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Mother and Child Health: Research Methods

Mother and Child Health: Research Methods. G.J.Ebrahim Editor Journal of Tropical Pediatrics, Oxford University Press . Case-Control Studies. Exposure. Yes. Cases. No. Yes. Controls. No. Population at risk. Steps in Designing Case-Control Studies.

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Mother and Child Health: Research Methods

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  1. Mother and Child Health: Research Methods G.J.Ebrahim Editor Journal of Tropical Pediatrics, Oxford University Press.

  2. Case-Control Studies Exposure Yes Cases No Yes Controls No Population at risk

  3. Steps in Designing Case-Control Studies • Selection of cases. Precise definition of ‘case’. Inclusion / Exclusion criteria. Are cases to be ‘incident’ or ‘prevalent’? How are cases to be identified? How recruited? • Selection of Controls. Source ( hospital patients without disease; neighbourhood controls; random sample of population; sibs). Inclusion / exclusion criteria. Match to cases? • Collection of information. Identify risk factor of interest. Method of collection of information ( questionnaire; medical records; employment records). Same procedure to be used for cases and controls. Interviewer should be unaware who is a case and who a control.

  4. Select new cases (i.e.incident) as they come up. Controls are selected from those in the same setting at the same time. Select existing cases (prevalent) from a defined population. From the same population a larger number of controls are identified. Two Methods of Selection The Incident type of case-control study is stronger because diagnosis of cases and ascertainment of exposure is being done by the researcher.

  5. Calculation of risk Cases Non-cases Exposed A B C D Not Exposed Odds Ratio = A×D ÷ B× C

  6. Matched case - Control Studies cases All cases or random sample cases Controls Random sample of non-cases Non-cases cases All cases or random sample cases Controls Matched controls Non-cases

  7. Relatively cheap compared to cohort studies Relatively quick Useful for study of rare diseases. No ethical problems Useful for diseases with long latent period. Estimate of disease incidence cannot be done At times difficult to measure exposure accurately Open to selection bias. Difficult to interpret. Advantages and Disadvantages of case-control studies. Advantages Disadvantages

  8. Points to be careful About • Confounders .Groups are self allocated and may have other risk factors with different distribution • Selection bias. Controls should be a representative sample of the same population where cases came from. • Recall bias. We ask about exposure after the disease has been diagnosed. • Interviewer bias. Best dealt with by “blinding” to hypothesis and whether subject is case or control. Also use same interviewer for cases and controls, and verify responses.

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