sobel.lme {multilevel}R Documentation

Estimate Sobel's (1982) Test for Mediation in Two-Level lme Model

Description

Estimate Sobel's (1982) indirect test for mediation in a two-level linear mixed effects (lme) model. 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). By estimating the three models in a two-level lme framework, one can account for the effects of hierarchical nesting in the data, and thereby obtain more accurate estimates of standard errors (see Bliese & Hanges, 2004).

Usage

sobel.lme(pred, med, out, grpid)

Arguments

pred The predictor or independent variable.
med The mediating variable.
out The outcome or dependent variable.
grpid A variable identifying the groups in which pred, med and out are nested.

Value

Model.1 Summary of coefficients from Model 1 of MacKinnon et al.
Model.2 Summary of coefficients from Model 2 of MacKinnon et al.
Model.3 Summary of coefficients from Model 3 of MacKinnon et al.
Indirect.Effect Estimate of 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.
n.grps The number of groups used in model estimation.

Author(s)

Paul Bliese paul.bliese@us.army.mil

References

Bliese, P. D. & Hanges, P. J. (2004). Being both too liberal and too conservative: The perils of treating grouped data as though they were independent. Organizational Research Methods, 7, 400-417.

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.

See Also

sobel

Examples

data(bh1996)
library(nlme)

#A small but significant indirect effect indicates leadership mediates
#the relationship between work hours and well-being.

with(bh1996, sobel.lme(pred=HRS,med=LEAD,out=WBEING,grpid=GRP))

[Package multilevel version 2.3 Index]