I ran a pilot study, an 89-item survey instrument in which the last 6 are summed into an intent-to-stay index. The mean and standard deviation of the index is useful for calculating a sample size (Is this assumption correct?).

n = (s)^2 * (t)^2 / (d)^2, where s is standard deviation, t is critical value of 1.96, and d is (.1*mean)

From pilot study

standard deviation of index = 5.839

Mean = 20.33

n = (5.839)^2 * (1.96)^2 / (.1 * 20.33)^2

n = 32

My questions are:

1. Do I only use the dependent variable (intent to stay) index to calculate the mean or do I do the same calculations for the independent variables too (emotional, appraisal, informational, and instrumental support)?

Thank you for your help and guidance.