Sample Size, Randomization, and Blinding
We estimated that 356 parents (178 in each group) were needed, considering our hypothesis that using the KhunLook app could decrease the proportion of parents with low to fair HL from 83.2% by 15% when compared with the MCHH with a power of 80% and a significance level of 5%. Considering possible loss to follow-up, we recruited just over 400 parents. We used a computer-based block-of-4 randomization list to allocate parents at a 1:1 ratio to either the control group or the intervention group. Allocation concealment was ensured using opaque envelopes (Piangjit Tharnprisan), which was opened by the research assistant (Marisa Klangkhumpa) after completion of informed consent whereby the parent was informed of their allocation group. The parents were not blinded to the allocation due to the nature of the intervention.