powerMediation.VSMc {powerMediation}R Documentation

Power for testing mediation effect based on Vittinghoff and McCulloch's (2009) method

Description

Calculate Power for testing mediation effect based on Vittinghoff and McCulloch's (2009) method.

Usage

powerMediation.VSMc(n, b2, sigma.m, sigma.e, corr.xm, alpha = 0.05, 
  verbose = TRUE)

Arguments

n sample size.
b2 regression coefficient for the mediator m in the linear regression y_i=b0+b1 x_i + b2 m_i + \epsilon_i, \epsilon_i\sim N(0, \sigma_e^2).
sigma.m standard deviation of the mediator.
sigma.e standard deviation of the random error term in the linear regression y_i=b0+b1 x_i + b2 m_i + \epsilon_i, \epsilon_i\sim N(0, \sigma_e^2).
corr.xm correlation between the predictor x and the mediator m.
alpha type I error rate.
verbose logical. TRUE means printing power; FALSE means not printing power.

Details

The power is for testing the null hypothesis b_2=0 versus the alternative hypothesis b_2\neq 0 for the linear regressions:

y_i=b_0+b_1 x_i + b_2 m_i + \epsilon_i, \epsilon_i\sim N(0, \sigma^2_{e})

Vittinghoff et al. (2009) showed that for the above linear regression, testing the mediation effect is equivalent to testing the null hypothesis H_0: b_2=0 versus the alternative hypothesis H_a: b_2\neq 0.

Value

power power for testing if b_2=0.
delta b_2\sigma_m\sqrt{1-\rho_{xm}}/\sigma_e, where \sigma_m is the standard deviation of the mediator m, \rho_{xm} is the correlation between the predictor x and the mediator m, and \sigma_e is the standard deviation of the random error term in the linear regression.

Note

The test is a two-sided test. Code for one-sided tests will be added later.

Author(s)

Weiliang Qiu stwxq@channing.harvard.edu

References

Vittinghoff, E. and Sen, S. and McCulloch, C.E.. Sample size calculations for evaluating mediation. Statistics In Medicine. 2009;28:541-557.

See Also

minEffect.VSMc, ssMediation.VSMc

Examples

  powerMediation.VSMc(n=100, b2=0.8, sigma.m=0.1, sigma.e=0.2, corr.xm=0.5, 
    alpha = 0.05, verbose = TRUE)

[Package powerMediation version 0.0.6 Index]