Subgroup analysis
ARF
ARF
We conducted post hoc analyses to explore whether the effects of the age-related fertility information on the primary outcome, the ideal age at first childbirth, were heterogeneous by participants’ gender. At pretest, the average ideal age at first childbirth was significantly lower among female participants (mean = 29.7; SD = 1.94) than among male participants (mean = 31.1; SD = 2.43) (P < 0.001 for the test of difference between females and males). At posttest, the adjusted difference between the ARF group and the control group was -0.34 years (P = 0.001) in the female subgroup and -0.12 years (P = 0.548) in the male subgroup. However, post hoc sample size calculation indicates that our study groups were adequately powered for the female subgroup, but not adequately powered for the male subgroup. Statistical interaction tests also suggest that the differences in treatment effects between the two subgroups were not statistically significant (P = 0.298). Hence, we are unable to conclude whether the effects of the intervention differ between women and men (even though the magnitude of the effects was larger in the female subsample).