sobel.lme {multilevel} | R Documentation |
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 and Hanges, 2002).
sobel.lme(pred, med, out, grpid)
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. |
Model.1 |
A summary of coefficients from Model 1 of MacKinnon et al., (2002). |
Model.2 |
A summary of coefficients from Model 2 of MacKinnon et al., (2002). |
Model.3 |
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. |
n.grps |
The number of groups used in model estimation. |
Paul Bliese paul.bliese@us.army.mil
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.
data(bh1996) library(nlme) sobel.lme(pred=bh1996$HRS,med=bh1996$LEAD,out=bh1996$WBEING,grpid=bh1996$GRP) #A small but significant indirect effect indicates leadership mediates #the relationship between work hours and well-being.