Study design and sampling procedure

This was a community-based cross sectional study nested in a cluster-randomized trial that considered the same study population (pregnant women). The cluster randomized trial was on the effectiveness of an integrated intervention consisting of pregnancy buddies, mobile phone messages, and mama kits in increasing facility-based births. Sample size estimation was done using the Kish Leslie formula for cross sectional studies [13] and a 10% adjustment for non-response was made to come up with 423 respondents.

Where N = sample size estimate of pregnant women.

P = assumed true population prevalence of Hepatitis B screening services (50%).

Z_α = Standard normal deviate at 95% confidence interval corresponding to 1.96.

δ = Absolute error between the estimated and true population prevalence of Hepatitis B screening, (5%) at 95% CI.

Consecutive sampling method was used whereby every woman known to be pregnant within every village in the two sub-counties was approached and those who were eligible and consented to participate in the study were included until a sufficient sample size was accrued.

Though not a probability sampling method, it allows one to select all the accessible population in an area during the study period. This method is recommended for RCTs including the one in which our study was nested.