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Mov Disord. 2018 May;33(5):839-843. doi: 10.1002/mds.27335. Epub 2018 Feb 14.

Selection of Normative Group Affects Rates of Mild Cognitive Impairment in Parkinson's Disease.

Author information

1
HealthPartners Neuroscience Center, Saint Paul, MN.
2
HealthPartners Institute, Bloomington, MN.
3
University of Virginia, Department of Neurology, Charlottesville, VA.
4
University of Kansas School of Medicine-Wichita, Department of Psychiatry and Behavioral Sciences, Wichita, KS.
5
Departments of Psychiatry and Neurology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA.
6
Parkinson's Disease and Mental Illness Research, Education and Clinical Centres, Philadelphia Veterans Affairs Medical Centre, Philadelphia, PA.

Abstract

OBJECTIVE:

The objective of this study was to examine the impact of different methods of standardizing cognitive data in the Parkinson's Progression Marker Initiative.

METHODS:

Cognitive data from 423 participants with Parkinson's disease were included (age = 61.7 [9.7], education = 15.6 [3.0]). Internal norms were calculated using the group mean and standard deviation of the healthy control group. Published norms were compared to the overall group mean of and to age-stratified norms from healthy controls for each neuropsychological test over 4 visits. Rates of mild cognitive impairment were calculated using established criteria.

RESULTS:

The use of internal norms resulted in lower standardized scores than published norms on all tests with the exception of memory and processing speed (P ≤ .001). Individuals were 1.5 to 2.1 times more likely to be diagnosed with mild cognitive impairment using internal norms than published norms.

CONCLUSIONS:

Standardization approaches with cognitive data are not interchangeable. Selection of a normative comparison group impacts research and clinical interpretations of cognitive data. © 2018 International Parkinson and Movement Disorder Society.

KEYWORDS:

Parkinson's disease; cognitive data; neuropsychology

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