More reading - lots of big strange words and some statistics, but read slowly and carefully it does explain to us how valuable - or otherwise - those observational studies really are. And the end result is - not awfully because you can take the same results and the result will be very different depending on how the statistics app analyses them!
medscape.com/viewarticle/re...
It has been said for years that the most important person in the research group is the stats advisor - because you can get the answer you want by choosing how you analyse the results ...