Much of what I do in my job is think about whether relationships we see in data are causal, as opposed to just reflecting correlations. It's exactly these issues which come up in evaluating studies in public health.
The basic idea that incentives can be used to motivate behavior is a powerful one. It works for employees, and it has a clear place in parenting, as anyone who has tried to potty-train a recalcitrant toddler with sticker rewards knows.
Even if you are planning a birth with an epidural, the evidence suggests that a doula can help make things go much more smoothly.
All's fair in love and purchasing.
Even though it is the case that poverty is linked to AIDS, in the sense that Africa is poor and they have a lot of AIDS, it's not necessarily the case that improving poverty - at least in the short run, that improving exports and improving development - it's not necessarily the case that that's going to lead to a decline in HIV prevalence.
Talking to women about birth can be polarizing.