In order to evaluate the content validity of qualitative data, the initial draft of the instrument was examined by 15 experts in statistics, epidemiology, religious sciences, aging, and health to find the difficulty, the degree of inconsistency, ambiguity of expressions, or inadequacy in the meaning of words. Also, the relative content validity ratio (CVR) and content validity index (CVI) were used to evaluate the content validity of quantitative data. Calculating the CVI helps the researcher to ensure the selection of the best and most important content statistically (
9). In this stage, 15 experts were asked to determine whether an item is essential to operationalize the theoretical construct. The numerical value of the CVR was determined using the Lawshe table. Calculating the CVI indicates whether the item is best designed to measure the construct (
11). Therefore, in the present study, the panel of experts was asked to examine each item in a four-point spectrum (unrelated, needs serious review, relevant but needs review, and fully relevant). The CVI score of above 0.79 for each item was confirmed in terms of content validity. Finally, the face validity of the instrument was evaluated by the experts and also distributed among 15 elderly at the beginning and before conducting the main study. In order to evaluate the face validity qualitatively, the terms and expressions were examined in terms of non-repetition, comprehensibility, shortness, etc., from the perspective of the target community (the elderly). To determine the face validity quantitatively, the items were compiled and provided to the target group as a table with a five-point Likert scale ranging from ‘completely important’ (five points) to ‘not important at all’ (one point) and the impact of the item was calculated. In the item impact method, if the impact score of each expression is equal to or greater than 1.5, the expression is recognized and retained as appropriate for subsequent analysis (
11). Factor analysis was used to evaluate the construct validity. In the current study, EFA was used to investigate the internal relationship between the variables and to discover the classes of variables that are most related to each other. The principal component analysis method and the Varimax orthogonal rotation method were used for exploratory analysis with a factor loading of more than 0.3 and based on Kaiser Meyer and Olkin (KMO) value and Bartlett’s test of Sphericity. Moreover, in order to check the criterion validity, concurrent criterion validity was used. For this purpose, the designed instrument for the spiritual health of the elderly and the criterion instrument were completed simultaneously by the elderly. Paloutzin and Ellison’s Spiritual Health Questionnaire was selected as the criterion instrument.