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

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


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Age Factors
  • Aged
  • Cognitive Dysfunction / diagnosis*
  • Cognitive Dysfunction / etiology*
  • Disease Progression
  • Female
  • Follow-Up Studies
  • Humans
  • Male
  • Middle Aged
  • Neuropsychological Tests
  • Parkinson Disease / complications*
  • Reference Values
  • Severity of Illness Index