Spectrum Effect and Spectrum Bias in the Screening Test Performance for Amnestic Mild Cognitive Impairment: What are the Clinical Implications?

Abstract

A single cutoff is widely used to screen amnestic mild cognitive impairment (aMCI). However, results of screening test performance are never adjusted for spectrum effect and spectrum bias. To assess the potential impact of spectrum effect and spectrum bias on screening test performance and clinical decision. The ability of the combination of Memory Impairment Screen (MIS), the Isaacs Set Test (IST), and the Mini-Mental State Examination (MMSE) to distinguish aMCI (n = 3,330) from patients with subjective cognitive complaints (SCC) (n = 1,522) was investigated across a wide range of age and educational backgrounds. The spectrum effect was defined as the variation of the sensitivity and/or the specificity across different subgroups. A spectrum bias was highlighted if the likelihood ratio (LR) observed in a subgroup of subjects statistically differed from the LR observed in the overall sample. For the MIS-IST pairing, the overall sensitivity and specificity were equal to 72.5% and 75.2% , the positive LR (LR+) and the negative LR (LR-) were equal to 2.91 and 0.37, respectively. Across the different age-education subgroups, the sensitivities ranged from 43.7% to 92.5% and specificities from 39.3% to 95.2%. LR+ and LR- ranged from 1.51 to 9.10 and 0.13 to 0.59, respectively. A statistically significant spectrum bias was found in some subgroups and may result in differences between the post-test probabilities. Similar results were also found for the MMSE. These findings could potentially affect the clinician's decision with a possible greater impact in elderly patients with a lower educational level.