Harvard study involved data from more that 140,000 people.

This quote from the article was quite interesting as many housing developments are built on what was once farmland.

Dr. Ascherio noted, however, that farmers and non-farmers (such as gardeners who regularly used pesticides) had similar levels of risk so it appears to be pesticides that increase risk, not other aspects of farming.

Pesticides linked to increased risk of Parkinson's – globeandmail.com

Pesitcides Linked to Parkinson's in Grim New Studies – lime.com

[thanks, Jeff]