Perceived Stress Scale (PSS-10) psychometric properties in migrants and native Germans

Mental health and specifically stress have gained attention as public health concerns by the European Regional Office of the World Health Organization (WHO) and by the German national government. Objective 1 of The European Mental Health Action Plan 2013–2020 [1] focuses on equal opportunities for mental health well-being, specifically recognizing vulnerable or at risk groups. The Stress Report Germany 2012 [2] echoes the importance of bringing attention to and researching the impacts of stress and mental health, especially in the ever-changing work environment. The Stress Report Germany 2012 [2] found that perceived stress and the number of health complaints increased from the 2005/2006 report. Most importantly, both the WHO European Regional Office and Stress Report 2012 emphasize the inequality of how stress and mental health impact various groups, particularly vulnerable and disadvantaged groups which may be characterized by ethnicity, sex, age, religion, sexuality, refugee or immigrant status, socioeconomic status and physical and/or mental disability [1, 2].

Germany has a rich immigration history that has led to the diversity of its population. Work-visa programs from the mid-1950s until 1973 explain, in large part, the earlier settlement of Italians and Spaniards, but also the Turkish, Polish and Romanian populations within Germany [3, 4]. In more recent years, immigration flows consisted not only of economic migrants, but increasingly people fleeing persecution and war-torn countries. The total foreign population in Germany in 2014, including EU28, is reported at just over 8 million [5]. Citizens of Turkey (11.2%), Poland (8.6%), Syria (7.1%), Romania (6.9), and Italy (5.1%) represent the highest percentages of the foreign-born population of Germany in 2018 [6].

Migrants (first- and second-generation) have long been a focus of stress research. Regardless of whether migration occurred voluntarily or as a result of natural disasters or displaced by conflict, many aspects of the migration process are seen as stressors [7]. Even after settling in a new country, those who have migrated may still experience stress as they adapt to their new home through acculturation and integration stressors [8]. In Russian and Iranian migrants in Germany, Haasen, Demiralay, and Reimer [9] found a significant correlation between acculturative stress and mental distress; the length of residency in Germany did not have a significant effect. Therefore, it is important to take a closer look at stress within the population of residents with a migration background [10]. However, it is not known, if generalized mental health or stress are also responsive to migrant specific stressors such as integration, discrimination, acculturation or PTSD. Therefore, it is important in advancing stress research to test whether widely used scales maintain psychometric strength and measurement equivalence in migrant specific populations.

Within the German population, only a few studies exist testing the measurement equivalence of mental stress measures between populations with and without a migration background. Tibubos et al. [11] demonstrated strict measurement invariance of the Patient Health Questionnaire-9 between migrant status (nonimmigrants, 1st generation migrants and 2nd generation migrants) and country of origin in a German cohort study, the Gutenberg Health Study (GHS), with 13,973 participants. In another study with N > 26,000 participants from the German Socio-economic Panel (SOEP) including nonimmigrant, migrant and refugee populations in Germany from 16 different countries, the Patient Health Questionnaire-4 and the Short Form Health Survey (SF-12) showed scalar invariance (1) between men and women, (2) between groups stratified by migration status, (3) between survey languages, (4) between country of origin, (5) between sex and country of origin, and (6) between age groups [12].

