Subject - Health

Understanding Study Designs

A study design is the blueprint for how research is conducted. Knowing the design helps you:

• Judge the strength and reliability of the evidence.
• Select the correct appraisal tool.
• Decide whether results are applicable to practice.

Main Types of Study Designs

1. Randomised Controlled Trial (RCT)

• Participants are randomly assigned to groups.
• One group receives the intervention; the other receives a placebo or standard care.
• Best for testing whether a treatment works because randomisation reduces bias.

2. Cohort Study

• Follows a group (cohort) over time.
• Compares those exposed to a factor with those not exposed and tracks outcomes.
• Can be prospective (looking forward) or retrospective (using past records).
• Good for identifying links between exposures and outcomes.

3. Case–Control Study

• Starts with people who have a condition (cases) and compares them to those without it (controls).
• Looks back in time for possible causes or risk factors.
• Useful for rare diseases; more prone to bias due to reliance on memory and records.

4. Cross-Sectional Study

• Observes a defined population at a single point in time or time interval.
• Measures exposure and outcome simultaneously.
• Useful for describing patterns or associations, not cause and effect.

5. Systematic Review and Meta-Analysis

• Systematic Review: Identifies, appraises, and synthesises all relevant studies on a specific question using explicit methods.
• Meta-Analysis: Uses quantitative methods to combine results across studies into an overall estimate.

6. Qualitative Research

• Explores experiences, perceptions, and meanings rather than numerical data.
• Uses interviews, focus groups, and observations.
• Meta-synthesis: Systematically synthesises findings across multiple qualitative studies.

7. Case Report / Case Series

• Describes one or more patients with a specific outcome or presentation.
• No control group; useful for new or unusual cases but provides weaker evidence.

8. Diagnostic Accuracy Study (Prospective, Blind Comparison to a Gold Standard)

• Evaluates a new diagnostic test against the best available gold standard.
• Both tests are administered to all participants, and interpretation is blinded.
• Reports measures such as sensitivity and specificity.

Summary Table (At a Glance)

Key Definitions

• Case Report / Case Series: Descriptive reports on one or more patients; no control group.
• Case–Control Study: Compares people with an outcome (cases) to those without (controls) and looks back for exposures.
• Cohort Study: Compares exposed and unexposed groups and follows them for outcomes.
• Randomised Controlled Trial: Randomly allocates participants to intervention or control and follows outcomes.
• Systematic Review: Comprehensive, critical summary of the literature using explicit methods.
• Meta-Analysis: Quantitative synthesis of results from multiple studies.
• Meta-Synthesis: Systematic synthesis across qualitative studies.
• Cross-Sectional Study: Measures exposure and outcome at the same time in a defined population.
• Diagnostic Accuracy Study: Compares a new test to a gold standard to determine accuracy (e.g., sensitivity and specificity).

What is Critical Appraisal?

Critical appraisal is the careful and systematic evaluation of research studies to decide whether the evidence they provide is reliable, relevant, and applicable to practice. It helps you determine:

• Is the study credible and well-designed?
• Are the results valid and important?
• Can the findings be applied to my patient or population?

If a study does not meet these standards, it may not be appropriate to use its findings in clinical decision-making.

Why is Critical Appraisal Important?

• Ensures that clinical practice is based on strong, reliable evidence rather than weak or biased studies.
• Helps identify the strengths, weaknesses, and potential bias in research.
• Supports safe, effective, and evidence-informed healthcare practice.
• In evidence-based practice (EBP), only the best available evidence should guide care decisions.

What Are Critical Appraisal Tools?

Critical appraisal tools are structured checklists or worksheets that guide you in evaluating a study’s:

• Design and methods
• Results and conclusions
• Relevance and trustworthiness

These tools help you judge whether the evidence is strong enough to inform clinical or professional decisions.

Which Tool Should I Use?

Commonly Used Critical Appraisal Tools

CASP (Critical Appraisal Skills Programme)

• Student-friendly and easy to use.
• Includes checklists for RCTs, Cohort, Case–Control, Qualitative, and Systematic Reviews.
• View CASP Checklists

Joanna Briggs Institute (JBI)

• More detailed checklists covering a wide range of study types.
• Provides downloadable appraisal tools and guidance.
• View JBI Tools

Centre for Evidence-Based Medicine (CEBM)

• Step-by-step worksheets for systematic reviews, diagnostics, prognosis, RCTs, and qualitative studies.
• View CEBM Worksheets

Scottish Intercollegiate Guidelines Network (SIGN)

• Methodology checklists for systematic reviews, RCTs, cohort, case-control, and diagnostic studies.
• View SIGN Checklists

BestBETs

• Offers 13 critical appraisal worksheets covering a range of study designs, including harm, diagnosis, prognosis, and reviews.
• View BestBETs Worksheets

EQUATOR Network

• Provides reporting guidelines (e.g., CONSORT, STROBE, PRISMA) to improve the quality of research publications.
• Useful for understanding how well a study is reported, not for appraisal itself.
• Visit EQUATOR Network

In Summary

Critical appraisal helps you:

• Determine the quality and trustworthiness of research evidence.
• Make confident, evidence-informed clinical decisions.
• Support safe and effective nursing and health science practice.

Adapted from CASP, JBI, CEBM, SIGN, and Duke Libraries’ Intro to Evidence-Based Practice.