An Instrument for Assessing Evolutionary or Distal Causes of Psychiatric Disorders: Psychometric Properties of Persian Version of Evolutionary Fitness Scale

Background: Evolutionary perspectives have recently received significant attention for better understanding psychological disorders and providing effective interventions. Evolutionary perspectives have been very effective in studying psychological disorders to help consider the distal causes of such disorders. Objectives: This study aimed to investigate the psychometric properties of the Persian version of the Evolutionary Fitness Scale (EFS) among Iranian students. Methods: The statistical population included students studying at the Iran University of Medical Sciences in 2019 - 2020. In total, 266 students were selected using a convenience sampling method. The participants completed the EFS, Depression, Anxiety, and Stress Scale (DASS-21), and Rosenberg’s Self-esteem Scale (RSES). The EFS reliability was assessed by internal consistency and test-retest. The validity was evaluated by convergent and divergent validity and confirmatory factor analysis (CFA). The data were analyzed using SPSS 24.0 and LISREL 8.80. Results: The CFA demonstrated that the two-factor model of the EFS (personal adaptedness and partner and offspring fitness) had a suitable fitting. This scale had significant negative and positive correlations with DASS and RSES, respectively. Internal consistency was obtained using Cronbach’s alpha: 0.96 for personal adaptedness, 0.94 for partner and offspring fitness, and 0.97 for the whole scale. Test-retest reliability was 0.81 for personal adaptedness, 0.80 for partner and offspring fitness, and 0.83 for the whole scale. Conclusions: This study could complement the cross-cultural literature on EFS by examining its construct, convergent, and divergent validity and reliability. The EFS had good validity and reliability among students. Thus, it could be a suitable tool in research and clinics.