Estimate Sobel's (1982) indirect test for mediation. The function provides
an estimate of the magnitude of the indirect effect, Sobel's first-order estimate of the standard error
associated with the indirect effect, and the corresponding z-value. The estimates are based
upon three models as detailed on page 84 of MacKinnon, Lockwood, Hoffman, West and Sheets (2002).
Usage
sobel(pred,med,out)
Arguments
pred
The predictor or independent variable (X).
med
The mediating variable (M).
out
The outcome or dependent variable (Y).
Value
Mod1: Y~X
A summary of coefficients from Model 1 of MacKinnon et al., (2002).
Mod2: Y~X+M
A summary of coefficients from Model 2 of MacKinnon et al., (2002).
Mod3: M~X
A summary of coefficients from Model 3 of MacKinnon et al., (2002).
Indirect.Effect
The estimate of the indirect mediating effect.
SE
Sobel's (1982) Standard Error estimate.
z.value
The estimated z-value.
N
The number of observations used in model estimation.
MacKinnon, D. P., Lockwood, C. M., Hoffman, J. M., West, S. G., Sheets, V. (2002). A
comparison of methods to test mediation and other intervening variable effects. Psychological
Methods, 7, 83-104.
Sobel, M. E., (1982). Asymptotic confidence intervals for indirect effects in structural equation
models. In S. Leinhardt (Ed.), Sociological Methodology 1982 (pp. 290-312). Washington, DC: American
Sociological Association.
Examples
data(bh1996)
#A small but significant indirect effect indicates leadership mediates
#the relationship between work hours and well-being.
sobel(pred=bh1996$HRS,med=bh1996$LEAD,out=bh1996$WBEING)