Background: Four dimensions of inner strength were previously identified in a metatheoretical analysis: firmness, creativity, connectedness, and flexibility.Objective: The aim of this study was to develop an Inner Strength Scale (ISS) based on those four dimensions and to evaluate its psychometric properties.Method: An initial version of ISS was distributed for validation purpose with the Rosenberg Self-Esteem Scale, the Resilience Scale, and the Sense of coherence Scale. A convenience sample of 391 adults, aged 19 to 90 years participated. Principal component analysis (PCA) and confirmatory factor analysis (CFA) were used in the process of exploring, evaluating, and reducing the 63-item ISS to the 20-item ISS. Cronbach's alpha and test-retest were used to measure reliability.Results: CFA showed satisfactory goodness-of-fit for the 20-item ISS. The analysis supported a four-factor solution explaining 51% of the variance. Cronbach`s alpha on the 20-item ISS was 0.86, and the test-retest showed stability over time (r = 0.79).
Conclusion:The ISS was found to be a valid and reliable instrument for capturing a multifaceted understanding of inner strength. Further tests of psychometric properties of the ISS will be performed in forthcoming studies.
What this paper adds A new scale, the Inner Strength Scale, has been developed to estimate the four dimensions of firmness, creativity, connectedness, and flexibility. The Inner Strength Scale was found to have satisfactory validity and reliability. The Inner Strength Scale was found to be applicable to men and women of various ages.