Description
This academic lecture by Dr. Wilbroad Mutale, presented for a 6th-year research methods course, provides an overview of key epidemiological study designs. It distinguishes between observational and experimental studies, detailing specific designs within each category. The material covers case reports/series, case-control studies (retrospective), cohort studies (prospective), and population studies, explaining their logic, advantages, disadvantages, and measures of effect like odds ratios. It then explains experimental studies, focusing on clinical trials, the importance of control groups, randomization, and blinding (single, double, triple) to minimize bias and establish causality. This resource is essential for tertiary-level students in medical, public health, and health sciences programs at the degree or postgraduate level, offering a foundational understanding of research methodology for designing and critically appraising studies. Download these notes to strengthen your knowledge of comparative study designs and their application in health research.
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6th year Research methods Study designs WILBROAD MUTALE(DR) CIDRZ lecture 31/10/07 Study designs CIDRZ lecture 31/10/07 Cohort studies Two main categories Observation: Identify subjects, then Observe and record characteristics CIDRZ lecture 31/10/07 Cohort studies Observation vs Experiment Observations are readily obtained, but subject to bias, that is systematic errors Some observational designs are less subject to bias than others CIDRZ lecture 31/10/07 Cohort studies Observation vs Experiment Experiments are hard to do well • Experiments can answer narrow questions definitively Generalizability of results from experiments may be at issue, eg new drug testing that excludes women subjects CIDRZ lecture 31/10/07 Cohort studies Experiment: Identify subjects, Place in common context, Intervene, then Observe effects of intervention CIDRZ lecture 31/10/07 Cohort studies Observational studies Case Series Case-control studies Cohort Studies Population studies (e.g Ecological) CIDRZ lecture 31/10/07 Cohort studies Case report/ series • Example: “Normal plasma cholesterol in an 88-year-old man who eats 25 eggs a day”(Case report) Then followed by similar cases else where(series) CIDRZ lecture 31/10/07 Cohort studies Advantages of case reports/ series Excellent at identifying unusual situation Good for generating hypotheses amenable to rigorous test Disadvantages CIDRZ lecture 31/10/07 Cohort studies Disadvantages Generally short-term Investigators self-select (bias!) Generally no controls CIDRZ lecture 31/10/07 Cohort studies Case-control studies Controlled studies Retrospective How are Case-Control Studies Done? CIDRZ lecture 31/10/07 Cohort studies Identify cases (with condition of interest, here, eg.coccidioidomycosis) Match to disease-free controls who are similar with respect to known risk factors for condition Compare degree of exposure to possible risk factor (e.g exposure to dust cloud). 6th year 2014 The logic ofCase-Control Studies Cases differ from controls only in having the Disease. If exposure does not predispose to having the disease, then exposure should be equally distributed between the cases and controls. The extent of greater previous exposure among the cases reflects the increased risk that exposure confers Measures of effect: Relative risk (ratio of probabilities of contracting disease given exposure), or Odds ratio (ratio of the odds of contracting disease given exposure) OR of 1 indicate no effect of exposure (equal odds) • “Physically being in a dust cloud (OR 3.0; CI, 1.6-5.4; P<.001) significantly increased the risk for being diagnosed with coccidioidomycosis” Cohort studies Prospective Controlled Can determine causes and incidence of diseases as well as identify risk factors Generally expensive and difficult to carry out Procedure for cohort study Procedure for cohort study Identify groups of exposed subjects and control Match for other risk factors Follow over time Record the fraction in each group who develop the condition of interest Compare these fractions using RR Logic of the cohort study Differences in the rate at which exposed and control subjects contract a disease is due to the differences in exposure, since other known risk factors are equally present in the two groups Experimental studies Clinical trials: A clinical trial is a comparative, prospective experiment conducted in human or animal subjects. Controlled vs Uncontrolled studies Controlled: Comparison made relative to a simultaneous reference group. Uncontrolled: Comparison implicit eg: -Previous experience -Historical evidence -Anecdote -Other Controlled trials… Inference: Controlled trial …make it possible to ascribe differences in outcome to differences in treatment CIDRZ lecture 31/10/07 Cohort studies Randomization & Concurrent Controls Randomized vs nonrandomized assignment to Rx “The randomized clinical trial is the epitome of all research designs because it provides the strongest evidence for concluding causation.” Conclusions from non randomized studies subject to many sources of bias Randomization & Concurrent Controls Patients can serve as own controls This is usually beneficial The comparison removes patient differences. 6/25/23 6th year Lecture series Example Subjects received placebo eye drops in one eye, Vasocon-A drops in the other eye Randomization determined which eye gets placebo for each pt Cat-dander extract applied to both eyes Response between eyes compared. Subjects received placebo Blinding Good practice: factors that can affect the evaluation of outcome should not be permitted to influence the evaluation process: Double-blind design Neither patient nor outcome evaluator knows Rx to which patient was assigned Single-blind Patient or evaluator is blinded as to Rx, but not both Triple-blind Patient, Physician, and Data analyst are blinded as to Rx Thank you for your attention CIDRZ lecture 31/10/07 Cohort studies
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