This study was conducted to assess the reliability and validity of ICECAP-A in Chinese T2DM patients and explore the correlations of the ICECAP-A with the EQ-5D-3L. Despite cross-cultural differences between countries, our study suggested that the Chinese version of the ICECAP-A was able to measure QoL of T2DM in China. The results provided supporting evidence for the reliability and validity of the adapted version of the ICECAP-A.
4.1 Main Findings
The statistic results of the T2DM patients on two instruments were reported mean values of capability score and HRQol score, and both values were higher than those in the general population [11] and other diseases population (e.g. Asthma, Cancer, Hearing, Arthritis, Heart disease) [22]. The capability score and HRQol score were influenced by some factors, such as disease and age [16, 23–26]. In terms of the effect of disease, the lower score might be due to disease, but on the other hand, the score may not be significantly lower or higher due to the population's adaptation to disease; in terms of the effect of age, some studies show a positive or negative effect on the score with increasing age, with the reasons that the increased impact of disease with age, especially in the elderly population, and the increased adaptability of the population with age [16, 27]. Across the five dimensions in ICECAP-A, the T2DM patients had the least number of people at the full capability level in the Achievement dimension and the most number of people at the full capability level in the Autonomy dimension, consistent with the results of the Chinese general population [11].
In terms of reliability, the Cronbach’s alpha coefficient was 0.72 for the ICECAP-A and EQ-5D-3L, which was lower than the previous results in the Chinese general population (0.80) [11], German T2DM patients (0.83), and English T2DM patients (0.86) [16]. However, the results of the Cronbach’s alpha coefficient for omitting each item showed that the internal consistency of the questionnaire was high.
Overall, the dimensions of the two scales were weakly to moderately correlated (0.2–0.6), which is consistent with the general population [11, 17] and women with irritative lower urinary tract symptoms [15]. However, in significant contrast to these studies, we also observed weak negative correlations among ICECAP-A, EQ-5D-3L, and EQ-VAS. The possible reasons are as follows: Among the five dimensions of EQ-5D-3L, Mobility, Self-care, Physical activities, and Pain/discomfort are more related to physical health, and among these dimensions, the Chinese population perceives that the three dimensions of Mobility, Self-care, and Physical activities had a significantly greater impact on health-related quality of life than the Pain/discomfort dimension [28], the problems appearing in the dimensions of Mobility, Self-care, and Usual activities will not only affect patient’s QoL, but will also significantly affect that family members engage in a multitude of essential activities for patients, some of which need time, energy, material and physical demands, and if such health problems persist over time, they can also significantly reduce the well-being of the entire family, and thus negatively affect the patient's own sense of Stability, Attachment, Autonomy, and Enjoyment, and appear problems on the Pain/discomfort dimension, which may only be considered relatively minor health problems (especially discomfort), so family members engage in more emotional and psychological support. Whereas more than 80% of the respondents in this study were over 55 years old and 55% were older than 65 years, in China, most older people live with their children, and when they experience mild discomfort such as Pain/discomfort, their families and children can give them more emotional and psychological family supports, therefore, these respondents may experience higher capability on the dimensions of Stability, Attachment, Autonomy, and Enjoyment. It was also observed in the study that the Pain/discomfort dimension was positively correlated with the Achievement dimension, which was closely related to respondents' capability. EQ-VAS was negatively correlated with the Autonomy dimension and the correlation coefficient exceeded 0.2, possibly because the Autonomy dimension represented the independent of the respondent's capability, a larger proportion of the respondents in this study were older, and this population may need more family support, and therefore its higher capability in terms of independence did not necessarily mean the overall QoL was higher (EQ-VAS score was higher). The correlation coefficients of ICECAP-A with EQ-5D-3L and EQ-VAS were lower than those in knee pain [18] and irritative lower urinary tract symptoms [15], but consistent with these studies, ICECAP-A was weakly correlated with EQ-5D-3L than with EQ-VAS [29].
In terms of discriminative validity, there were statistically significant associations between measured capability and age, marital status, work status, insurance, income source, and HbA1c, while there were only significant associations between measured HRQol and marital status and number of complications, but both the two instruments were significant associations with self-reported health status and self-reported happiness. However, based on the results in regression, the independent variables with statistically significant coefficients in ICECAP-A were similar to EQ-VAS.
In terms of construct validity, although the Anxiety/depressed dimension had the highest correlation with the four dimensions in the ICECAP-A, the Anxiety/depressed dimension was still loaded with factor 1 with the other four dimensions of the EQ-5D-3L in the factor analysis, which was different with the general population [11, 17] and patients with knee pain [18], where the Anxiety/depressed dimension was loaded with another factor with the five dimensions of the ICECAP-A.
4.2 Limitations and future direction
This study has a few limitations that are worthy of discussion. First, the ICECAP-A instrument was not included in the previous waves’ questionnaires and therefore test-retest reliability could not be assessed in this study. Further investigation can be undertaken to use longitudinal data to test the correlation of ICECAP-A changes and diabetes clinical outcome changes. Second, the sample size for this study is small and concentrated in patients who are older than 65-years old. Thus, the conclusion should be cautious when it is promoted and applied to T2DM patients nationwide. Further studies with other chronic patients and compared to the ICECAP-O instrument are needed to add evidence to the international literature on the validity and use of the ICECAP-A. Third, the ICECAP-A tariff score is based on the UK value set, and studies have shown that the numerical differences in the EQ-5D scores obtained from the conversion tables of different countries are statistically significant [30-32]. For this reason, it is necessary to develop a Chinese ICECAP-A value set to conduct economic evaluation. Finally, a self-reported health survey may suffer reporting heterogeneity [33], different populations have different understandings of the meaning of the same concept, e.g., women consider more emotional aspects of health than men when making self-assessment of overall health [34]; even if there is a consistent understanding of the meaning of the measured health concept, different groups may have different judgments about the actual level represented by a uniform response option [35]. This was not explored in the current work but could however be investigated by using anchoring vignette method to examine the effects of response heterogeneity in the self-reported capability survey. In this study, when the ICECAP-A scale was validated in the T2DM population, there were differences in the correlation with the EQ-5D-3L scale and factor loading with the general population and other disease populations and may be partly due to heterogeneity of disease or population. Therefore, studies on the measured properties of ICECAP-A in other disease populations could be conducted in the future.