The Perceived Stress Scale developed by Cohen, Kamarck and Mermelstein [13] is a widely used self-report measure assessing “the degree to which situations in one’s life are appraised as stressful”(p.387). The scale measures, over the past month, the degree to which life has been experienced as unpredictable, uncontrollable and overloaded. The original scale included 14 items but was later reduced to 10 items due to low factor loadings on 4 items; this change marginally improved the scale reliability shown via Cronbach’s alpha [14]. An additional 4 item version was developed for telephone interviews or situations with time restrictions [14], however, this short form has not fared as well as the full 14- and 10-item versions [15]. In a review of the PSS psychometric properties, Lee [15] showed across the 19 studies included, the PSS-10 was found to be superior to the 14-item version. Cronbach’s alpha constantly surpassed the standard .70 threshold ranging between .74–.91 [15]. The review also found consistent results supporting a two factor structure, which is in contrast to the original one-factor structure presented by Cohen et al. [13]. This debate was sparked after Hewitt, Flett and Mosher [16] challenged the one-factor structure, recognizing that both factors explained unique variances of depression and that factor 1 comprised of ‘adaptational symptoms’ while factor 2 reflected ‘coping ability’. Roberti, Harrington and Storch [17] further supported the two-factor structure naming factor 1 perceived helplessness (PHS) and factor 2 perceived self-efficacy (PSES). The 10-item version has proven to be a valuable tool for stress research as it maintains consistent test-retest reliability across various timespans, acceptable Cronbach’s alpha, and strong factorial validity in measuring perceived stress across various populations and languages [18‐22]; see review: [15]. Although the PSS-10 has been used in specialized populations, in particular minority groups, many psychometric studies on the PSS-10 call for continual testing in more diverse and representative populations [15, 18].

In a representative German population, Klein et al. [23] tested the translated German version PSS-10 showing a strong Cronbach’s alpha = .84, further emphasizing the strength of the scale’s internal consistency. Reis and colleagues [24] tested the factor structure of the German version PSS-10 using bifactor modeling bringing a deeper understanding to the multidimensionality of the scale. Most recently, Schneider et al. [25] tested the PSS-10 two-factor structure between clinical and nonclinical samples, showing strict measurement invariance. Although the PSS-10 has been translated and tested in numerous languages, populations and contexts, the psychometrics of the German version PSS-10 have not been tested for migrant populations within Germany. Considering the popularity of the PSS-10 as a generalized measure of stress and its various applications, this study aims to fill this gap by testing the validity, reliability, and measurement equivalence of the German version PSS-10 between native Germans and migrants.

Lee [15] called for validating the PSS in representative populations and Klein et al. [23] responded by testing the German version PSS-10 in a representative German population. The current study took the analysis in the same sample one step further by testing whether the German version PSS-10 is also a reliable and valid measure of perceived stress in a migrant sample.

Overall the PSS-10 maintains a two-factor structure that is strictly invariant between German natives and migrants, it additionally shows good internal consistency as found in other diverse populations, see review [15]. Omega and Cronbach’s alpha for the PSS-10 sub-scales ranged from .83 to .85 thus supporting the reliability of the German version PSS-10. Migrants reported higher scores on both PSS sub-scales, indicating higher levels of perceived helplessness as well as lower levels of perceived self-efficacy since the latter scale is reversed. However, by taking into account Cohen’s d effect size, there is no relevant effect between the two samples on PHS or PSES.

When comparing first- and second-generation migrants, perceived self-efficacy showed no significant difference, however, first-generation migrants report significantly lower perceived helplessness scores with a small effect size. Although this finding is modest, it is at odds with previous literature, which generally show that first-generation migrants report higher rates of mental distress compared to natives and second-generation migrants [10, 11]. Factors of language skills, unemployment, perceived discrimination, integration or acculturation, and cultural barriers often reveal differences between first- and second- generation migrants [10, 11, 42]. It is important to note the sample size of the current study, as first-generation migrants make up a very small proportion of total migrant sample (n = 76). While the second-generation sample may still emulate representative characteristics (n = 252), it is unlikely that 76 migrants represent the linguistic, religious, and cultural diversity of the first-generation migrants residing in Germany. For many first- and second- generation migrants, the cultural background plays an important role. For instance, migrants of Turkish origin report higher rates of depression, anxiety, and suicidal ideation compared to Polish origin migrants and German natives [10]. Similarly among first-generation migrants, Tibubos et al. [11] illustrate that those with a Turkish origin report higher rates of mental distress symptoms compared to other geographical origins. Self- and group- attribution as migrants are additional factors that may influence not only differences between migrants and native Germans, but also differences between first- and second-generation migrants. Nesterko et al. [43] explored attribution as a migrant as a predicting factor of PTSD, depression and anxiety, finding that many second-generation migrants do not self-attribute as a migrant. These types of factors are likely to influence perceptions of discrimination and ultimately levels of perceived stress.

