Sample size and sampling

Stata V.14 software was used to calculate the sample size for this study using the menu option for determining the difference between two sample means with the assumption of: an anticipated mean count of mistreatment experiences women face in facility-based childbirth (pre-intervention) of 4.91, taken from a study conducted in Addis Ababa²⁶; an anticipated mean count of mistreatment experiences women face in facility-based childbirth (post-intervention) of 3.96 (mean difference of 0.95); statistical power of 90%; an allocation ratio of 1:1 between the pre-intervention and post-intervention groups; 0.05 level of significance; and 10% non-response rate. Additionally, women receiving care in the same hospital are more likely to receive comparable care during childbirth, so the sample size was adjusted for clustering by assuming a clustering effect of 2. With these assumptions, the minimum required sample size was calculated to be 378 (189 in the pre-intervention group and 189 in the post-intervention group). Eventually, 392 women were invited and 388 women were surveyed (190 in the pre-intervention and 198 in the post-intervention) making the response rate 98.9%; rushing to go home and lack of interest to participate were the reasons for non-participation. Allocation of samples to the three hospitals was made proportionately depending on the number of women who gave birth in the hospitals in the last quarter of 2017 for the pre-intervention survey, and the second quarter of 2018 for the post-intervention survey. Accordingly, 172 (87 pre-intervention, 85 post-intervention) women were surveyed from Adare hospital, whereas 86 (46 pre-intervention, 40 post-intervention) and 130 (65 pre-intervention, 65 post-intervention) were from Leku and Yirgalem hospitals, respectively. Eligible women were enrolled into the study consecutively until the required sample size was met.