important to understand - Relative risk cannot be calculated for retrospective studies ODDS RATIO can be calculated for prospective and retrospective

Observational studies include

cross-sectional

Cohort

Case studies / Case series (plural)

Cross-sectional studies

Retrospective observational study type

RR cannot be calculated (due to retrospective)

Odds ratio can be calculated

cross-sectional studies looks at a specific population during a specific time period, the population only must meet the criteria of the trial itself they are not selected on the exposure or outcome status (eg must have been exposed to asbestos or must have cancer so we can look at risk factors or outcomes of this - this is in case studies not cross sec) such as in case studies.

cross-sectional studies may be something like.. we want to measure disease A in village B

so to meet the criteria you. must live in village B.

Cross-sectional studies are useful for determining possible relationships which can then be looked at in more detail by other studies

Cohort studies

Prospective observational study type

RR can be calculated (due to prospective)