Background
Methods
Phase I - qualitative study
Literature review
Focus groups
Phase II - psychometric evaluation of the Revised SCOPA-DC
Study design
Recruitment
Study measures
Statistical analysis
Scoring of the Revised SCOPA-DC
Factorial structure of the Revised SCOPA-DC
Item-level psychometrics
Reliability
Convergent and discriminant validity
Known-groups validity
Measurement of symptom fluctuations
Prediction of off-time
Results
Phase I - qualitative study
Domains identified through literature review
Characteristics of focus groups participants
Content validity of original SCOPA-DC in the U.S. population
Domain elicitation
Changes to original SCOPA-DC
Phase II - psychometric evaluation of the Revised SCOPA-DC
Recruitment
Sample characteristics
N | (%) | ||
---|---|---|---|
Age in years, mean (SD) | 66.3 | (12.5) | |
Gender | Male | 51 | (50.5) |
Education | Less than high school | 6 | (5.9) |
High school | 13 | (12.9) | |
Some college | 41 | (40.6) | |
Bachelor's degree or higher | 41 | (40.6) | |
Race/Ethnicity | White, Non-Hispanic | 89 | (88.1) |
Black, Non-Hispanic | 5 | (5.0) | |
Hispanic | 4 | (4.0) | |
Other | 3 | (2.9) | |
Marital Status | Married | 71 | (70.3) |
Widowed | 6 | (5.9) | |
Divorced/Separated | 13 | (12.9) | |
Never Married/Living with partner | 11 | (10.9) | |
Employment Status | Working - paid employee | 20 | (19.8) |
Working - self-employed | 1 | (1.0) | |
Not working/Retired | 80 | (79.2) | |
Diagnosed with PD | Less than 1 year | 20 | (19.8) |
1 year or more | 81 | (80.2) | |
Number of years, mean (SD) | 7.4 | (5.4) | |
PD Symptoms | Resting tremors | 78 | (77.2) |
Slowed ability to start and continue movements | 41 | (41.0) | |
Rigidity or inability to complete a movement, stiffness | 35 | (35.0) | |
Difficulty with balance or instability | 51 | (51.0) | |
Stooped, forward-leaning posture | 32 | (32.0) | |
Freezing or sudden, brief inability to move the feet | 16 | (16.2) | |
Daily Off-Time | None | 15 | (14.9) |
1-25% of the day | 58 | (57.4) | |
26-100% of the day | 28 | (27.7) | |
Currently taking levodopa | 62 | (61.4) | |
Time taking levodopa | Less than 1 year | 11 | (17.7) |
1 year or more | 51 | (82.3) | |
PDQ-8 Summary Index, mean (SD) | 34.3 | (22.5) | |
WOQ-9 Percentage of Symptoms, mean (SD) | 60.5 | (22.2) | |
SF12v2 - Physical Component Summary, mean (SD) | 38.2 | (10.7) | |
SF12v2 - Mental Component Summary, mean (SD) | 46.0 | (10.5) |
Factorial structure of the Revised SCOPA-DC
Revised SCOPA-DC Item | Two-Factor Model┼
| Three-Factor Model | |||
---|---|---|---|---|---|
Factor 1
|
Factor 2
|
Factor 1
(Mobility)
|
Factor 2
(Physical Functioning)
|
Factor 3
(Psychological Functioning)
| |
01. Walking | 0.82 | 0.79 | |||
02. Changing position | 0.92 | 0.98 | |||
03. Using your hands | 0.68 | 0.74 | |||
04. Uncontrollable movements | - | 0.67 | |||
05. Feelings of exhaustion or fatigue | 0.80 | 0.77 | |||
06. Difficulty concentrating or remembering | 0.76 | 0.95 | |||
