1 Chapter 6 SAMPLE SIZE ISSUES Ref: Lachin, Controlled Clinical Trials 2:93-113, 1981

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3 Example: How many subjects? Compare new treatment (T) with a control (C) Previous data suggests Control Failure Rate (P c ) ~ 40% Investigator believes treatment can reduce P c by 25% i.e. P T =.30, P C =.40 N = number of subjects/group?