LECTURE 02 2011

LECTURE 02 2011 - General Methods of Investigation 1 Chance...

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General Methods of Investigation 1. Chance observations 2. Case histories individual cases case series 3. Uncontrolled trials of an intervention 4. Cross-sectional (naturalistic) studies 5. Case-control studies 6. Prospective follow-up studies 7. Randomized clinical trial No planned concurrent comparison group
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Examples of Case-Control Studies 1. Multi-Center study of SIDS 2. Vaccine efficacy 3. Coffee drinking and CHD 4. Soluble biomarkers and all-cause mortality (nested case- control study)
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Example Hennekens et al. Coffee drinking and death due to coronary heart disease. NEJM 294:633-36, 1976. Purpose: To investigate the relation between coffee drinking and death due to CHD.
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Design: Individually matched case- control study Cases: Married, white men, aged 30-70 who died from CHD within 24 hours of symptom onset according to death certificate Controls: Age, sex, neighborhood matched Agent: Coffee consumption as assessed by interview with wife 2-8 weeks after death Consumption 3 months prior to
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Case-Control Study Hennekens et al. Coffee drinking and death due to coronary heart disease. NEJM , 1976. 1+ cups/day CHD Cases Neighborhood Controls 500 485 985 Prevalence of coffee drinking among cases = 500 / 649 = 77% Prevalence of coffee drinking among controls = 485 / 649 = 75% None 149 164 313 649 649 1,298
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Matched Analysis for Coffee Study 1+ cups/day 1+ cups/day None 359 126 485 Odds Ratio (OR) = = 1.12 None 141 23 164 500 149 649 Cases 141 126 ^ Controls
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Other Considerations in Interpreting Findings from Observational Studies Bias (def.) A systematic error usually introduced by investigator and/or patient which leads to incorrect estimates of the association between a risk factor and a disease endpoint. Case and control selection and recall bias are common problems in case-control studies
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Possible Sources of Bias in Coffee Case-Control Study 1. Identification of cases and controls 2. Interviewer 3. Wife’s report or memory of spouse’s coffee consumption
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Nested Case-Control Study: SMART Study Nested Case-Control Study: SMART Study Baseline plasma samples were identified for patients who died (85 patients) and for two matched controls for each death (170 patients). Matching was on country, age (+/- 5years), gender and approximate date of randomization (+/- 3 months). Conditional logistic for matched studies used to estimate odds ratios (OR) for mortality with participants in lowest quartile as reference. Adjusted OR consider covariates corresponding to age, race, ART, HIV RNA, CD4+ count, BMI, and total/HDL cholesterol at baseline, smoking, diabetes, hep B/C co-infection, use of lipid and BP lowering medication PLoS Medicine 2008; 5(10) e203
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Nested Case Control Design Time Axis 0 Two matched controls for every case were chosen. Follow-up for all members of the cohort (horizontal white lines) begins at randomization (zero-time axis).
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Baseline Biomarkers and All Cause Mortality: SMART Study Baseline Biomarkers and All Cause Mortality: SMART Study
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LECTURE 02 2011 - General Methods of Investigation 1 Chance...

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