07. Feelings of anxiety or panic | 0.59 | 0.75 | |||
08. Unexplained pains | 0.78 | 0.80 | |||
09. Difficulty swallowing | - | - | |||
10. Frequent or urgent urination | 0.69 | 0.72 | |||
11. Sweating too much | 0.58 | 0.56 | |||
CFI/TLI | 0.94/0.91 | 0.97/0.96 | |||
RMSEA (90% confidence interval) | 0.09 (0.05, 0.13) | 0.06 (0.00, 0.10) | |||
SRMR | 0.06 | 0.05 |
Item-level psychometrics
Mobility | Physical Functioning | Psychological Functioning | Cronbach's Alpha | Cronbach's Alpha-item deleted | |
---|---|---|---|---|---|
MOBILITY | 0.87 | ||||
01. Walking |
0.77
| 0.59 | 0.51 |
┼
| |
02. Changing position |
0.77
| 0.67 | 0.55 |
┼
| |
PHYSICAL FUNCTIONING | 0.86 | ||||
03. Using your hands | 0.63 |
0.81
| 0.50 | 0.83 | |
04. Uncontrollable movements | 0.37 |
0.72
| 0.53 | 0.84 | |
05. Feelings of exhaustion or fatigue | 0.61 |
0.83
| 0.65 | 0.83 | |
08. Unexplained pains | 0.63 |
0.74
| 0.56 | 0.82 | |
10. Frequent or urgent urination | 0.43 |
0.77
| 0.56 | 0.83 | |
11. Sweating too much | 0.35 |
0.59
| 0.45 | 0.86 | |
PSYCHOLOGICAL FUNCTIONING | 0.83 | ||||
06. Difficulty concentrating or remembering | 0.55 | 0.69 |
0.72
|
┼
| |
07. Feelings of anxiety or panic | 0.47 | 0.56 |
0.72
|
┼
| |
Model Based Reliability | 0.88 | 0.87 | 0.86 |
Reliability
Convergent and discriminant validity
Convergent/Discriminant Validity (Spearman Correlation Coefficients) | Known-Groups Validity Mean (SD) | |||||||
---|---|---|---|---|---|---|---|---|
HRQOL Measures
|
Baseline Off-Time
|
Disease Duration
| ||||||
Revised SCOPA-DC Subscale | PDQ8-SI | WOQ-9 Percentage of Symptoms | SF-12 PCS | SF-12 MCS | Absence of off-time | Presence of off-time | Up to 5 years | More than 5 years |
Mobility | 0.60†
| 0.45†
| -0.54†
| -0.47†
| 21.7 (17.3)1
| 28.3 (21.7) | 24.9 (21.1)3
| 30.4 (21.1) |
Physical Functioning | 0.58†
| 0.56†
| -0.46†
| -0.60†
| 16.0 (17.6)1
| 21.0 (15.5) | 19.3 (15.6)3
| 20.5 (14.7) |
Psychological Functioning | 0.62†
| 0.48†
| -0.39†
| -0.58†
| 9.2 (20.7)2
| 15.9 (17.8) | 12.4 (17.4)3
| 14.9 (15.8) |
Known-groups validity
Measurement of off-time
Absence of off-time | Presence of off-time | ||||
---|---|---|---|---|---|
N
|
Mean
|
N
|
Mean
|
P-value
| |
Mobility | |||||
CV | 8 | 0.56 | 53 | 0.50 | 0.477 |
SD | 15 | 0.76 | 86 | 0.90 | 0.275 |
Physical Functioning | |||||
CV | 9 | 0.53 | 70 | 0.51 | 0.908 |
SD | 15 | 1.32 | 86 | 1.73 | 0.053 |
Psychological Functioning | |||||
CV | 2 | 0.60 | 31 | 0.60 | * |
SD | 15 | 0.33 | 86 | 0.65 | 0.018 |
Prediction of off-time
Revised SCOPA-DC Subscale | Model Parameter (SE) | Odds Ratio (95% CI) | Chi-Square | P-value | Percentage of Correctly Predicted Observations |
---|---|---|---|---|---|
Mobility | 0.40 (0.07) | 1.49 (1.30-1.71) | 26.80 | < 0.0001 | 69.0% |
Physical Functioning | 0.25 (0.04) | 1.28 (1.19-1.39) | 32.20 | < 0.0001 | 67.7% |
Psychological Functioning | 0.30 (0.07) | 1.35 (1.18-1.55) | 16.76 | < 0.0001 | 69.1% |