Observational studies are a type of analytical study where researchers observe events without any interventions. In other words, the researcher does not influence the response variable or the experiment's outcome.

There are three types of observational studies – Prospective, retrospective, and cross-sectional.

Prospective Study

Prospective studies, also known as longitudinal or cohort studies, are carried out by collecting future data from groups sharing similar characteristics. One example of a prospective study would be assessing the effect of diet, exercise, and medication on heart disease among the residents of a specific city. Prospective studies are instrumental for medical researchers, especially in epidemiology. These studies allow scientists to observe the progression of a disease over time and compare the risk factors among subjects.

Retrospective Study

On the other hand, retrospective or case-control studies are conducted in the present but require researchers to collect data from the past. An example of such a study would be determining a relationship between tobacco smoke and chronic obstructive lung disease based on the smoking history of patients with chronic obstructive lung disease.

Cross-sectional Study

A cross-sectional study is one in which the data is collected and analyzed at a specific time. Evaluating the prevalence of cancer among people of different age groups, gender, social background, and geographical location is an example of a cross-sectional study.