BACKGROUND This article explores the suitability of a proposed "Dual" model, in which both people and items are sources of measurement error, by assessing how the test scores are expected to behave in terms of marginal reliability and external validity when the model holds. METHOD Analytical derivations are produced for predicting: (a) the impact of person and item errors in the amount of marginal reliability and external validity, as well as the occurrence of "ceiling" effects; (b) the changes in test reliability across groups with different average amounts of person error, and (c) the phenomenon of differential predictability. Two empirical studies are also used both as an illustration and as a check of the predicted results. RESULTS Results show that the model-based predictions agree with existing evidence as well as with basic principles in classical test theory. However, the additional inclusion of individuals as a source of error leads to new explanations and predictions. CONCLUSIONS The proposal and results provide new sources of information in personality assessment as well as of evidence of model suitability. They also help to explain some disappointing recurrent results.

中文翻译：

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人格测试分数的可靠性和外部有效性：人和项目错误的作用。

背景本文通过评估测试分数在模型成立时的边际可靠性和外部有效性方面的预期表现，探讨了所提出的“双重”模型的适用性，其中人和项目都是测量误差的来源。方法 分析推导用于预测： (a) 人和项目错误对边际信度和外部效度的影响，以及“上限”效应的发生；(b) 具有不同平均人员错误量的组之间测试可靠性的变化，以及 (c) 差异可预测性的现象。两项实证研究也用作说明和对预测结果的检查。结果 结果表明，基于模型的预测与现有证据以及经典测试理论的基本原则一致。然而，将个人作为错误来源的额外包含导致了新的解释和预测。结论 该提议和结果为人格评估以及模型适用性的证据提供了新的信息来源。它们还有助于解释一些令人失望的重复结果。