Observational Studies

In an observational study, a researcher observes, measures and records characteristics of interest of part of a population. It's easy to think that an observational study only takes place when a researcher is watching something happen in front of him/her. But that's not the only way we can observe.

Here are three ways observational studies can take place:

Cross Sectional Study: Data is observed, measured and collected at one point in time. For example, a researcher observes how many people stop to buy concessions at a movie theater.

Retrospective Study: Data is collected from the past by going back in time (through examination of records, interviews, receipts etc.) For example, a researcher observes how many people stopped to buy concessions at a movie theater in the last month by reviewing receipts stored on the cash registers. 

Prospective Study: Data is collected in the future from groups (called cohorts) sharing common factors. For example, a researcher may follow the spending habits of a group of people who frequent the movie theater to see if they will continue buying concessions in the future.