EAB: Cohort Study and Case Control Study Flashcards
What do epidemiological /cohort studies associate?
epidemiological studies associate risk factors with health outcomes
What are 6 example risk factors?
- Lifestyle eg diet, smoking
- Physical environment eg radiation
- Social environment eg marital status
- Genetic eg BRCA gene
- Early life eg birth weight
- Medical interventions
What are 3 health outcomes?
- Mortality (eg death, survival)
- Morbidity (eg onset of disease)
- Health status (eg symptom severity, quality of life)
How does a cohort study differ to a case control study?
- Cohort study starts with the risk factor and follow up to see who develops the disease or not.
- Case control study starts with the disease.
Describe a cohort study design.
- subjects usually free of disease
- groups defined according to risk factor exposure status followed up over time to evaluate health outcome
- compare incidence of disease in exposed and unexposed
What are 3 types of bias are found in cohort studies?
- Selection bias:
- selection of participants:- sampling frame
- response rate
- loss to follow-up
- Information bias:
- measurement error/bias:- risk factor measurement
- outcome measurement
- Confounding
What is a confounder?
A confounder is a factor associated BOTH with the exposure under study AND independently with the disease.
What are the 4 methods to address confounding?
- Restriction
- Matching
- Stratification
- Regression adjustment
What are case-control studies?
Case-control study compares risk factor exposure in cases and controls
What are 3 methods for control selection?
- Population register
- Neighbour
- Clinic or hospital based
Why may you match the control group and the group with the disease?
- Usually used to make allowance for confounders more efficient eg age, sex
- Can reduce bias
- Must be allowed for in analysis
What are the disadvantages of matching?
- Matching variable cannot be evaluated as risk factor
- ’Overmatching’
What are the 2 types of bias that are found in case-control studies?
- Selection bias
- selection of cases
- selection of controls - Information bias
- exposure ascertained after outcome status is
known
- often retrospective based on recall
Compare case-control and cohort studies.
what are 7 factors that suggest causation?
- Strength of association (high relative risk or odds ratio)
- Dose-response relationship (more exposure, greater risk)
- Temporality (cause before effect)
- Consistency (multiple studies confirm association)
- Experimental evidence (e.g. animal experiments, randomised controlled trials, natural experiments)
- Specificity (one cause one effect, though not always as smoking causes many diseases)
- Plausibility (a plausible mechanism exists)
when looking at cohort studies, we draw up a 2 by 2 table measuring the risk against the factor, draw out this table
what is the odds ratio equation
