The RCT doesn’t sound properly randomized if people were deciding themselves whether to listen to the advice? Perhaps people with higher IQ listen to the intervention better. And then we just see the genetic correlation.
As I understand it, the point of “intention to treat” RCTs is that there will be roughly as many people with high IQ in both groups, since they’re picked at random. People who get the advice but don’t listen aren’t moved to the “didn’t get advice” group.
So what the study measures is “On average, how much of an effect will a doctor telling you to breastfeed have on you?”. The results are more noisy, but less vulnerable (or even immune?) to confounders.
The RCT doesn’t sound properly randomized if people were deciding themselves whether to listen to the advice? Perhaps people with higher IQ listen to the intervention better. And then we just see the genetic correlation.
As I understand it, the point of “intention to treat” RCTs is that there will be roughly as many people with high IQ in both groups, since they’re picked at random. People who get the advice but don’t listen aren’t moved to the “didn’t get advice” group.
So what the study measures is “On average, how much of an effect will a doctor telling you to breastfeed have on you?”. The results are more noisy, but less vulnerable (or even immune?) to confounders.