On tests and indices for evaluating structural models

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Abstract

Eight recommendations are given for the improved reporting of research based on structural equation modeling. These recommendations differ substantially from those offered by Prof. Barrett in this issue, especially with regard to the virtues and limitations of current statistical methods.

Introduction

Professor Barrett makes many wise and perceptive observations in his discussion of model fit, and I agree with much he says e.g., that investigators inappropriately ignore the test of model fit, that there are virtues to cross-validation, etc. Yet I also disagree with certain points, e.g., his recommendation to ban all fit indices. I will give my own recommendations on how a structural equation model (SEM) should be submitted to, and reported in, a journal, and compare these to Professor Barrett’s. See also McDonald and Ho (2002).

Section snippets

My Recommendations vs. Barrett’s

  • 1.

    When submitting a manuscript (ms) with an SEM, an author should submit a separate statement that verifies, for each major model, that (a) every parameter in the model is purely a priori, and if not, (b) details on all model modifications that were made. This material should be sent to reviewers along with the ms.

  • 2.

    Every ms should provide summary statistics, where these exist, for evaluating assumptions to be made in the statistical analysis. Example: if using a normal theory statistic for

On the sources of caution Re. test statistics

Barrett notes that the chosen probability level (e.g., reject the model if p < .05) on a χ2 test is arbitrary (true: why not .10, or .024), but “once that alpha level is set subjectively, … it becomes ‘exact’.” I disagree. As dozens of simulations across decades have shown, test statistics are not necessarily trustworthy (e.g., Curran et al., 1996, Hu et al., 1992). Even early proponents Jöreskog and Sörbom (1982, p.408) had reservations about their overall goodness of fit test: “… we emphasize

Approximate fit tests

If exact fit tests are not so exact, there may be a role for approximate fit. In discussing this, Barrett speaks negatively about recent work that tried to provide simulation-based guidance about the behavior of fit indices under null and non-null conditions. It seems to me helpful to know which indices are relatively insensitive to sample size, are sensitive to model misspecification, etc., even if the best recent research is not definitive. Perhaps SRMR needs little further research, since it

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Supported in part by National Institute on Drug Abuse Grants DA00017 and DA01070.

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