Prospective cohort study

[2] After baseline information is collected, subjects in a prospective cohort study are then followed "longitudinally," i.e., over a period of time, usually for years, to determine if and when they become diseased and whether their exposure status changes outcomes.

In this way, investigators can eventually use the data to answer many questions about the associations between "risk factors" and disease outcomes.

For example, one could identify smokers and non-smokers at baseline and compare their subsequent incidence of developing heart disease.

Alternatively, one could group subjects based on their body mass index (BMI) and compare their risk of developing heart disease or cancer.

[6] STROBE also recommends that whenever authors use these words, they specify which definition they use, including a detailed description of how and when data collection took place.