Evaluation of life quality of nasopharyngeal carcinoma patients using item response theory

OBJECTIVE:To use item response theory(IRT)to analyze quality of life scale among nasopharyngeal carcinoma patients(QOL-NPC),and understand the psychometric characteristic of QOL-NPC scale.METHODS:The cross-sectional study was used.Totally 387nasopharyngeal carcinoma(NPC)patients were face-to-face interviewed with the QOL-NPC scale.Partial credit model was used to evaluated all items for each dimension(PH,PS,SO and SE dimen-sion).The reliability coefficient of each dimension,the threshold parameter and residual of each item were calculated.Dif-ferential item functioning(DIF)of each item among different gender,age,other diseases were tested.RESULTS:The reli-ability coefficient of all dimensions were greater than 0.80,except SO dimension(0.670).An ordered set of response threshold for almost each item was got,except for the item PH2,PS5,PS6,SO2,SO3,SO5,SE2,SE5,SE6and SE11,and the others were not.The mean threshold parameters were between-0.487and 1.107,with the maximum item SE1(1.107)and the minimum item SE10(-0.487).The standardized residuals which were greater than 2.5included item PH7,PS4,PS5and SE5,the other standardized residuals were samller than 2.5.All the items didn't have uniform DIF or nonuniform DIF.CONCLUSIONS:IRT can provide accurate quantitative analysis on each item.Some items of QOL-NPC wasn't good,therefore it's necessary to improve.