In a study of prostate cancer mortality rates with dietary practices age-standardized prostate cancer mortality rates for 71 countries were obtained from the GLOBOCAN 2000 database, that has data on cancer incidence, mortality, and prevalence on most of the countries of the world. Per capita food consumption rates for each country were obtained from the FAOSTAT database for which country level data are collected annually. The results of this study showed a strong association between sugar consumption and prostate cancer mortality. This is an example of ... : (select one best answer) O cross-sectional study O case-control study O ecological study O retrospective cohort study O concurrent cohort study