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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 . Bias. Bias means “different” 3 types of bias: Selection Bias Information Bias Confounding. Selection Bias Examples.

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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. Bias • Bias means “different” • 3 types of bias: • Selection Bias • Information Bias • Confounding

  3. Selection BiasExamples • Patients referred for specialist care are different from those in the community • Migration bias. People with chronic lung disease tend to move out of urban areas; those with psychiatric problems seek the anonymity of cities • High dropout rates. Those who drop out of a study tend to be different from those continuing

  4. Information BiasExamples • Response Bias occurs when subjects give inaccurate responses. • Measurement Bias occurs when instruments are faulty • Observer error • A process tends to show improvement when being observed. (Hawthorne Effect)

  5. Strategies for Avoiding Bias • Have clear and precise definitions (e.g. for cases; controls;exposure;criteria for inclusion/exclusion) • “Blinding” where appropriate • Reduce measurement error by ‘quality control” • careful check of study design; choice of subjects; ascertainment of disease and exposure;planning of questionnaires; methods of data collection.

  6. Confounders • Confounders act by being associated with both a risk factor and outcome in a way that makes the two seem related. Poor Maternal Nutrition Low Birth Weight Low Socioeconomic Class

  7. Dealing with Confounders - 1 • Think about possible confounders at the design stage, and gather data on all possible confounders. • A quick test about a possible confounder is to check whether it is unevenly distributed between study and comparison groups. • Suspect confounding if the odds ratio gets altered after adjusting for another factor.

  8. Method of Checking for a Possible Confounder • First calculate Odds Ratio for the exposure variable. • Next calculate odds ratio for different strata of the confounding variable • If the odds ratios are not materially different then there is no confounding.

  9. Strategies for dealing with Confounding • Design Stage • Strict inclusion criteria • Matching • Randomization • Analysis Stage • Do analysis by adjusting for several strata of the confounding variable • Multiple regression analysis

  10. Validity • Are the conclusions true? • Common threats to validity • Selection bias • Measurement bias • Differential loss of subjects • Confounders • Unexpected events • Hawthorne effect

  11. Strategies for ensuring validity • Have a control group. Helps against confounding, unexpected events, Hawthorne effect. • Random assignment of subjects to different groups. • Before / After measurements. • Carefully prepared research designs. • Quality control of equipment • Knowledge of environmental events especially if the study is of long duration. • Unobtrusive methods of observation.

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