ss.power.rc: sample size for a targeted regression coefficient In MBESS: The MBESS R Package

Description

Determine the necessary sample size for a targeted regression coefficient or determine the degree of power given a specified sample size

Usage

 1 2 3 4 5 6 ss.power.rc(Rho2.Y_X = NULL, Rho2.Y_X.without.k = NULL, K = NULL, desired.power = 0.85, alpha.level = 0.05, Directional = FALSE, beta.k = NULL, sigma.X = NULL, sigma.Y = NULL, Rho2.k_X.without.k = NULL, RHO.XX = NULL, Rho.YX = NULL, which.predictor = NULL, Cohen.f2 = NULL, Specified.N = NULL, Print.Progress = FALSE)

Arguments

 Rho2.Y_X population squared multiple correlation coefficient predicting the dependent variable (i.e., Y) from the p predictor variables (i.e., the X variables) Rho2.Y_X.without.k population squared multiple correlation coefficient predicting the dependent variable (i.e., Y) from the K-1 predictor variables, where the one not used is the predictor of interest K number of predictor variables desired.power desired degree of statistical power for the test of targeted regression coefficient alpha.level Type I error rate Directional whether or not a direction or a nondirectional test is to be used (usually directional=FALSE) beta.k population value of the regression coefficient for the predictor of interest sigma.X population standard deviation for the predictor variable of interest sigma.Y population standard deviation for the outcome variable Rho2.k_X.without.k population squared multiple correlation coefficient predicting the predictor variable of interest from the remaining K-1 predictor variables RHO.XX population correlation matrix for the p predictor variables Rho.YX population vector of correlation coefficient between the p predictor variables and the criterion variable which.predictor identifies the predictor of interest when RHO.XX and Rho.YX are specified Cohen.f2 Cohen's (1988) definition for an effect size for a targeted regression coefficient: (Rho2.Y_X-Rho2.Y_X.without.j)/(1-Rho2.Y_X) Specified.N sample size for which power should be evaluated Print.Progress if the progress of the iterative procedure is printed to the screen as the iterations are occurring

Details

Determines the necessary sample size given a desired level of statistical power. Alternatively, determines the statistical power for a given a specified sample size. There are a number of ways that the specification regarding the size of the regression coefficient can be entered. The most basic, and often the simplest, is to specify Rho2.Y_X and Rho2.Y_X.without.k. See the examples section for several options.

Value

 Sample.Size either the necessary sample size or the specified sample size, depending if one is interested in determining the necessary sample size given a desired degree of statistical power or if one is interested in the determining the value of statistical power given a specified sample size, respectively Actual.Power Actual power of the situation described Noncentral.t.Parm value of the noncentral distribution for the appropriate t-distribution Effect.Size.NC.t effect size for the noncentral t-distribution; this is the square root of Cohen.f2, because Cohen.f2 is the effect size using an F-distribution

Author(s)

Ken Kelley (University of Notre Dame; KKelley@ND.Edu)

References

Maxwell, S. E. (2000). Sample size for multiple regression. Psychological Methods, 4, 434–458.

Cohen, J. (1988). Statistical power analysis for the behavioral sciences (2nd ed.). Hillsdale, NJ: Erlbaum.