Definitions of Research Designs

Systematic Reviews & Meta-Analyses

• A systematic review critically assesses and evaluates all research that addresses a particular research question and presents a synthesized summary of the literature. The researchers use a systematic methodology to search and screen the literature on a particular topic. Meta-analyses use statistical methods to combine the results of individual studies and synthesize the findings.
• The quality of a systematic review is only as good as the quality of the studies that are included. When evaluating this type of study, you want to assess the methodology of the search strategy and screening of articles to include, and the assessment by the authors of the included studies.

Randomized Controlled Trials (RCT)

• A study design that randomly assigns participants to an experimental group (which receives the intervention) or a control group (which receives either a placebo or no intervention). The only expected difference between the two groups is the variable being studied.
• When critically appraising an RCT, you will evaluate elements of the study such as the allocation of participants, how similar the control group and the experimental group are, and the blinding of the participants and health care workers.

Cohort Studies

• A study type in which people who currently have a certain condition or receive a certain treatment are followed over time and compared with a group of people who are not affected by the condition or treatment.
• When critically appraising a cohort study, you will investigate how the cohort was recruited, if the exposure was accurately measured and bias was minimized, and if authors have identified and taken account of possible confounding factors.

Case Control Studies

• An observational study of people with a disease (or other outcome variable) of interest and a control, comparison, or reference group of people without the disease. The two groups of people are compared to determine what can be attributed to the disease or outcome variable.
• Much like a cohort study, when critically appraising a case series you will examine whether the authors have minimized bias and properly addressed any potential confounding factors.

Some study types are not named on the EBM Pyramid, but are important study designs for answering research questions:

Diagnostic Studies

• This type of research focuses on estimating the sensitivity and/or specificity of a particular diagnostic test, and compares the test to the standard diagnostic test.
• When critically appraising this type of study you will want to determine if the new test was compared with an appropriate standard test, if all patients received both the new test and the standard test, and whether the health care workers administering the tests were properly blinded to the results of the standard test.

Economic Evaluation

• This type of study compares the costs and outcomes of healthcare interventions.
• When critically appraising an economic evaluation, you will determine if there is evidence that the new intervention or program is effective, if the effects of the intervention were measured appropriately, and were the costs valued in a credible manner.

Qualitative Studies

• Qualitative research aims to identify what matters most to patients or populations and how their experience can be improved. In public health, this type of research allows researchers to explore social and behavioral issues and explore other social or human problems.
• Critical appraisal of a qualitative study will determine if there was a clear aim for the research, if the qualitative methodology and research design were appropriate for the aims, and if the data analysis was sufficiently rigorous.