11. Analytical epidemiological studies: case control studies, types, design, conducting, advantages, disadvantages, potential errors

Analytical epidemiological studies. Case control studies - types, design, conducting, advantages and disadvantages, potential errors.

Analytical epidemiological studies:

Look at individual within the population —> the inference is not individuals but to the population from which they are selected

Comprise 2 distinct types of studies:

1. case-control study:
2. 2.

1st approach to test causal hypothesis —> are comparison studies —> cases & controls must be comparable but respect factors that can’t be influenced, i.e. age, sex

Focus is on disease / other health problem that has already developed

Features of study= exposure & outcome have occurred before the start, it proceeds backwards from effect to cause, it uses control or comparison group to support / refute an inference

Involves 2 populations= cases, controls

Design of study (i.e.): research hypotheses that cigarette smoking causes lung cancer —> investigation begins by assembling a group of lung cancer cases (a+c) and a group of suitable matched controls (b+d) —> then: past history of groups for the presence or absence of risk factor which is suspected to be related to the occurrence of some disease

4 steps:

1. Selection of steps and controls: selection of cases from hospitals or general population, controls must be free from disease under study —> must be as similar to cases as possible
2. Matching: consideration is to ensure comparability between cases & controls —> process by which they select controls in a way that they are similar to cases with regard to variables which are known to influence the outcome of disease & could distort or confound result
3. Measurement of exposure: information obtained by interviews, questionnaires or studying past records of cases i.e. hospital records
4. Analysis- estimation of risk: estimation of disease risk associated with exposure is obtained by Relative Risk (RR) = ration between the incidence of disease among exposed persons & incidence among non-exposed —> odds ratio = measure of strength of the association between risk factor & outcome

Advantages:

enable us to study rare health outcomes

are generally quicker, cheaper and easier to conduct

enable us to study more than one risk factors at the same time

are suitable for diseases with long latent period

Disadvantages:

are not suitable for studying rare exposition

greater potential for bias

non possible to measure incidence rates in the groups of cases and controls

non possible to measure the absolute and the relative risks

2. cohort study