This study shows the ABCC-scale to be a valid and reliable instrument for evaluating the experienced burden of disease for people with COPD, asthma or T2DM. Firstly, the ABCC-scale showed to correlate in at least 75% of the postulated hypotheses, thereby confirming its construct validity. Secondly, the ABCC-scale was in most cases able to differentiate known groups of people with COPD, asthma, and T2DM. Thirdly, the ABCC-scale has adequate internal consistency for the total score and multi-item domains (i.e. physical limitations, feelings/emotions and asthma complaints). Lastly, the ABCC-scale showed to have excellent test-retest reliability.
These results indicate that the ABCC-scale can be used as a valid and reliable scale to measure and evaluate the experienced burden of disease for people with COPD, asthma, or T2DM. People with these chronic conditions can thus identify which domains are most prominent in their experienced burden. The results will be visualised during consultation with the healthcare provider. Based on these results, the healthcare provider and patient can select a domain that is most relevant to be discussed. Using shared decision-making, personalised goals can be formulated, which can help the patient to mitigate the burden of disease. The ability to differentiate known clinical groups enables the caregiver to step into a more detailed conversation regarding that particular domain. Therefore, the ABCC-tool focusses the conversation towards the domains that need attention and the domains that both caregiver and patient would like to discuss.
The results should be reviewed with several notions. First, recruitment bias may have occurred. Upon careful examination of the outcomes of all questionnaires, one may conclude that the participants of this study experienced low levels of burden. The experienced burden ranged roughly from 0 (“never in the past week/month” or “not at all limited”) to 3 (“several times in the past week/month” or “moderately limited”), on a scale from 0 to 6. That means that the validity and reliability may not hold true for people that experience high levels of burden. This may relate to the possible drawbacks of recruiting people from patient advocate groups, which are in general highly educated people, who are well-connected to the patient group (44). Second, the efforts in the recruitment phase eventually led to sample sizes of 65, 62, and 60 for people with COPD, asthma and T2DM respectively. This means that our participant-to-item ratio was roughly four. The sample was thus within recommended sample sizes (8). Third, this study has evaluated the validity and reliability of the same scale for three different conditions, thereby strengthening the assumption of validity and reliability of the generic part of the scale for multiple conditions. Fourth, the ability to differentiate known groups from the literature adds to the relevance of the ABCC-tool for scientific and clinical use.
To our knowledge, this is the first study of a questionnaire that combines the experienced burden of disease for people with COPD, asthma or T2DM into a single questionnaire. The validity and reliability of the ABCC-scale for these conditions separately justify investigation of its psychometric properties for people with multimorbidity. Additionally, in contrast to many other questionnaires, the ABCC-scale largely consists of single-item domains. This means that it suits for brief and efficient clinical application, where more robust questionnaires are simply too time consuming. The results of the current study are in line with the results from the ABCC-tool’s predecessor, the Assessment of Burden of COPD (ABC)-tool (45). Although the content of the ABC-scale was changed while developing the ABCC-scale for multiple chronic conditions, the resulting domains are still valid. The ABCC-scale is able to differentiate people with COPD regarding exacerbation status and an indication of depression. The results of this study justify the use of the ABCC-scale within the ABCC-tool for people with COPD, asthma or T2DM.
This study builds on the development of the ABCC-tool, and facilitates future research in several ways. The conversation is guided by the domain scores of the ABCC-tool. In the current score calculation, all domains are assumed to be equally relevant to the total score. This may not necessarily be the case, and should be studied by for example performing a discrete choice experiment (46, 47). A weighted total score can be used by caregivers to monitor overall progression or deterioration, or for example to compare on a group level. Furthermore, knowledge of the psychometric properties of the ABCC-tool in the single conditions serves as a basis and a prerequisite to study its properties in people with multiple conditions. Lastly, to test the effectiveness of the ABCC-tool and evaluate user experiences upon applying the tool in clinical practice, further research should be performed (48).