With respect to the PSS-10 factor structure, the ongoing one- or two-factor debate led this study to test the scale factor structure using an EFA specifically in the migrant sample. Results showed a two-factor solution with good factor loadings, thus reflecting the established two-factor structure presented by Hewitt et al. [16] and Roberti et al. [17], where negatively worded items represent factor 1 (perceived helplessness) and positively worded items make up factor 2 (perceived self-efficacy). Item-rest correlation values are generally consistent across the native and migrant samples, emphasizing that items fit to the total scale similarly across the samples. Separate group-specific CFA and combined MGCFA model fit indices were in line with the recommended values of Schermelleh-Engel, Moosbrugger, & Müller [35]. Therefore, the current two-factor structure shows adequate model fit in the native and migrant samples.

As for measurement invariance, the two-factor model is strictly invariant between German natives and migrants. Given that χ² is sensitive to large sample sizes and violations of normality [33, 36, 37], with a total sample of N = 2523, it was expected to be significant showing poor model fit. Chen [37] discusses similar biases caused by large or unequal sample sizes in evaluating measurement fit indices; as with increasing sample size, the standard deviations of fit indices will decrease leading to higher chances of rejecting the model. Additionally, unequal samples may conceal non-invariance as the larger group will dominate calculations of many fit indices, leading to small changes between invariance models [37]. This is likely the case with the current samples, ultimately showing very low changes in all fit indices across models. Even so, considering that the data violates normality and has a large, particularly unequal, sample size, ΔCFI, ΔSRMR and ΔRSMEA still meet strict invariance.

Despite this study’s support of the two-factor structure and results of others showing independent explanatory power of the individual factors [24], the general PSS total scale also consistently demonstrated good Cronbach alpha values offering a simplified interpretation of perceived stress [15]. Klein et al. [23] report good internal consistency for the German version PSS-10 total scale (Cronbach alpha = .84). Cohen and Williamson [14] challenge the content relevance of the second factor and Reis et al. [24] rather argue for a bifactor solution where each factor is content relevant. Given these contradicting results it is difficult to recommend using one single solution for all analyses – rather, while many studies find two factors, the total PSS score may still be appropriate. Therefore, as Reis et al. [24] elaborate, the decision of implementing the total score or sub-scales depends highly on the research focus, furthermore one must take caution when interpreting means of the total score as well as covariances or correlations with other concepts.

Although the PSS-10 was not intended to operate as a diagnostic measure [44], the scale may signal early signs of mental distress for a broad range of stressful living conditions. Perceptions of helplessness and self-efficacy are key factors in stress processes and stress regulation [25]. In clinical settings, it could be used to adjust stress management strategies, understand worsening symptoms due to stress, and facilitate the development of coping skills [13, 17, 18]. Schneider et al. [25] support the use of the German PSS-10 in clinical populations as a first-screening instrument. Potential clinical applications of the German PSS-10 are relevant for residents with a migration background as it may identify individuals with heightened levels of stress, indicating potential risk factors for other mental health concerns.

Overall, the German version PSS-10 is a valid, strictly invariant and reliable measure of perceived stress among German natives and residents with a migrant background. These results are valuable as implications of the PSS-10 can aid German health officials as well as stress researchers to understand stress in migrant populations in Germany.

This study tested the validity and reliability of the two-factor structure of the German version PSS-10 and measurement invariance in native and migrant subsamples. The key conclusions are: (1) the German version PSS-10 is suitable for comparing German residents with and without a migration background. (2) Despite good internal consistency for the total scale, the PSS-10 measures two aspects: (a) perceived helplessness and (b) perceived self-efficacy. Future research would profit from analyzing the two subscales separately, not only using the total score.