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How many subjects?

Learn how to determine the ideal sample size for regression analysis using formulas from Sam Green and Cohen's sample size charts. Get expert advice on subjects per IV and effect size calculations.

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How many subjects?

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  1. How many subjects?

  2. Recommendations • At least 100 subjects? • 30 subjects per one IV? • Sample size charts by Cohen (1988) in “Statistical power analysis for the behavioral sciences” • Sam Green’s formulas Green, S. (1991). How many subjects does it take to do a regression analysis? Multivariate Behavioral Research, 26, 499-510. • G*Power (http://www.psycho.uni-duesseldorf.de/abteilungen/aap/gpower3/)

  3. Sam Green’s Formulas • Determine the effect size . • Convert to . • Use the formula. Where e.g.,

  4. Another formula • When a specific regression coefficient to be tested:

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