Researchers have begun to hypothesize that pesticide exposure is linked to risk of developing pancreatic cancer. In order to collect preliminary data on a potential association, investigators decide to look at rates of pesticide exposure among 60 countries and rates of pancreatic cancer. Pesticide exposure was categorized as high, moderate, and low. Their results showed a strong correlation between high pesticide exposure and the development of pancreatic cancer. The investigators concluded that more research would need to be done before definitively linking pesticide exposure to the risk of pancreatic cancer. Pancreatic cancer is a rare disease.

On what basis did you determine which type of study this represents? Include all of the following: initial classification of study subjects; prospective, retrospective, or concurrent; unit of observation; and the number of observations (i. e. the number of data collection points by the investigator).