Clinical Study Types - for Librarians

• PubMed's MeSH term: Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons.  Year introduced: 1967(1965)      
• Cancer.gov: A study that compares two groups of people: those with the disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls). Researchers study the medical and lifestyle histories of the people in each group to learn what factors may be associated with the disease or condition. For example, one group may have been exposed to a particular substance that the other was not. Also called case-control study
• Stasticshowto.com: A retrospective study is an observational study that enrolls participants who already have a disease or condition. In other words, all cases have already happened before the study begins. Researchers then look back in time, using questionnaires, medical records and other methods; Basically, you just dig into the data and see what you find. The goal is to find out what potential risk factors or other associations and relationships the group has in common. The opposite of a retrospective study is a prospective study where participants are enrolled before any of them have the disease or outcome being investigated. 

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: 

• Patient reported outcome of 33 operatively treated talar fractures
• Association between body mass index and short-term mortality in patients with intra-abdominal infections: a retrospective, single-centre cohort study using the Medical Information Mart for Intensive Care database.

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.