LECTURE 12 2011

LECTURE 12 2011 - Common Designs for Controlled Clinical...

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Common Designs for Controlled Clinical Trials A. Parallel Group Trials 1. Simplest example - 2 groups, no stratification 2. Stratified design 3. Matched pairs 4. Factorial design B. Crossover Trials
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Epidemiology of Randomized Trials Among 519 trials published in December 2000 74% were parallel group with a median enrollment of 80 participants total 22% were crossover with a median of 15 participants Lancet 2005; 365:1159-1162.
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Parallel Group Studies Informed Consent Yes, randomize No Eligible Patients A B Variability of response = σ 2 σ 2 = between subject σ 2 within subject σ 2 = σ 2 + e s +
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Parallel Group Studies Stratified Randomization Informed Consent Yes No Eligible Patients Stratum 1 Stratum i Stratum 2 . . . A B A B A B Variability of response = σ 2 = σ 2 + ie is σ 2 i w i σ 2 i
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Parallel Group “Switchover” Trial: A Simple Example of A Dynamic Treatment Regimen (Treatment Individualized to Patient) Randomize A B Eligible Patients Informed Consent Use B if A fails Use A if B fails
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Didanosine (ddI) versus Zalcitabine (ddC) for Patients with Advanced HIV RANDOMIZATION ddI ddC Patient Who Failed on AZT OR Intolerant to AZT If fail/ intolerant If fail/ intolerant ddC ddI N Engl J Med 1994; 330:657-
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Another Example: Invasive versus Conservative Management Strategy for Acute non-Q-wave Myocardial Infarction (VANQUISH Trial) Invasive: coronary angiography as the initial diagnostic test Conservative: radionuclide ventriculography followed by a symptom-limited treadmill test with thallium scintigraphy Coronary angiography performed if: Recurrent post-infarction angina with ischemic ECG changes ST segment depression during peak exercise Redistribution defects on scintigraphy N Engl J Med 1998; 338:1785-1792
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Parallel Group Studies: 2 x 2 Factorial Design – both A and B Controlled Experimentally Informed Consent Yes, randomize No Eligible Patients A, no B No A, no B A, B Variability of response = σ 2 = σ 2 + ie is σ 2 i w i σ 2 i No A, B Two factors each at 2 levels = 2x2.
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Factorial Design In the literature the term “factorial design” is also used to refer to observational studies (e.g., of two observed factors) or of an experimental study of a single factor with stratification by a baseline factor. While the general analysis of such studies is similar, these designs are very different from an experimental study of two factors (that is the focus here).
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Parallel Group Study Factorial Design Another Representation A B No B No A B No B Note: This is different than recording factor A (Y/N) and/or possibly using it as a stratifying variable. The analysis of the effect of B versus no B is similar but inferences are different.
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Example: 2x2 factorial study of pain from peripheral neuropathy for individuals with HIV
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LECTURE 12 2011 - Common Designs for Controlled Clinical...

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