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Research Cycle: Study Designs

A step by step guide to the research process

Tips and Tricks

  • Which type of Study design best fits my research question?
  • Below is the Levels of Evidence pyramid, that ranks the validity of evidence and the type of studies that are most common.
  • The higher the study design is listed on the pyramid, the more rigorous the research methods and unbiased (hopefully).

  • Systematic Reviews and Randomised Controlled Trials (RCT's) are the most common study design.
  • Refer to the table below to identify your question type, Intervention, diagnosis and the associated study design.
Question
Best Study Design
Description
Intervention Randomised Controlled Trial (RCT) Subjects are randomly allocated to treatment or control groups and outcomes assessed. How to select treatments to offer patients that do more good than harm
Aetioloy  RCT Aetiology are similar to intervention questions, so an RCT is the ideal study type. How to identify causes for disease.
  Cohort Study Outcomes are compared for matched groups with and without exposure or risk factor (prospective study)
  Case-control study Subjects with and without outcome of interest are compared for previous exposure or risk factor (retrospective study)
Diagnosis Cross-section study with random or consecutive sample. How to select and interpret diagnostic tests
Prognosis Cohort study How to estimate the patient's likely course over time and anticipate likely complications of disease.

 

 

Study Designs - Detailed Descriptions

Below is more detailed explanation of the different types of study designs.

Meta-analysis

A quantitative method of combining the results of independent studies, which are drawn from the published literature, and synthesizing summaries and conclusions.

Systematic Review

A review which endeavours to consider all published and unpublished material on a specific question.  Studies that are judged methodologically sound are then combined quantitatively or qualitatively depending on their similarity.

Randomised Controlled Trial (RCT)

A  clinical trial involving one or more new treatments and at least one control treatment with specified outcome measures for evaluating the intervention.  The treatment may be a drug, device, or procedure. Controls are either placebo or an active treatment that is currently considered the "gold standard". 

Cohort Study

In cohort studies, groups of individuals, who are initially free of disease, are classified according to exposure or non-exposure to a risk factor and followed over time to determine the incidence of an outcome of interest.  In a prospective cohort study, the exposure information for the study subjects is collected at the start of the study and the new cases of disease are identified from that point on.  In a retrospective cohort study, the exposure status was measured in the past and disease identification has already begun. 

Case-control Study

Studies that start by identifying persons with and without a disease of interest (cases and controls, respectively) and then look back in time to find differences in exposure to risk factors. 

Cross-sectional Study

Studies in which the presence or absence of disease or other health-related variables are determined in each member of a population at one particular time. 

Recommended Readings

If you are working on a research project, these titles provide more detailed readings into study designs.

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