[ocschwar]

If you have access to statistics for the general population, you can forego the control group, I would think. But that requires doing the study in a country with a well run health care system and properly regulated medical records so that you can get these stats without privacy issues.

(Glances in Denmark's general direction.. )

[drjasonharrison]

You can also use Canada, with the exception of access to medical records, to minimize all of the differences between populations in the USA and the control group.

Denmark has a very different vaccination schedule because they have exposure to many fewer "childhood diseases." Might seem like a small difference given the availability of 'properly regulate medical records without privacy issues" but these sorts of differences add up.