1. Understanding real research 2.
Case control studies.

2. What can studies do? Describe the situation: Descriptive.
Explain the situation: Analytical.
Compare approaches: Experimental.

3. Study designs. Descriptive Cross-sectional, longitudinal. Analytic
Case-control studies.
Cohort studies.
Quasi-experimental
Natural experiments, policy interventions.
Experimental
Randomised controlled trial.

4. Study designs

5. Prevalence
Cross-sectional
Cause/
Aetiology
Cross-sectional;
Case-control;
Cohort.
Prognosis
Harm
Effectiveness
Randomised controlled trial.

6. Past Present Future Cross-sectional Case-control Cohort
From Altman. Practical Statistics for Medical Research, 1991.

7. Case control studies: Key features.
Retrospective, i.e. backward looking.
Relate an effect or outcome to a probable cause.
Individuals with disease (cases) compared to individuals without disease (controls).

8. Case control study.
From:

9. Advantages & disadvantages
Quicker than cohort studies
No measure of incidence
Relatively small study population required
Can only investigate one disease at a time & no temporal association
Good for rare diseases – can select all known cases
Retrospective, so data may be biased, e.g. poor records; memory recall
Case selection bias – must define cases very explicitly
Control selection bias
Matching controls to cases can be difficult
Can only determine the odds ratio, not relative risk

11. Appraising case control studies
Methodological approach:
Are cases and controls similar, except for exposure to the putative cause?
Is collection of retrospective data objective?
Is there evidence of “causation”?
Statistical reporting:
Type of data – influences statistical analysis.
Reporting of risk.