Substituting the values in the formula thus defined the error (a)of 5% (¼1.96) and the statistical power (1 b) of 90% (¼1.28). The calculated sample size was 442.7 y 443. Because this study explored many variables, therefore, the sample size [14] when np was the adjusted sample size, and n1 was the calculated sample size was made using the formula for simple logistic regression analysis. R2 was the coefficient of multiple logistic regression, and for this study was set at 50% (R2 ¼ 0.50). The calculated sample size using the formula was 886 individuals.