A new study published in the Archives of Pediatrics and Adolescent Medicine shows a positive correlation between counties in California, Oregon, and Washington with greater precipitation and a higher incidence of autism. While the results of this study are interesting, it needs to be put into proper context. Also of note, the authors had presented early results from this data previously.
Correlation is not Causation
This type of study is a correlational study, which means it asks whether or not there is a statistical correlation between two variables – in this case the rate of autism and the amount of precipitation. This type of data is extremely useful to medical science, but it has known limitations, which can be summarized by the statement that correlation is not causation.