Question

In the July issue of Archives of Neurology, researchers reported studying the smoking habits of 12000 people (3000 with Parkinson's disease and 9000 healthy people). They found that those who had smoked the most (the equivalent of a pack a day for 60 years) had the lowest risk of getting Parkinson's disease.Was this anecdotal evidence, an observational study or an experiment?

(Im leaning towards observational study but I don't know)