The prevalence of SLE in my country is higher than that in Western countries, and the mortality rate in the past is very high. Nowadays, major breakthroughs have been made in treatment. The 10-year survival rate is greater than 80%, but there is no cure, and patients need long-term medication. Long-term medication and prolonged illness repeatedly cause serious ideological and economic burdens to patients. How to evaluate the changes in the physical and psychological health of SLE patients is particularly important. Foreign countries have developed universal scales and specific scales for SLE patients, and they have been widely used. However, due to differences in cultural ideas and diets at home and abroad, the direct use of foreign scales cannot fully reflect the conditions of patients in my country.
In China, there are few reports on the development of quality of life scales for patients with systemic lupus erythematosus. The research team developed the first version of the Quality of Life Instruments for Chronic Disease- Systemic lupus erythematosus (QLICD-SLE (V1.0)) during 2003–2006, referring to the contents of foreign scales and compares them with the clinical practice of systemic lupus erythematosus. The second version of the system of Quality of Life Instruments for Chronic Disease QLICD has been developed since 2008, and the QLICD-SLE (V2.0) was formed in 2017. At that time, the MCID value is not established for the systemic lupus erythematosus scale.
Therefore, in this study, the MCID value was established by the roc curve method, which further made up for the shortcomings in the actual application of the scale, and facilitated the clinical evaluation of the patient's treatment effect through the change of the scale score.
There are four common methods for calculating MCID values, such as anchor-based method, distribution-based method, etc. In recent years, Due to the shortcomings of traditional methods, Roc curve method, multiple regression method, etc. are proposed. With the combination of illustrating the sensitivity and specificity in the same graph, this can facilitate the statistically interpretation with high accuracy [26, 27]. The anchor-based MCID distribution method were recommended for application in the ROC curve to formulate the MCID in other important PRO instruments such as J.J. Wu et al use ROC curve calculating MCID for work productivity and activity impairment ( WPAI ) questionnaire . In the ROC curve, the cut-off point corresponding to the maximum Youden index has relatively high sensitivity and specificity. Compared with the traditional anchor method and distribution method for formulating MCID values, the ROC curve-based method effectively combines the advantages of the anchor method and the distribution method. Different cut-off values to calculate a range of sensitivity and specificity according to the patients’ respondent in projection of the increments of outcomes is the core of the anchor based methods.
ROC curve-based method takes into account measurement errors and makes full use of the sample size as much as possible. It is believed that the correlation coefficient between the scale score and the anchor item score is greater than 0.3, and the sufficiency of the anchor is strong . In this study, the correlation coefficient between the score of the anchor item and the QLICD-SLE (V2.0) scale before the treatment is 0.43. The anchor item is used as a comprehensive indicator to reflect the overall health of patients with systemic lupus erythematosus. To formulate the minimum clinically significant improvement difference of the QLICD-SLE (V2.0) scale, Patients were divided into three different groups according to the changes in the response of the anchor items before and after treatment.
According to Table 1, the mean value for different groups of patients are: +4.7 (improved group) > + 0.30(no change group)> -3.4(deteriorated group). It implied the grouping of patients based on anchor item was feasible. For easy reference, the negative items in the scale were transformed positively, making the scale score more easily interpreted with the patient's health status. If the treatment is clinically meaningful to the patient, the patient's health will also be improved. After the treatment, the patient's score on the QLICD-SLE (V2.0) scale should be higher than before the treatment, that is, after the treatment. The scale's standardized score minus before treatment should be positive. However, in practical applications, the difference between the post-treatment and pre-treatment scale scores is positive or negative. In this study, the difference was used as the test variable, and the classification based on the anchor item was used as the gold standard to construct the ROC curve.
The MCID of QLICD-SLE (V2.0) is 3.2. The patient's scale score after treatment is at least 3.2 points higher than that before treatment, and the clinical treatment is considered meaningful. Through MCID determination, it is possible to further explore the different treatment methods, which is more effective and other research.
The samples of this study mainly come from the southern cities of Guangdong and Yunnan. The economic situation in southern China is relatively good, and the population flow is relatively large. Selecting patients from the above areas for investigation can reflect the status of patients with lupus erythematosus in the Chinese system to a certain extent. Two independent sample t-tests were used to analyze the scores of patients in Guangdong and Yunnan. The results showed that there is no statistical difference in the scores of patients in the two regions before treatment (t = 1.600, p = 0.111). Considering a 5% loss rate, this part of the study requires 181 patients at least. In fact, the results of this survey are that 428 patients participated in the questionnaire survey.
To sum up, formulating MCID value based on ROC curve as a new method has both advantages and disadvantages. The ROC curve intuitively combines sensitivity with specificity and accurately reflects the specificity and sensitivity of an analytical method. However, in the formulation of MCID, an appropriate anchor needs to be selected as the classification gold standard. In practice, it is difficult to find a very appropriate anchor and different anchors will also produce different results. Some literatures  pointed out that using the data of the entire cohort to construct the ROC curve, the accuracy of formulating the MCID is higher. The MCID value of the QLICD-SLE (V2.0) scale developed in this study is 3.2, which can assist in determining whether the treatment has a clinical effect on SLE patients. However, due to the number of study subjects and the limitations of the survey points, the effectiveness of its promotion and use needs further verification.