Sample size
The primary outcome of the MILC study was any breast milk feeding at 6 months. We wanted to be able to detect
a difference in the prevalence of breast milk feeding in relation to the primary exposure variable, that is, that
the infant was ‘fed directly at the breast only’ from birth to the time of recruitment 24–48 h after birth, and chose 10% as a meaningful clinical difference. To calculate the sample size, the 2009 Victorian State average of any breast milk feeding at 6 months postpartum was used. To detect a 10% difference from 46% (the Victorian data estimate of feeding any breast milk at 6 months34)