CONSTRUCT VALIDITY AND RELIABILITY OF PERCEIVED STRESS SCALE (PSS-14) IN A ROMANIAN SAMPLE OF DENTAL STUDENTS

Abstract

Abstract The purpose of this study was validation and examination of the PSS-14 psychometric characteristics, one of the most renowned tests measuring perceived stress, on a group of dental students (N = 250; 147 females and 103 males; Mage = 22,84; S.D. = 1,79), using descriptive, correlational and confirmatory factor analyzes (CFA). [...]PSS-14 showed adequate properties for perceived stress scale assessment, so that it may contribute to the study of perceived stress for dental students. 3.RESULTS a.Factorial structure Based on the information obtained from previous studies regarding the PSS14 structure, we started the confirmatory factor analysis (CFA) using the indexes announced in the static analyses paragraph. Since Mardia coefficient is 26.29, with a critical ratio of 8.42, higher than the admitted value of 1.96, 2,000 bootstrapp samples were applied to prove non-normality. [...]model 3 is calculated for two factors without item 9.

Headnote

Abstract

The purpose of this study was validation and examination of the PSS-14 psychometric characteristics, one of the most renowned tests measuring perceived stress, on a group of dental students (N = 250; 147 females and 103 males; Mage = 22,84; S.D. = 1,79), using descriptive, correlational and confirmatory factor analyzes (CFA). The two-factor scale structure without item 9 is supported by CFA, providing to this model a good fit. Convergent validity is supported by association with tests appreciating life satisfaction (SWLS) and depression, anxiety and stress under pressure (DASS-21R). PSS-14 shows an acceptable assessment regarding internal consistency (Cronbach's a - 0.79 for both subscales obtained). Consequently, PSS-14 showed adequate properties for perceived stress scale assessment, so that it may contribute to the study of perceived stress for dental students.

Keywords: PSS-14, validation, CFA, dental students.

1.INTRODUCTION

During the last decade, a significant increase was observed in the number of dental students [1-8]. A comparative image of different categories of students proves that the stress of dental students is much higher compared, for instance, with engineering [9,10] or social sciences students [11]. Going through the academic curricula necessary to build-up the knowledge for dentist profession implies intellectual effort and physical resistance in view of actively participating in the activities/ requirements imposed for reaching high performance.

Literature approached a complex image of stress for medical dental students, identifying stress symptoms and predictors, stress indicators, personal factors and stress management [3,5,7]. The Romanian literature on stress in dental students offers studies regarding the primary sources for the stress perceived in the dental academic environment [12,13], stress assessment in association with stress related sociodemographic factors [14], such as: burnout [15], anxiety, depression and irrational beliefs [11], stress relation with well-being [13]. Nevertheless, the analysis and validation of some stress assessment questionnaires in the dental environment is modest. Literature investigation only shows validation of PSS-10 questionnaire on an extended lot of general medicine students [16].

The objective of the present work is PSS-14 validation in a dental students group. To the best of our knowledge, this is the first PSS-14 validation study in dental students in Romania.

PSS-14 description

One of the mostly used instruments in measuring perceived stress is PSS-14, together with the same family tests, PSS-10 and PSS-4 [17]. Generally, scale versions with 10 and 14 items have high methodological sensitivity and good construct validity, while PSS-4 has a lower fidelity than the first two versions [18-20].

PSS-14 has 14 items requesting respondents stress assessment over the last month on a scale from 0 - Never to 4 - Very often. Out of the 14 items, 7 are assessed negatively. If, during early studies [21], PSS-14 was used for calculating only one general stress factor, subsequent factor analytical studies distinguished 2 latent factors in most versions [20]. The first factor (1, 2, 3, 8, 11, 12, 14) has negative items and was treated under stress [22], negative stress [23,24], perceived stress [25] and perceived helplessness [26]. The second factor (items 4, 5, 6, 7, 9,10,13) has positive items and was considered as counter stress [22], positive stress [23, 24], perceived control [25] or perceived self-efficacy [26].

