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Journal of Chinese Integrative Medicine ›› 2010, Vol. 8 ›› Issue (2): 121-125.doi: 10.3736/jcim20100205

• Original Clinical Research • Previous Articles     Next Articles

Development of patient-reported outcome scale for myasthenia gravis: A psychometric test

 Xin-lin Chena, Feng-bin Liub, Li Guoc, Xiao-bin Liud   

  1. a Department of Preventive Medicine and Health Statistics, College of Basic Medical Sciences,Guangzhou University of Chinese Medicine, Guangzhou 510407, Guangdong Province, China
    b Department of Gastroenterology, the First Affiliated Hospital, Guangzhou University of Chinese Medicine, Guangzhou 510405,Guangdong Province,China
    c Department of Traditional Chinese Medicine, the Second People5 s Hospital of Liwan District of Guangzhou, Guangzhou 510160,Guangdong Province,China
    d Research Institute of Professor Deng Tietao, Guangzhou University of Chinese Medicine, Guangzhou 510407, Guangdong Province, China
  • Received:2009-07-23 Accepted:2009-12-27 Online:2010-02-20 Published:2010-02-15
  • Contact: Feng-bin LIU


To investigate the scientificity of patient-reported outcome (PRO) scale for myasthenia gravis (MG), which was used to evaluate the clinical effects of traditional Chinese and Western medicine treatment on MG patients. Psychometric performance of the MG-PRO scale was also expected to be evaluated in this study.

A total of 100 MG patients and 100 healthy people were face-to-face interviewed by well-trained investigators, and the data of MG-PRO scale were collected. The classical theory test (CTT) and item response theory (IRT) methods were used to analyze the psychometric performance such as validity, reliability, person separation index (PSI) and differential item functioning (DIF) in the MG-PRO scale.

The results of CTT analysis showed that the split-half reliabilities of the MG-PRO scale and each dimension were greater than 0.7. In the analysis of internal consistency of each dimension, the Cronbach's α was greater than 0.8. Each facet had greater correlation with its dimension than the other dimensions. Four principal components were extracted by exploratory factor analysis, which represented all dimensions of the scale, and the cumulative variance was 55.54%. The scores of each of the 8 facets between MG patients and healthy people were different (P<0.01). The results of IRT showed that the PSI of each model was greater than 0.8, and all items did not have uniform DIF and non-uniform DIF.

The MG-PRO scale reflects the definition and connotation of quality of life and contains special issues of MG patients as well, and shows good reliability (split-half reliability, Cronbach's α), validity (content validity, construct validity, discriminate validity) from the results of CTT, and good psychometric performance from the results of IRT.

Key words: Myasthenia gravis, PRO scale, Reliability and validity, Item response theory, Classical test theory

Table 1

Correlation coefficient between 8 facets of MG-PRO scale and each dimension"

Facet Dimension
Physical symptom 0.960 0.435 0.751 0.541
Physical functioning 0.898 0.429 0.664 0.603
Positive mood 0.371 0.930 0.503 0.463
Negative mood 0.473 0.825 0.663 0.534
Personal relationship 0.747 0.638 0.935 0.705
Social support 0.616 0.488 0.862 0.614
Side effects 0.470 0.495 0.630 0.951
Drug dependence 0.686 0.499 0.730 0.798

Figure 1

Structure of MG-PRO scale"

Table 2

Comparison of scores of 8 facets of MG-PRO scale between MG patients and healthy people ($\bar{x}±s$)"

Facet n Mean score t P
Physical symptom
Healthy people 100 67.26±9.73 6.63 0.000
MG patients 100 62.20±11.64
Physical functioning
Healthy people 100 94.00±3.36 8.55 0.000
MG patients 100 78.13±18.26
Positive mood
Healthy people 100 11.20±2.60 3.87 0.000
MG patients 100 9.55±3.38
Negative mood
Healthy people 100 8.19±1.24 8.72 0.000
MG patients 100 5.99±2.20
Personal relationship
Healthy people 100 17.27±2.79 9.39 0.000
MG patients 100 12.75±3.92
Social support
Healthy people 100 11.60±2.22 9.72 0.000
MG patients 100 8.17±2.75
Side effects
Healthy people 100 7.73±1.73 4.15 0.000
MG patients 100 6.55±2.26
Drug dependence
Healthy people 100 4.96±0.24 20.00 0.000
MG patients 100 2.60±1.15

Figure 2

DIF analysis of item 2 between male and female"

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