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Bayesian Estimation of Values Other Than Model Parameters
Inferences about Indirect Effects
There are two methods for finding a confidence interval for an indirect effect or for
testing an indirect effect for significance. Sobel (1982, 1986) gives a method that
assumes that the indirect effect is normally distributed. A growing body of statistical
simulation literature calls into question this assumption, however, and advocates the
use of the bootstrap to construct better, typically asymmetric, confidence intervals
(MacKinnon, Lockwood, and Williams, 2004; Shrout and Bolger, 2002). These studies
have found that the bias-corrected bootstrap confidence intervals available in Amos
produce reliable inferences for indirect effects.
As an alternative to the Sobel method and the bootstrap for finding confidence
intervals, Amos can provide (typically asymmetric) credible intervals for standardized
or unstandardized indirect effects. The next figure shows the lower boundary of a 95%
credible interval for each standardized indirect effect in the model. Notice that
95%
Lower bound
is selected in the panel at the left of the Additional Estimands window.
(You can specify a value other than 95% in the Bayesian Sem Options dialog box.)