(c) B. Gerstman 2007Chapter 101 Epidemiology Kept Simple Chapter 10 Experimental Studies

(c) B. Gerstman 2007Chapter 102 Introduction Recall the definition of an experiment Trials - from the French trier (to try) Clinical trial – apply therapeutic interventions to sick individuals (e.g., chemotherapy trial) Field trial – apply preventive interventions to healthy individuals (e.g., vaccine trial) Community trial – apply interventions to aggregate units (e.g., fluoridation of public water)

(c) B. Gerstman 2007Chapter 103 Natural “Experiment” Natural conditions mimic an intervention French surgeon Paré (1510–1590) ran out of boiling oil used to treat wounds –Was forced to use an innocuous lotion as treatment –Noticed vast improvement Not true experiment (intervention not assigned as part of protocol)

(c) B. Gerstman 2007Chapter 104 Selected Concepts All except #2 apply to observational designs as well 1.Control group 2.Randomization 3.Admissibility criteria 4.Outcome ascertainment 5.Ethics

(c) B. Gerstman 2007Chapter 105 Element 1. Control Group The effects of an exposure can only be judged in comparison to what would happen in its absence The control group provides this comparison ExposedNot exposed

(c) B. Gerstman 2007Chapter 106 Illustration: “MRFIT” Multiple Risk Factor Intervention Trial Exposure: Health education vs. no special intervention Outcome: CVD Treatment group experienced dramatic declines in CVD But so did the control group Rates were declining in all groups in the 1970s Effect of the intervention was negligable

(c) B. Gerstman 2007Chapter 107 Effects from inert interventions Placebo effect – improvement associated with inert interventions Placebo effects are a scientific mystery

(c) B. Gerstman 2007Chapter 108 Effects from inert interventions Hawthorne effect – subjects improve an aspect of their behavior being experimentally measured simply in response to the fact that they are being studied, not in response to any particular experimental manipulation. From the field of industrial psychology

(c) B. Gerstman 2007Chapter 109 Element 2. Randomization Randomization works by balancing extraneous determinants in the groups being compared, thus mitigating confounding

(c) B. Gerstman 2007Chapter 1010 How randomization works Suppose you want to determine whether a particular diet (the exposure) is associated with improved weight gain in lab animals (outcome) Randomization encourages equal numbers of fast-growing rats in each group

(c) B. Gerstman 2007Chapter 1011 Polio Field Trial (1954) Polio rates (per 100,000) Placebo 69 Refusers 46 Vaccinated 28 Note: Had refusers been used as the control group, the effects of the intervention would have been underrated (Am J Pub Health, 1957, 47: 283-7)Am J Pub Health, 1957, 47: Dr. Jonas Salk, 1953

(c) B. Gerstman 2007Chapter Admissibility Criteria Restrict participants to those with uniform characteristics This too mitigates confounding Example: Excluding smokers from a study base would prevent confounding from smoking

(c) B. Gerstman 2007Chapter Outcome Ascertainment Outcome ascertainments must be valid Without valid outcome ascertainment, we have GIGO (garbage in, garbage out) We will study the importance of valid information in Ch 12

(c) B. Gerstman 2007Chapter Ethics The Belmont Report –Respect for individuals –Beneficence –Justice Other considerations –IRB oversight –Informed consent

(c) B. Gerstman 2007Chapter 1015 Equipoise Equipoise ≡ balanced doubt Cannot knowingly expose a participant to harm Cannot withhold known benefit What’s left? ANS: balanced doubt Is equipoise the over-riding concept behind the ethical principles of respect for individuals, beneficence, & justice?