Reader response: Twenty-seven-year time trends in dementia incidence in Europe and the United States: The Alzheimer Cohorts Consortium
JonathanSpiegel, Medical Student, Brown University's Warren Alpert School of Medicine
Monyde Leon, Director Brain Health Imaging Institute, Brain Health Imaging Institute at Weill Cornell Medicine Department of Radiology
Submitted August 26, 2020
Using several large longitudinal cohorts, Wolters et al.1 recently reported that the age-adjusted incidence of dementia has declined over recent decades by 13% per decade.
We wanted to inquire whether the authors considered the potential impact repeat testing and associated learning effects may have had on their data. Repeat testing within cohorts can diminish a test’s sensitivity for detecting dementia.2 Consequently, the sensitivity for detecting dementia may decrease over time within serially tested cohorts, such as the ones Wolter et al. examined.
In a related study, without considering practice effects, Hale et al. found dementia prevalence to decrease by 13% per decade.2 However, when they accounted for potential practice effects, they found dementia prevalence to increase—not decrease—by 29% per decade.
Hale et al.’s study demonstrates that practice effects can bias results to show an artificial decrease in the prevalence of dementia. Studies are therefore needed to determine the degree to which age-adjusted dementia incidence rates measured in longitudinal cohorts are impacted by practice effects.
Disclosure
The authors report no relevant disclosures. Contact journal@neurology.org for full disclosures.
References
Wolters FJ, Chibnik LB, Waziry R, et al. 27-year time trends in dementia incidence in Europe and the US: the Alzheimer Cohorts Consortium. Neurology. 2020;95:e519–e531.
Hale JM, Schneider DC, Gampe J, Mehta NK, Myrskylä M. Trends in the Risk of Cognitive Impairment in the United States, 1996-2014. Epidemiology 2020;31:745–754.
Using several large longitudinal cohorts, Wolters et al.1 recently reported that the age-adjusted incidence of dementia has declined over recent decades by 13% per decade.
We wanted to inquire whether the authors considered the potential impact repeat testing and associated learning effects may have had on their data. Repeat testing within cohorts can diminish a test’s sensitivity for detecting dementia.2 Consequently, the sensitivity for detecting dementia may decrease over time within serially tested cohorts, such as the ones Wolter et al. examined.
In a related study, without considering practice effects, Hale et al. found dementia prevalence to decrease by 13% per decade.2 However, when they accounted for potential practice effects, they found dementia prevalence to increase—not decrease—by 29% per decade.
Hale et al.’s study demonstrates that practice effects can bias results to show an artificial decrease in the prevalence of dementia. Studies are therefore needed to determine the degree to which age-adjusted dementia incidence rates measured in longitudinal cohorts are impacted by practice effects.
Disclosure
The authors report no relevant disclosures. Contact journal@neurology.org for full disclosures.
References