I haven't stated myself very clearly it seems. I was trying to say that it seems to me that in books like the one the OP mentioned, the author will look at 5 different studies of things that might raise IQ and then claim that if you do all 5 then you will get cumulative increases in IQ.
I question the validity of some of those studies, but I also very much doubt that you can say you can get x points for breastfeeding, another x points for a prepared environment and a further x points for a chemical free house. Even assuming the studies are sound, chances are that the same subjects who are extended breastfeeders might also be the low chemical householders and the prepared environment people and their kids higher IQ may be genetic. You could participate in all three studies and show that your child had an extra 5 points in each study - but your child is not 15 points higher for having done the three studies. Until someone comes up with a sound study of combined factors, if that is even possible, then I am very dubious of lists of things you can do for combined positive outcomes (even if I believe the individual studies, which in many cases I am not sure that I do).
I probably didn't explain that any better the second time.
