Psychometric evaluation of the modified Kessler seven-item version (K7) for measuring psychological distress using Rasch analysis: a cross-sectional study in a rural district of Bangladesh

Objectives: This investigation expected to validate the psychometric properties of the modified seven-item Kessler psychological distress scale (K7) for measuring psychological distress in healthy rural population of Bangladesh.

Design: Cross-sectional study.

Setting: Narail district, Bangladesh.

Participants: A random sample of 300 adults of age 18-90 years were recruited. Face-to-face interviews were conducted between July and August 2018 using an Android phone installed with a mobile data collection application known as CommCare.

Outcome measure: Validation of the K7 was the major outcome. Sociodemographic factors were measured to assess for Differential Item Functioning to check if the tool functions equally in different factors. Rasch analysis was carried out for the validation of the K7 scale in the healthy rural population of Bangladesh. RUMM2030 was used for the analyses.

Results: Results showed good overall fit, as indicated by a non-significant item-trait interaction (χ²=44.54, df=28, p=0.0245) compared with a Bonferroni adjusted p value of 0.007. Both item fit (mean=0.30, SD 1.22) and person fit residuals (mean=-0.18, SD 0.85) showed perfect fit. Reliability was very good as indicated by a Person Separation Index=0.85 and Cronbach's alpha=0.89. All individual items were ordered thresholds. The K7 scale showed adequate reliability, unidimensionality and was free from local dependency. The K7 scale also showed similar functioning for adults and older adults, males and females, no education and any level of education, and at least some financial instability versus no financial instability.

Conclusions: Validation of K7 scale confirmed that the tool is suitable for measuring psychological distress among the rural Bangladeshi population. Further research should validate the K7 scale in different rural settings in Bangladesh to determine a valid cut-off score for assessment of severity levels of psychological distress. The K7 scale should also be tested in other developing countries where sociodemographic characteristics are similar to those of Bangladesh.