1. Cognitive Data in the Parkinson’s Progression Marker Initiative: Comparison of Normative Data Approaches
Kathryn A. Wyman-Chick, Matthew J. Barrett, Phillip K. Martin, Carol A. Manning, & Scott A. Sperling
University of Virginia Health System – Department of Neurology
Objective
Results
Table 2. Cognitive Impairment prevalence rates for participants with PD in PPMI at baseline using internal scores versus published norms by test
This project examines the impact of different methods of determining normative or standardized cognitive data in the Parkinson’s Progression Markers Initiative (PPMI) dataset.
There were no significant differences in age or education between the healthy control group and the PD group.
Significant differences were found between internal and published norms for LNS, JLO, and semantic fluency. Compared to use of published norms, use of internal norms resulted in significantly lower standardized scores for the LNS, JLO, and semantic fluency (Table 1).
The different methodologies for norming the cognitive data in PPMI resulted in different proportions of individuals identified with cognitive impairment at baseline for delayed recall, working memory, visuospatial ability, and verbal fluency (Table 2).
Impaired %
Unimpaired %
Internal Norms
Published Norms Χ2 df
p-value
HVLT-R Immediate Recall
28.0
31.0
72.0
69.0
0.963 1
.326
HVLT-R Delayed Recall
15.6
32.9
84.4
67.1
34.34
<.001**
LNS
21.1
6.4
78.9
93.6
38.42
< .001**
JLO
8.8
5.2
91.2
94.8
4.10
.043*
Semantic Fluency
22.0
14.5
78.0
85.5
8.13
.004*
SDMT
29.4
26.4
70.6
73.6
.901
.343
Background
Cognition is a frequent outcome measure in Parkinson’s disease (PD) research.
It is important to understand underlying psychometric properties of the cognitive tests included in PPMI and approaches to comparing normative data in order to interpret the results accurately.
Table 1. Comparison between PPMI Internal Norms and Published Age-Normative Data in Participants with Parkinson Disease (n=422)
Raw Scores
M (SD)
Test Performance Based on Internal Norms
Test Performance Based on Published Age-Norms
M(SD) t df
p-value d
HVLT-R Immediate Recall T-Score
24.44 (4.98)
46.43 (11.06)
46.34 (10.99)
-0.22
421
.823
-0.008
HVLT-R Delayed Recall T-Score
8.36 (2.52)
45.99 (10.85)
46.83 (11.75)
1.44
.152
0.074
LNS Scaled Score
10.59 (2.66)
9.67 (3.10)
11.49 (2.68)
37.79
<.001**
0.574
JLO Scaled Score
12.77 (2.13)
9.47 (3.23)
12.79 (2.76)
107.04
0.737
Semantic Fluency T-Score
20.96 (5.34)
47.90 (9.95)
50.79 (9.84)
13.46
0.293
SDMT z-score
41.18 (9.73)
-0.53 (0.92)
-0.49 (0.86)
1.35
.177
0.042
Methods
Notes: PPMI = Parkinson’s Progressive Marker Initiative; HVLT-R = Hopkins Verbal Learning Test Revised Form 1; LNS = Letter Number Sequencing; JLO = Judgment of Line Orientation Odd Numbered Items; SDMT = Symbol Digit Modalities Test Internally Normed z-scores were derived from the mean of the participant score – the group mean of the healthy control group, divided by the standard deviation of the group mean of the healthy control group for each measure. Impaired is defined as less than 1 standard deviation below the normative mean. * p ≤ .05 **p ≤ .001
Data were obtained from PPMI in January Baseline data from 422 participants with Parkinson Disease (PD) were included [Age=61.7(9.7), Education=15.6(3.0)].
Tests included Hopkins Verbal Learning Test-Revised (HVLT-R), Letter Number Sequencing (LNS), Judgment of Line Orientation (JLO), Symbol-Digit Modalities Test (SDMT), and Semantic Fluency.
Internal norms were calculated for each participant using the group mean and standard deviation of the PPMI control group [Age=60.31(11.22), Education=16.04(2.89)].
Paired-sample t-tests were conducted comparing internal norms and published age-norms for each neuropsychological test. Chi-squares were conducted to evaluate the proportion of individuals with impairment (<1 SD below the mean).
Conclusions
Among participants with PD in PPMI, there are differences in standardized cognitive scores depending upon the normative group that is used. The use of internal norms resulted in lower standardized scores than age-norms with the exception of immediate recall.
These differences impacted impairment rates across cognitive measures with the exception of learning and processing speed. Such findings indicate that standardization approaches are not interchangeable.
Selection of appropriate normative comparison groups requires careful consideration, as such decisions can impact both research and clinical interpretations of cognitive data.
Notes: PPMI = Parkinson’s Progressive Marker Initiative; HVLT-R = Hopkins Verbal Learning Test Revised Form 1; LNS = Letter Number Sequencing, JLO = Judgment of Line Orientation Odd Numbered Items; SDMT = Symbol Digit Modalities Test; Internally Normed z-scores were derived from the mean of the participant score – the group mean of the healthy control group, divided by the standard deviation of the group mean of the healthy control group for each measure. T-scores have a mean of 50 with a standard deviation of 10; Scaled Scores have a mean of 10 with a standard deviation of 3; z-scores have a mean of 0 with a standard deviation of 1.
* p ≤ .05 **p ≤ .001
Data used in the preparation of this poster were obtained from the Parkinson’s Progression Markers Initiative (PPMI) database ( For up-to-date information on the study, visit “PPMI – a public-private partnership – is funded by the Michael J. Fox Foundation for Parkinson’s Research and funding partners, including Abbvie, Avid Radiopharmaceuticals, Biogen, Bristol-Myers Squibb, Covance, GE Healthcare, Genetech, GlaskoSmithKline, Lilly, Lundbeck, Merck, Meso Scale Discovery, Pfizer, Piramal, Roche, Sanofi Genzyme, Servier, Teva, and UCB