A<unk>  (from Latin retrospectare, "look back"), generally, is a look back at events that took place, or works that were produced, in the past. As a noun,<unk>  has specific meanings in medicine, software development, popular culture and the arts. It is applied as an adjective, synonymous with the term retroactive, to laws, standards, and awards.
Retrospective
Natural history group
N of 1 trial
Case series
Population study
Multiple baseline design
Cohort study
Parallel study