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The Reliability Factor: Modeling Individual Reliability with Multiple Items from a Single Assessment

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Abstract

Reliability is a crucial concept in psychometrics. Although it is typically estimated as a single fixed quantity, previous work suggests that reliability can vary across persons, groups, and covariates. We propose a novel method for estimating and modeling case-specific reliability without repeated measurements or parallel tests. The proposed method employs a “Reliability Factor” that models the error variance of each case across multiple indicators, thereby producing case-specific reliability estimates. Additionally, we use Gaussian process modeling to estimate a nonlinear, non-monotonic function between the latent factor itself and the reliability of the measure, providing an analogue to test information functions in item response theory. The reliability factor model is a new tool for examining latent regions with poor conditional reliability, and correlates thereof, in a classical test theory framework.

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Notes

  1. Note that the reliability factor models error variance in responses, and not intraindividual variability of responses, nor variance in latent factors.

  2. A traditional Gaussian model assumes that, e.g., \(y \sim {\mathcal {N}}(\mu = f(X), \sigma ^2)\). A location-scale Gaussian model includes a second submodel on the scale parameter, \(\sigma ^2\), to model variance: \(y \sim {\mathcal {N}}(\mu = f(X), \sigma ^2 = g(X))\). Because \(\sigma ^2\) must be positive, a log-link function is used in the submodel, \(\sigma ^2 = \exp (g(X))\). The reliability factor approach uses this exact strategy in its formulation.

  3. The latent factors (\({\varvec{\eta _i}}\)) can be endogenously modeled as per usual, but this is not discussed here.

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Data Availability Statement

The datasets generated during the current study are available from the corresponding author on request. The Holzinger–Swineford (1939) dataset is freely available in the lavaan (https://cran.r-project.org/web/packages/lavaan/index.html) and MBESS (https://cran.r-project.org/web/packages/MBESS/index.html) R packages.

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Research reported in this publication was supported by the National Institute On Aging of the National Institutes of Health under Award Number R01AG050720 to PR. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

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Martin, S.R., Rast, P. The Reliability Factor: Modeling Individual Reliability with Multiple Items from a Single Assessment. Psychometrika 87, 1318–1342 (2022). https://doi.org/10.1007/s11336-022-09847-9

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  • DOI: https://doi.org/10.1007/s11336-022-09847-9

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