Abstract
Background: 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.
Objectives: To assess the potential impact of spectrum effect and spectrum
bias on screening test performance and clinical decision.
Methods: 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.
Results: 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.
Conclusion: These findings could potentially affect the clinician’s decision
with a possible greater impact in elderly patients with a lower educational level.
