2.2. Sample Size Estimation
A 2-by-2 repeated measures design was adopted, with two groups of participants being measured at two different time points. The primary goal of the study was to compare the change in the intervention group to the change in the control group over time. Sample sizes were calculated for all study variables, including vitamin A, vitamin D, zinc, and hemoglobin. The maximum sample size was determined for hemoglobin; thus, the sample size estimation for this investigation was based on hemoglobin levels. A sample size of 47 in the intervention group and 47 in the control group achieved 81% power to detect a difference in mean changes of 0.61 g/dL with an SD of 1 at the first time point, an SD of 0.88 at the second time point, and a correlation of 0.4 between measurement pairs. With a 20% attrition rate, the sample size was extended to 58 in each group. The significance level (alpha) for a two-sided, two-sample t-test was set at 0.05 [