The scale introduced empirical evidence for its validity and fidelity in several cultural contexts, including China [18,27], Jordan [28], Brazil [29], Sweden [30], Greece [23], Germany [31], both for general population [18] and for specific population categories, from students and professors [28], resident physicians [32], to patients hospitalised in psychiatry units [33] and smokers [27]. PSS-14 was correlated with anxiety and depression scales, such as PHQ-anxiety, PHQ9, emotional distress - scale GHQ12 [26] and negatively with mental health scales [34].

Cohen et al. reported an a coefficient of 0.78 for the general population and of 0.85, respectively, for students [17]. Moreover, Cohen and Wiliamson [21] and Cohen et al. [17] reported 0.85 test-retest fidelity test after two days and 0.55 within 6 weeks. In all studies, the internal consistency measured by Cronbach's alpha was more than 0.70 for different samples, such as professors [28], students [36], adult general population [18]. Other studies show that, for medical residents population, composite reliability of the two factors was over 0.80 [32]. A Romanian version of the PSS-14 applied to the general population (N = 928) from 3 large regions of the country showed an acceptable internal consistency coefficient of 0.74, calculated for the total score [37]. A recent study made on a subject sample of the general population finds similar results, that materialize a few of the psychometrical characteristics of the test, and also a Cronbach's alpha value over 0.70 for the total score [38].

2.MATERIALS AND METHODS

Participants and procedure. The sample group included 250 students from the Faculty of Dental Medicine of the University of Medicine and Pharmacy - Bucharest, Romania, aged between 20 and 31 years (M = 22,84; S.D. = 1,79), 147 females and 103 males, with no significant age difference. The sample was built in a probabilistic manner, by applying the scale to groups of students in the 1st, 3rd and 6th BA years. The data was collected in the academic year 2018-2019 during didactic activities at two week distance from each test application. Students were informed that participation is voluntary, anonymous and unpaid. The set of instruments applied during the didactic activities lasted nearly 15 minutes. We also mention that we avoided the application of the stress perception measurement test around the exam session. The study was ethically approved by the University Ethical Commission as part of the 94/2016 Protocol, being performed compliance with the Helsinki Declaration.

Instruments

1. Stress perception scale - PSS-14 (Cohen and Wiliamson) [21] - self-administered instrument exploring stress subjective feeling over the last month by 14 items, of which 7 are reverse, measured on a scale from 0 - Never to 4 - Very often. Sample item: During the last month, how often have you been upset because of something that happened unexpectedly? The total perceived stress score may vary between 0 and 56, the high scores reflecting a high perceived stress during the last month.

2. Depression Anxiety Stress Scales - DASS21-R (Lovibond and Lovibond) [39] measures the negative emotional states in case of depression, anxiety and conceptualised stress under pressure; each subscale has 7 items, appreciated on a continuum from 0 - Did not apply to me at all, to 3 - Applied to me very much or most of the time. Cronbach's a for each of the 7-item subscales (Depression = 0.88, Anxiety = 0.82; Tension/ Stress = 0.85) indicated high internal consistency and reliability for a group of dental students [40]. The internal consistency obtained for this case is considered good, the a Cronbach coefficients obtained being: 0.85 - depression, 0.89 - anxiety and 0.86 - tension/ stress.

3. Satisfaction with Life Scale - SWLS (Diener, Emmons, Larsen, & Griffin) [41] assesses life satisfaction - considered to be the cognitive component of subjective well-being. The scale is a short 5-item instrument with a 7-point Likert style response scale. Sample item: The conditions of my life are excellent. Studies showed that SWLS correlates with happiness and negatively with anxiety and stress [42], depression [43], dispositional optimism and sleep quality [44]. Most studies mention the presence of fidelity indexes over 0.70. In this research, we obtained a = 0.78 for the total score of SWLS.

