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AKU-KE | Introduction to Critical Appraisal Skills: Study Designs

Study designs

Identifying the study design is important in ensuring critical appraisal is carried out in the right manner as different study designs require different aspects of the study to be appraised.
The most common types of study designs are:
•    Qualitative studies:
Qualitative studies explore and understand people's beliefs, experiences, attitudes, behaviour and interactions. They generate non-numerical data. 

Examples of qualitative studies:

»    Document
»    Passive observation 
»    Participant observation 
»    In depth interview
»    Focus group

•    Quantitative studies
Quantitative studies generate numerical data. 
Examples of quantitative studies:

»    Randomized Controlled Trial (RCT) 
»    Systematic review
»    Case report 
»    Case series 
»    Case control study 
»    Cohort study

Spotting the Study Design
The type of study can generally be worked at by looking at three issues:
Q1. What was the aim of the study?

  • To simply describe a population (PO questions)    Descriptive 
  • To quantify the relationship between factors (PICO questions)   Analytic

Q2. If analytic, was the intervention randomly allocated?

  • Yes? ⇒ RCT 
  • No?  ⇒ Observational study

Q3. If observational, when were the outcomes determined?

  • Some time after the exposure or intervention?  ⇒ cohort study ('prospective study')
  • At the same time as the exposure or intervention?  ⇒ cross sectional study or survey
  • Before the exposure was determined?  ⇒ case-control study ('retrospective study' based on recall of the exposure)