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Flashcards in Epidemiological study design Deck (12):

Give 6 types of study design

Cohort study, case-control, intervention, ecological, cross-sectional


describe the design of a cohort study

An observational study

Longitudinal study in similar groups but with different risk factors/treatments

Follow up over time (constantly checking in)

(in contrast to case-control, the outcome has not occurred yet)


Describe case-control studies

An observational study looking at the cause of a disease. Compares similar participants w/ disease and those without (controls). Looks RETROSPECTIVELY for exposure/cause (potential RF data is collected - e.g. questionnaires)

The outcome has already occurred at the time of investigation

important idea: looks backwards in time


describe ecological studies

Observational study of a disease or outcome and exposure of interest are measured in a number of populations/groups (e.g. between electoral wards or different hospitals)


describe a cross-sectional study

Observational study collecting data from a population at a specific point in time (no follow-up) - i.e. a snapshot of a population

Example: the census (conducted every 10 years) --> other examples include prevalence at a specific time (e.g. number of smokers in a GP practice)


What is odds ratio?

Can be used in case control study


describe an RCT

Similar participants are randomly assigned to an intervention or control group to study effect of intervention


What are the advantages and disadvantages of an RCT?

- Low risk of bias and confounding
- Comparative
- randomised
- blind - reduces possibility of information bias

- High group out rate
- Ethical issues
- Time consuming and expensive
- prior knowledge required


What are the advantages and disadvantages of an ecological study?

Advantages: can lookout geographical correlations, good for generating a hypothesis

- subject to bias + confounding


What are the advantages and disadvantages of a cohort study?

- Can follow up rare exposure
- Allows to identify risk factors
- Data on confounders collected prospectively

- Large sample size required
- Impractical for rare diseases
- Expensive
- People drop out


What are the advantages and disadvantages of a case control study?

- Quick
- Good for rare outcomes

- Difficult finding appropriately matched controls
- Prone to selection and information bias
- Reverse causality (as the outcome interest has already occurred)

n.b. all the observational studies (case control, ecological, cohort, cross-sectional) are subject to bias and confounding


What are the advantages and disadvantages of a cross-sectional study?

- Large sample size
- Provides data on prevalence of risk factors and disease
- Quick to carry out
- Repeated studies show changes over time

- Risk of reverse causality – which came first?
- Less likely to include those who recover quickly or short recovery
- Not useful for rare outcomes
- subject to bias + confounding
- Temporality: impossible to be certain whether an outcome developed before or after the exposure concerned