Here's a search string to return Retrospective Studies in PubMed:
"Retrospective Studies"[Mesh] OR retrospective
You might want to consider including case-control studies, in which case you could use:
"Case-Control Studies"[Mesh] OR retrospective OR case-control OR "case control" OR "case controlled"
Sum it up: An observational study, retrospective studies look at what happened in the past, sometimes just to get percentages (e.g. this percentage of a specific population has a certain condition), and sometimes to see a correlation (e.g. this percentage of people in this population are smokers, and they have cancer at this rate compared to non-smokers who have cancer at that rate).
- case control studies are retrospective studies
Example in an elementary school classroom: If you were to ask the class "how many of you have ever broken a bone?" that is a retrospective study.
Examples from the literature:
Found in MeSH: under Epidemiologic Studies, either Case-Control or Cohort
if they want case-controlled studies as well. Case-controlled studies are often similar/same? as these.