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- Different than controlled experiment
- do not assign subjects to treatment or control groups. Some subjects have condition whose effects are being studied: this is the treatment group. the other subjects are the controls
- Smokers= treatment Group) (Non-smokers = Controlled)
- try to find-out how subject came into groups
- are the groups comparable? different?
- what factors are confounded with treatment
- what adjustments were made for confounding? were the sensible?
- Observational studies can establish association (one thing is linked to another)
- association may point out causation (if one group is exposed to chemicals they should be sicker than the other)
- association does not prove cause: (confounding)
- Observational studies can be misleading about cause and effect because of confounding
- Confounding is a third variable associated with exposure and disease.
- In observational studies a confounding factor can sometimes be for by comparing other groups which are relatively homogeneous with respect to the factor.
Control Groups Vs Observational
Questions to ask
- Ask questions
- Were there any control groups at all?
- if so were historical control are contempary used?
- how were the assigned to groups under the control of an investigator (controlled experiment) or out the control of an investigator (observational experiment)?
- If controlled were they assigned via (randomized controlled) or at the discretion of the investigator?
Weakness of Observational Studies
The great weakness is confounding: randomized experiments minimized this problem
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