Indicate how the bias would affect the measure of association. Would it be under estimated, or over estimated or unchanged.
Persons diagnosed as HIV positive or negative were interviewed about their number of lifetime sexual partners. The interview occurred after they were told their HIV status.
2. A cohort study looked at the association of exposure to PCBs in the workplace and the occurrence of cancer over 20 years. At the 10-year follow up, 15% of the original participants could not be located to assess their disease status.
3. In a clinical trial of a new drug, the intervention group reviewed the medicine and outcomes were assessed by a doctor working for the pharmaceutical company. The placebo group received the placebo and outcomes were assessed by a doctor from the local community hospital.
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