Restricted accessResearch articleFirst published online 2018-6-8
Time Trends in the Prevalence of Neurocognitive Disorders and Cognitive Impairment in the United States: The Effects of Disease Severity and Improved Ascertainment
Trends in the prevalence of cognitive impairment (CI) based on cognitive assessment instruments are often inconsistent with those of neurocognitive disorders (ND) based on Medicare claims records.
Objective:
We hypothesized that improved ascertainment and resulting decrease in disease severity at the time of diagnosis are responsible for this phenomenon.
Methods:
Using Medicare data linked to the Health and Retirement Study (1992–2012), we performed a joint analysis of trends in CI and ND to test our hypothesis.
Results:
We identified two major contributors to the divergent directions in CI and ND trends: reductions in disease severity explained more than 60% of the differences between CI and ND prevalence over the study period; the remaining 40% was explained by a decrease in the fraction of undiagnosed individuals.
Discussion:
Improvements in the diagnoses of ND diseases were a major contributor to reported trends in ND and CI. Recent forecasts of CI and ND trends in the U.S. may be overly pessimistic.
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