although the magnitude of each factor was different, items stating positive attitude were gathered in the "positive perception" factor and items of negative attitude were in the "negative perception" factor for both scales. Also, the factor congruence coefficient indicated satisfactory factor agreement between the PSS and the PSS-J. It can be seen that the PSS and PSS-J were similar in factor structure. Cronbach's alpha for each factor was high. This suggested that all factors were internally consistent. The equivalence between the PSS and PSS-J was supported through a similar factor structure and factor loading on items. However, as pointed out by Cohen and Williamson [21] and González and Landero [22], the distinction between the two factors is considered irrelevant and total scores obtained by summing responses to all 14 items should be used for the purpose of measuring perceived stress.

Regarding both the PSS and PSS-J, all the items except for one (Item 12 in the PSS; Item 4 in the PSS-J) indicated acceptable item-total correlations. Generally, items showing an item-total correlation of 0.3 or lower are considered to be dropped from the scale [27]. However, a scale with an acceptable Cronbach's alpha may still have one or more items with low item-total correlations [27]. Thus, the findings of the current study were indicative of sufficient item-total reliability for the PSS and PSS-J.

As described in the translation section, a number of efforts were made to produce a Japanese version of the PSS as equivalent as possible to the original scale. Using intimate couples of a native English speaker and a native Japanese speaker probably contributed greatly to addressing problems that are likely to occur when an instrument is translated into other languages. These would include conceptual problems such as differences in conceptualisation and behaviours associated with the construct of a scale and inappropriateness of item content, and linguistic problems such as erroneous literal translation and poor wording [19, 20]. Multiple forward and backward translations and verification of the equivalence between the source and final version by a multi-disciplinary reviewer panel would also resolve these issues. However such couples are likely to differ from the population in general. The translation might, therefore, be biased although professional translators and those who generate the original items on such scales are equally unlikely to represent the general population.

While the sample size was large, another limitation of this assessment is that the subjects consisted of undergraduate nursing and pharmacy students who were recruited from a single institution in each country. Also, they were predominantly female. The findings may, therefore, be influenced by stress characteristics unique to them such as gender, stressors as a consequence of actually being undergraduates or particular factors relating to the subject of study. Further equivalence assessment using a sample that is more representative of the population in general would ideally be conducted to overcome these limitations. Certainly it is important that research using this scale in new population assesses the factor structure and internal consistency for its own sample.

In addition to the small-scale preliminary test [18], this study further supported the equivalence between the PSS and PSS-J through analysing factor loadings on items, factorial agreement and internal consistency. We conclude that the PSS-J is a suitable tool for the study of perceived stress among native Japanese speakers and that there is sufficient evidence of the equivalence of the PSS and PSS-J to consider them as equivalent in cross-cultural studies.