Primary Studies include Experimental Studies & Observational Studies
For some types of medical research, experimental Randomized Controlled Trial studies (RCTs) are considered the primary research gold standard. Where it is not possible to do an experimental study like an RCT, an appropriate type of observational study (also known as a non randomized controlled trial) may be used to answer a research question.
Experimental Studies:
are primary studies where conditions are under the direct control of the investigator. They are specifically designed to test the efficacy of a preventive or therapeutic measure.
Randomized controlled trial (aka RCT or randomized trial):
An experiment in which individuals are randomly allocated to receive or not receive an experimental diagnostic, preventive, therapeutic or palliative procedure and are then followed to determine the effect of the intervention. Considered the gold standard for experimental research in clinical medicine. E.g. Parachute use to prevent death and major trauma when jumping from aircraft
Observational Studies:
describe study designs that are not randomized trials. Researchers in these studies do not intervene but rather observe the behaviour & risk factors of the study participants & record whether a disease or condition develops.
Case control study: a study in which patients with a specific condition (cases) are compared to patients who do not have the condition (control). The researcher looks
backward in time to look for factors or exposures that may be associated with the condition. The researcher may look at patient records or rely on patient recall for data.
E.g.
: Risk factors for pulmonary tuberculosis in Russia: case-control study
Cohort study (aka prospective or longitudinal study): an investigation that follows a large selected group following a treatment or with a specific condition & compares it with another selected group that does not have the condition or is not following the treatment. Both cohorts are followed
forward in time.
Example: a study that compares Doctors who smoke with Doctors who do not smoke to see if there is a relationship between dementia and smoking.
E.g.
Smoking and dementia in male British doctors: prospective study
Cross-sectional study: The observation of a defined population at a single point in time or during a specific interval. Exposure and outcome are determined simultaneously. This is a study that seeks to determine the "presence or absence of a disease and the presence or absence of exposure,
at a particular time."
Example: a study that extracts a subset (cross section) of data from a national census and then surveys that cross section of persons to determine whether they have been exposed to an event/condition.
E.g.
Factors associated with spousal physical violence in Albania: cross sectional study
