IBM® SPSS® Amos™ 28

Seven measures of fit, NFI, RFI, IFI, TLI, CFI, PNFI, and PCFI, require a "null" or "baseline" bad model against which other models can be compared. The specification search procedure offers a choice of four null, or baseline, models:

▪Null 1: The observed variables are required to be uncorrelated. Their means and variances are unconstrained. This is the baseline "Independence" model in an ordinary Amos analysis when you do not perform a specification search.

▪Null 2: The correlations among the observed variables are required to be equal. The means and variances of the observed variables are unconstrained.

▪Null 3: The observed variables are required to be uncorrelated and to have zero means. Their variances are unconstrained. This is the baseline "Independence" model used by Amos 4.0.1 and earlier for models where means and intercepts are explicit model parameters.

▪Null 4: The correlations among the observed variables are required to be equal. The variances of the observed variables are unconstrained. Their means are required to be zero.

Each null model gives rise to a different value for NFI, RFI, IFI, TLI, CFI, PNFI, and PCFI.

Models Null 3 and Null 4 are fitted during a specification search only when means and intercepts are explicitly estimated in the models you specify. The Null 3 and Null 4 models may be appropriate when evaluating models in which means and intercepts are constrained. There is little reason to fit the Null 3 and Null 4 models in the common situation where means and intercepts are not constrained, but are estimated for the sole purpose of allowing maximum likelihood estimation with missing data.

To specify which baseline models you want to be fitted during specification searches, do the following:

oClick the Options button on the Specification Search toolbar.

oIn the Options dialog box, click the Next search tab.

The four null models, along with the saturated model, are listed in the Benchmark models group.