Sample size estimation
A previous study of pregnant women reported a mean IIFAS-J score of 62 for those who intended to breastfeed exclusively. We aimed to increase the IIFAS-J score by 3 points by using benefit language to present the latest infant feeding information. We expected that use of risk language to present the same information would not have an equivalent effect. Specifically, we assumed that the control group would have a mean score of 62 at both the pre-test and post-test and designed the intervention for Group 1 to increase the mean score from 62 to 65 (SD 5). To detect a difference in pre-test score between Group 1 and the control with 80% power and a two-sided alpha of 5%, we estimated that a minimum sample size of 44 for each group would be necessary (