SAMPLE SIZE DETERMINATION

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SAMPLE SIZE DETERMINATION . Dr. M. H. Rahbar Professor of Biostatistics Department of Epidemiology Director, Data Coordinating Center College of Human Medicine Michigan State University. Important Statistical Terms.

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SAMPLE SIZE DETERMINATION

Dr. M. H. Rahbar

Professor of Biostatistics

Department of Epidemiology

Director, Data Coordinating Center

College of Human Medicine

Michigan State University

Important Statistical Terms
• Population:A set which includes all measurements of interest to the researcher
• Sample: Any subset of the population
• Parameter of interest: The characteristic of interest to the researcher in the population is called a parameter
INFERENTIAL STATISTICS
• Estimation: This includes point and interval estimation of certain characteristics in the population(s). (e.g., Means, proportions)
• Testing Hypothesis about population parameter(s) based on the information contained in the sample(s)

Confidence Intervals for population Mean, µ

95% C.I. For , when n30, is

Confidence Intervals for Prevalence of a disease in a population (or Proportion P)95% C.I. For Prevalence P is

QUESTION: Do persons with the disease have higher blood levels of “factor X” than those without disease?

Risk Factors for Myocardial Infarction (MI)

Null Hypothesis: There is no association between hypertension and Myocardial Infarction, or P1=P2, where P1 and P2 are the prevalence of hypertension among cases and controls respectively.

Alternative Hypothesis: There is an association between hypertension and Myocardial Infarction, P1P2.

Sample size determination for a 1:1 case control Ratio
• A study with 250 cases, 250 controls will safely detect risk factors with an odds ratio of three or more, unless they are extremely common or extremely uncommon
• We have a good chance of detecting factors with an odds ratio of two to three, providing their prevalence in the source population is between about 20% and 70%.
Sample size determination for a 1: k case control Ratio
• When it is difficult to recruit sufficient cases during the intended study period, the power may be increased by selecting more than one control per case.
• For details you may want to see standard Epidemiology textbooks.