The current study confirmed that the Chinese version of WURSS-24-C demonstrated highly acceptable reliability and validity, similar to that found during validation studies of the original English language instrument [10, 11].
Exploratory and confirmatory procedures was used to assess item/domain structure of the WURSS-24-C. This version contained four domains, which was different from the original WURSS-21 with three domains (activity and function, nasal symptom and throat symptom). In the WURSS-21 study, the following items Head congestion, Chest congestion, Feeling tired was in the nasal symptom domain, which might not be suitable. In the WURSS-24-C, these items were included in the new domain defined as Systemic symptoms, which also contained the items for assessment of influenza-like illness, Headache, Body aches and Fever (Fig. 1). CFA then further indicated that individual items of the WURSS-24-C, agreed well with this 4-dimensional structure model, as fit indices met criteria suggested by Hu and Bentler .
As a measure of the reliability of a scale, Cronbach alpha has been widely used since it was developed by Lee Cronbach in 1951. According to Tavakol  and Devellis , the alpha values of 0.8 to 0.9 are excellent, but if a coefficient alpha greater than 0.9, it may suggest redundancies and show that the test length should be shortened. We tested the 4 domains of the WURSS-24-C, and the Cronbach alpha perfectly ranges from 0.849 to 0.882, except for the “activity and function”, which is up to 0.943. Compared with the original version of WURSS-21, for which the value is 0.961, we believe this 9-item dimension might be further reduced or adjusted. Then we tested the reliability of the whole WURSS-24-C and found the value was over 0.90. This result suggested that the WURSS-24 might allow leeway for a shorter version, such as the WURSS-11developed by English-language WURSS researchers .
Convergent validity was evaluated by the Pearson correlation coefficient. According to Colton , correlations ranging from 0.50 to 0.75 are moderate to good; and values greater than 0.75 are considered good to excellent. The WURSS-24-C yielded correlation coefficient was over 0.75 when compared with SF-8 physical. The association was stronger than that between the WURSS-24-C with SF-8 mental, for which the coefficient was − 0.721. The results were similar to that of the original version of the WURSS .
Minimal important difference (MID) refers to the smallest difference in a score that is recognized as worthwhile or important . For clinicians, MID could be used to determine meaningful clinical change in patients. Our results estimated MID for individual items of the WURSS-24-C, which could be considered clinically relevant in patients with URTIs. Compared with the data of the original WURSS-21, the instruments yielded similar MIDs indices, which indicated the WURSS-24-C could be sensitively reflected changes in items.
Strengths of this study include its large sample size, regional representativeness, careful translation of WURSS-24-C using three-step linguistic validation procedure, and high quality statistical analysis. Our study should, nonetheless, be interpreted along with several limitations. First, all participants were from the southern part of China with narrow age range, limiting generalizability. Second, the test-retest reliability and other reliability and validity assessments
were not evaluated in this study. Therefore, participants from a broader range of age groups from other parts of China and additional instruments as for the evaluation might be needed in future studies.