Statistic strategies used the confirmatory factor analysis (CFA) to check the factor structure. For the last one, we used the following statistic factors: x2 value, df (degrees of freedom), x2/df, (goodness-of-fit index), AGFI (adjusted goodness-of-fit index), TLI (Tucker-Lewis index), CFI (comparative fit index), RMSEA (root mean squared error of approximation), SRMR (standardized root mean square residual). For value x2/ the exigency of 2.00 according to Byrne [45] was used. CFI and TLI values close to 0.90 or higher are acceptable to good. RMSEA and SRMR should preferably be less than or equal to 0.05 [46]. Internal consistency was calculated with a Cronbach indexes. Convergent validity was tested by bivariate correlations between PSS-14 and questionnaires SWLS and DASS21R. The analysis was led with SPSS v22 and Amos v20 Programs (IBM, New York, NY, USA).

3.RESULTS

a.Factorial structure

Based on the information obtained from previous studies regarding the PSS14 structure, we started the confirmatory factor analysis (CFA) using the indexes announced in the static analyses paragraph. Since Mardia coefficient is 26.29, with a critical ratio of 8.42, higher than the admitted value of 1.96, 2,000 bootstrapp samples were applied to prove non-normality. The first model was calculated for only one factor (single-factor). The second model was calculated for two factors. In this model, it was noticed that item 9 (.Felt able to control irritations in your life?) has a factor loading of 0.34; therefore it was eliminated. Consequently, model 3 is calculated for two factors without item 9.

Table 1 summarized the fitness indexes for the 3 calculated models: Ml - the single-factor solution is the weakest. Although, x2/df has an acceptable value, the rest of the fitness indexes are very weak; М2 - the two-factor solution without correlated errors (j2 = 116.816; df = 76; X2/df= 1.53; CFI = 0.93; GFI = 0.90; AGFI = .86; TLI = .92; RMSEA = 0.058 - CIg0%: 0.036 - 0.078; SRMR = 0.0668, p = 0.002). In this model, x2/df has a good value, while CFI, TLI and GFI are still acceptable. Model M3 is superior to the other two. This also includes two factors without item 9 and one correlated error between items 11 and 12 from factor 1 (j2 = 69.65; df= .63;j2/df= 1.10; CFI = .98; GFI = .93; AGFI = .90; TLI = .98; RMSEA = 0.026 - CIgo%: 0.000 - 0.056; SRMR = 0.0567, p = 0.264). The model was maintained for further analyses.

In the case of factor 1, of negative stress, two items have a very good loading (more than 0.80), two others have a loading of more than 0.45 and one item is weak (0.37). For factor 2, of positive stress, out of 7 items, two have a very good loading (more than 0.70), 4 items have a good loading (more than 0.58) and one has more than 0.45 loading. Item 12 has the lowest loading per factors (0.37), which suggests that an item has a weak correlation with the extracted factor. A significant negative moderated crosscorrelation (r = -0.41; p = .001) was obtained between the positive stress factor and the negative one.

b.Descriptive statistics

The descriptive statistic was examined for each item by average, standard deviation, skewness and kurtosis. Regarding the internal consistency, Cronbach's alpha coefficients of more than 0.79 for both subscales (CI95% - 0.73 - 0.83 - Negative stress factor; 0.74 - 0.84 - Positive stress factor) suggest a good internal consistency of the scale. An extra confirmation of the test qualities results from the calculation of composite reliability by Raykov's formula, where A = the standardized factor loadings of the items and £ = the error variance of the items [47]. Therefore, the CR score for the first Negative stress factor is 0.81, and for Positive stress factor is 0.79.

(ProQuest: ... denotes formula omitted.)

The corrected item-to-total correlation method was used to check the relation between each item and the total scale. All items are higher than 0.40, except for item 12, that is to the limit: 0.40.

c.Convergent and divergent validity

In this context, we intend to investigate the criterion validity by inspecting the convergent and divergent validity with other psychological concepts, such as: depression, anxiety, tension/ stress and life satisfaction. Significant relations between the two PSS-14 factors with the related concepts (tension/ stress), correlated with stress (depression and anxiety) and with life satisfaction concept, were anticipated. As shown in Table 3, the negative stress factor from PSS-14 correlates significantly positively with the tension/ stress scales (r = 0.66), depression (r = 0.64), anxiety (r = 0.59), and negatively with life satisfaction (r = -0.31) (all at p < .01).

