INTRODUCTION: The Clinical Dementia Rating (CDR) Scale is a gold standard for staging impairment in Alzheimer's disease and other dementias (ADRD). The Quick Dementia Rating System (QDRS) offers similar results in 3 to 5 minutes without a trained clinician. This study aimed to (1) investigate concordance between comparably derived QDRS and CDR global scores, (2) examine item‐level QDRS/CDR agreement, and (3) compare sample characteristics and cognitive performance across QDRS/CDR global concordant/discordant groups. METHODS: The study included 351 QDRS/CDR pairs from 297 participants in the Wisconsin Registry for Alzheimer's Prevention (WRAP). Analyses included descriptive indices of QDRS/CDR agreement, lasso logistic regression, tetrachoric correlations, and linear mixed models. RESULTS: The QDRS global/CDR global concordance rate is 70.66%. Memory item discrepancies were primarily responsible for QDRS/CDR global rating discordance. Average cognitive scores were highest in concordant‐normal QDRS/CDR and lowest in concordant‐abnormal QDRS/CDR. DISCUSSION: The QDRS effectively screened for impairment in this sample. Future analyses will investigate QDRS relations to ADRD biomarkers. Highlights: The Quick Dementia Rating System (QDRS) effectively screened for impairment in Alzheimer's disease and other dementias (ADRD) in a non‐demented sample. Concordance rate between QDRS _CDR global and Clinical Dementia Rating (CDR) Scale global scores is 70.66%. Memory item discrepancies primarily cause QDRS/CDR global score discordance. Cognitive scores are associated with QDRS/CDR concordances/discordances. Future analyses will explore QDRS relations to ADRD biomarkers.

Previous studies have demonstrated evidence of latent skill continuity even in tests intentionally designed for measurement of binary skills. In addition, the assumption of binary skills when continuity is present has been shown to potentially create a lack of invariance in item and latent ability parameters that may undermine applications. In this article, we examine measurement of growth as one such application, and consider multidimensional item response theory (MIRT) as a competing alternative. Motivated by prior findings concerning the effects of skill continuity, we study the relative robustness of cognitive diagnostic models (CDMs) and (M)IRT models in the measurement of growth under both binary and continuous latent skill distributions. We find CDMs to be a less robust way of quantifying growth under misspecification, and subsequently provide a real-data example suggesting underestimation of growth as a likely consequence. It is suggested that researchers should regularly attend to the assumptions associated with the use of latent binary skills and consider (M)IRT as a potentially more robust alternative if unsure of their discrete nature.

Binary examinee mastery/nonmastery classifications in cognitive diagnosis models may often be an approximation to proficiencies that are better regarded as continuous. Such misspecification can lead to inconsistencies in the operational definition of “mastery” when binary skills models are assumed. In this paper we demonstrate the potential for an interpretational confounding of the latent skills when truly continuous skills are treated as binary. Using the DINA model as an example, we show how such forms of confounding can be observed through item and/or examinee parameter change when (1) different collections of items (such as representing different test forms) previously calibrated separately are subsequently calibrated together; and (2) when structural restrictions are placed on the relationships among skill attributes (such as the assumption of strictly nonnegative growth over time), among other possibilities. We examine these occurrences in both simulation and real data studies. It is suggested that researchers should regularly attend to the potential for interpretational confounding by studying differences in attribute mastery proportions and/or changes in item parameter (e.g., slip and guess) estimates attributable to skill continuity when the same samples of examinees are administered different test forms, or the same test forms are involved in different calibrations.