The aim of this study was to validate the original EC-PC scale for persons with DM, obtaining an instrument (LW-T2DM) to measure how this population lives with the disease, with study outcomes that are useful both for research and clinical practice.
Members of the research team have been working for several years to best define the concept of “living with chronic illness”. For this purpose, an in-depth conceptual analysis was first performed , reviewing the literature on this question and making use of Rodgers’ method of evolutionary concept analysis . Before the psychometric evaluation, the questionnaire was piloted in various populations of persons with at least one chronic disease (including T2DM), to determine its viability and acceptability . Many experts in the field consider this practice essential to ensure that the questionnaire items really address the construct that is to be measured .
In the present study, the non-response rate was less than 5% for all dimensions; there was no floor effect and in relation to the ceiling effect, only the 15% limit was exceeded, and that very slightly, for the “acceptance” dimension. These data suggest that, a priori, the scale provides reasonable acceptability .
LW-T2DM has excellent internal consistency (Cronbach’s alpha = 0.90) both overall and for each dimension, always remaining within the recommended limits, which suggests there is no redundancy in the content of the questions . Similarly, the questionnaire presents high reliability in the sub-sample selected for the retest, comfortably surpassing the minimum levels recommended (ICC > 0.70)  despite its significant extension, with 26 items. These findings preliminarily suggest that LW-T2DM is a parsimonious instrument, measuring the intended aspects of the question with the fewest items possible, a quality that is highly desirable . Finally, the instrument is precise and correlates positively, at least to a moderate degree, with the existence of social support and with each of the subdimensions of the scales measuring satisfaction and quality of life. The correlation data are similar to those reported for the population with Parkinson’s disease , showing that the questionnaire measures these cross-sectional constructs in a similar way in each of these chronic conditions.
Application of the LW-T2DM scale reveals significant differences according to the severity of the condition; thus, patients who are assigned higher scores (reflecting better coexistence with the disease) tend to be those who are less severely affected. Moreover, these scores are generally higher than those obtained by persons with Parkinson’s disease, suggesting that living with T2DM is more tolerable. Differences by gender were also obtained, with higher scores for women. This finding differs from that produced by the pilot study, although this preliminary work included a population with other chronic diseases (COPD, HF or osteoarthritis) . Other studies have shown that women with T2DM are at greater risk than men of psychosocial maladjustment, a poorer cardiovascular profile and/or non-compliance with treatment goals [41, 42]. These outcomes are not consistent with our findings and further research is needed to clarify the question.
From a conceptual standpoint, the LW-T2DM scale has similarities with constructs addressed by other theoretical models. Thus, dimensions such as self-management or coping bear an important relationship with Bandura’s concept of self-efficacy , which is widely used by other instruments in psychosocial approaches to chronic diseases [44, 45]. Other dimensions, such as integration or adaptation, are closely linked to the notion of perceived control, introduced by Ajzen in his Theory of Planned Behaviour (TPB) . The instrument also correlates very reasonably with social support, a concept also introduced in the TPB as the subjective norm (perceptions of the impact of third parties – such as family, friends or healthcare professionals – on whether or not the conduct in question takes place). The use of a conceptual model to underpin the LW-T2DM instrument enables the analyst to explain inductively how events happen and to suggest practical solutions to the problems encountered.
At the clinical level, the value of the instrument lies in its explanatory capacity, reflecting how a person with T2DM lives with the disease and thus allowing professionals to focus on the most troublesome aspects. This role is especially significant because healthcare professionals commonly express frustration at not achieving the expected results from treatment and recommendations. On the other hand, many patients believe their healthcare is not sufficiently individualised . Prior analyses of patients with Parkinson’s disease have shown that social support, followed by satisfaction with life and by socioeconomic status, are the only factors relevant to the patient’s coexistence with the disease . If these factors were equally influential with respect to T2DM, we would be facing a scenario in which social factors exerted significant influence on health conditions and should be taken into account when socio-health policies are designed and applied.
Although the present study has been performed with all possible rigour, it is subject to certain limitations. According to the International Society for Pharmacoeconomics and Outcomes Research (ISPOR), for an instrument to present content validity, it must obtain information derived from what is already known on the subject, from the reference population and from healthcare providers . While LW-T2DM is based on an important conceptual analysis of published research, the findings have not been triangulated with information obtained by qualitative techniques (via focus groups, cognitive interviews, the Delphi method, etc.), as described in the relevant section of the COSMIN checklist (Additional File 2). Furthermore, due to the innovative nature of the concept, LW-T2DM lacks a gold standard with which to verify its criteria validity. However, other instruments have been proposed to evaluate psychosocial aspects of diabetes, such as the Problem Areas in Diabetes (PAID)  and the Diabetes Empowerment Scale . Although the approach they take is different from our own, it might be useful to analyse their possible correlations with LW-T2DM. Finally, due to the intrinsic nature of the present research, the question of sensitivity to change has not been evaluated.