The positive stress factor weakens the reverse correlations with tension/ stress (r = -0.35), depression (r = -0.27), anxiety (r = -0.29) and positive with life satisfaction (r = 0.46) (all at p < .01).

4.DISCUSSION

The study aimed at testing PSS-14 validity and fidelity within a group of Romanian dental students, even if the properties of the test have not been yet analysed on the population here considered. First, we intended to establish if the factor structure with two factors fits the group of dental students. Secondly, it was important for us to establish if PSS-14 has good psychometrical properties. CFA was done to compare singlefactor and two-factor models, with and without item 9. The values of the obtained indexes showed that the model without item 9 was superior.

In the case of this last model, the factor loading was good (between 0.45 and 0.83 for factor 1 and between 0.46 and 0.80 for factor 2), except for item 12 (...found yourself thinking about all the things you have to accomplish), with the weakest factor loading of 0.37. Moreover, Ribeiro Santiago et al. showed, by applying the Rasch model, that both item 12 and item 9 indicate strong misfit on a sample of 3857 Australians [25], while Huang et al. evidenced in the executed CFA that item 12 is problematic, namely it is loaded on both stress factors, both the negative and the positive one [18].

The negative correlation between the two factors of the scale (r = -0.41) also supports the structure of the PSS-14 present version. Therefore, the two stress factors are related, but distinct.

The result for the consistency indexes obtained (0.79 for both factors) and the composite reliability score (0.79 and 0.81) is in line with most studies, showing a good internal consistency for PSS-14 [18,23,28,35]. For instance, a study on medical residents obtains Cronbach's alpha indexes higher than 0.90, composite reliability being 0.86, respectively 0.89, for the two factors [32].

The result of the correlations between perceived stress factors and depression and anxiety was to be expected, as long as all studies proved, for some time, the relation between those variables [4,11,19,40,48,49]. This result suggests that the perceived stress is related to mental health problems. At this point, there is both a similarity and a difference with the study of Andreou et al., which reports only the correlations of the PSS-14 total score with DAS21-R [19]. The direction and intensity of correlations between the total score at perceived stress and depression (r = 0.66), anxiety (r = 0.54) and tension/ stress (r = 0.64) registered in their study corresponds to those obtained in our present study for the negative stress factor (r =0.64, 0.59 and, respectively, 0.66) [19]. In turn, for the positive stress factor, we obtained moderate negative correlations with DASS 21-R (r =-0.35, -0.27 and, respectively, -0.29) scales.

As expected, the relation between the negative stress factor and life satisfaction is a negative one (r = -0.31), while the positive stress factor makes a significant positive correlation (r = 0.46) with life satisfaction. Previous studies [50,51] showed that the perceived stress is a significant predictor for the low level of life satisfaction. A study on medical and dental students (medicine, dentistry, nursing and speech therapy) performed in Bosnia and Herzegovina showed that higher levels of perceived stress predispose subjects to a lower quality of life [49].

No other correlations between the perceived stress factors and the socio-demographic characteristics of the participants, such as age and year of study, were found.

Limitations of the study: Certain limits of the research must be considered, as it was done in only one Romanian university, so that the results cannot be generalized for other dental education institutions. Subsequent studies involving various groups of dental students from different geographical areas should be therefore considered in the future. Moreover, the study is limited by its sample size. For extended results, a larger number of students are necessary in further investigations.

5.CONCLUSIONS

The study brings new evidence in favour of the PSS-14 psychometric properties for Romanian dental students. Consequently, it may contribute to perceived stress study for dental students, where item 9 is excluded, thus remaining 13 items. However, precaution when applying the test is necessary, mainly as to the aspects explained regarding item 12, and correlated with previous studies. PSS-14 investigation in association with other stress measurement scales and other related instruments is required for the future. Further phases include test administration in various populations from the the dental environment: doctors, nurses and patients.

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