Table 3 Reliability, scaling success and floor/ceiling effects of the 39 item Parkinson's disease questionnaire.
| Reliability | Scaling success (%)* ‡ | Floor/ceiling effect (%)* § | ||
|---|---|---|---|---|
| Cronbach's alpha* (95% CI) | Test–retest† (95% CI) | |||
| MOB | 0.95 (0.94–0.96) | 0.93 (0.91–0.95) | 75.7 | 11.4/2.5 |
| ADL | 0.89 (0.87–0.91) | 0.93 (0.90–0.95) | 59.5 | 7.9/1.0 |
| EMO | 0.89 (0.87–0.91) | 0.87 (0.82–0.91) | 57.1 | 5.4/0.5 |
| STI | 0.85 (0.81–0.88) | 0.85 (0.79–0.89) | 78.6 | 20.3/0.5 |
| SOC | 0.74 (0.66–0.81) | 0.76 (0.66–0.83) | 57.1 | 35.6/0¶ |
| COG | 0.74 (0.67–0.79) | 0.86 (0.81–0.90) | 21.4 | 6.9/0** |
| COM | 0.87 (0.83–0.90) | 0.86 (0.81–0.90) | 61.9 | 24.3/0.5 |
| BOD | 0.72 (0.65–0.78) | 0.79 (0.72–0.85) | 38.1 | 7.9/0.5 |
ADL, activities of daily living; BOD, bodily discomfort; COG, cognitions; COM, communication; EMO, emotional well being; MOB, mobility; SOC, social support; STI, stigma.
*From first administration.
†One way random intraclass correlation calculated from scores of patients completing both administrations (2 weeks apart) themselves and reporting unchanged health at second administration (n = 137).
‡Percentage of occasions when items correlated significantly stronger with their proposed scale than with other scales.
§Percentage of sample scoring 0 (floor) and 100 (ceiling).
¶Maximum observed score for SOC was 67.67.
**Maximum observed score for COG was 81.25.