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 & Hanges, 2004).
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 |
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. |
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) #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))