Living with Chronic Illness Scale: Validation in a Type 2 Diabetes Mellitus Population

Background: Worldwide, type 2 diabetes mellitus (T2DM) is one of the most prevalent chronic diseases and one of those producing greatest impact on patients’ day-to-day quality of life. Our study aim is to validate the “Living with Chronic Illness Scale” for a Spanish-speaking T2DM population. Methods: In this observational, international, cross-sectional study, 582 persons with T2DM were recruited in primary health care and outpatient hospital consultations, in Spain and Colombia, during the period from May 2018 to June 2019. The properties analysed were feasibility/acceptability, internal consistency, reliability, precision and (structural) content-construct validity. The COSMIN checklist was used to assess the methodological/psychometric quality of the instrument. Results: The instrument has adequate internal consistency and test retest reliability (Cronbach’s alpha = 0.90; intraclass correlation coecient = 0.96, respectively). In addition, the instrument is accurate (standard error of measurement = 3.34, with values <½SD = 8.52 considered acceptable) and correlates positively with social support (DUFSS) (r s = 0.56), quality of life (WHOQOL) (r s = 0.51-0.30) and satisfaction (SLS-6) (r s = 0.50-0.38). The questionnaire discriminates by the level of severity of the illness (Patient Based Global Impression of Severity Scale), associating lower values with greater severity, and also by male gender. The COSMIN checklist is favourable for all the properties analysed, although some weaknesses are detected for content validity. Conclusions: “Living with T2DM” (LW-T2DM) is a valid, reliable and accurate instrument for use in clinical practice to determine how a person’s life is affected by the presence of diabetes. This instrument correlates well with the associated constructs of social support, quality of life and satisfaction. Additional research is needed to determine how well the questionnaire structure performs when robust factor analysis methods are applied. This macro research to evaluate term (LTC), as In particular, this is study was focused in the validation study of people living with T2DM in a Spanish-speaking population which is part of a range of validation studies out in different LTCs all over the (Spain, South America, UK). term GP: ICC: SEM: standard error of measurement; SD: standard desviation; PRO: Patient Reported Outcome; HF: heart failure, CPOD: chronic obstructive pulmonary disease; TPB: Theory of Planned Behavior, PD: Parkinson Disease; ISPOR: International Society for Pharmacoeconomics and Outcomes Research; PAID: Problem Areas in Diabetes Scale.

accordance with the steps outlined in Rodgers' evolutionary concept analysis [5], we may consider the goal of "living with chronic illness", which has been de ned as "a complex, dynamic, cyclical and multidimensional process with the nal desired target being to achieve positive living" [6]. Various instruments have been proposed to measure this or other concepts associated with managing chronicity. Some have evaluated speci c constructs: for instance, the Minnesota Living with Heart Failure Questionnaire (MLHFQ) [7] and the Living with Chronic Obstructive Pulmonary Disease Questionnaire (LCOPD) [8] both address the patient's quality of life; the Chronic Pain Acceptance Questionnaire (CPAQ) [9] focuses on acceptance of the process; Brief-COPE [10] considers how the patient copes with the situation. Other considerations are taken into account in the Diabetes Self-Management Questionnaire (DSMQ) [11] and the Psychosocial Adjustment to Illness Scale (PAIS) [12]. However, none of these approaches are based on a perspective that is su ciently wide ranging to measure this phenomenon in all its complexity [13].
However, one recently-developed scale addresses the concept of "living with chronic illness", incorporating a broad spectrum of attributes, including acceptance, coping, self-management, integration and adaptation [6]. This scale, derived from the questionnaire "Living with Chronic Illness" (in Spanish, EC-PC) includes 26 items spanning the above-mentioned dimensions. The EC-PC scale has been validated in a population with Parkinson's disease and has adequate psychometric properties [14]. Its acceptability was later evaluated in a pilot study for other populations (with T2DM, heart failure -HF-, chronic obstructive pulmonary disease -CPOD-or osteoarthritis), which showed that the instrument was viable and presented acceptable preliminary levels of validity [15]. The validation of this instrument for persons with T2DM will make it possible to identify the factors that determine whether a patient is living more or less acceptably with the disease, thus providing clinicians with valuable information enabling them to apply focused interventions.

Design
An observational, international and cross-sectional study (one point-in-time evaluation, with retest) was carried out. This study is part of a macro research project with the general aim of achieving an unique and international self-reported scale to evaluate the process of living with one or more than one long term condition (LTC), as T2DM, rheumatoid and osteoarthritis, chronic kidney disease, chronic obstructive pulmonary disease, chronic heart failure, high blood pressure, and Parkinson's disease. In particular, this is study was focused in the validation study of people living with T2DM in a Spanish-speaking population which is part of a range of validation studies carried out in different LTCs all over the word (Spain, South America, UK).
Sample, sampling and sample size A consecutive cases sampling [16,17] was applied to participant identi cation.
The sample was composed by people living with T2DM in primary health care and outpatient hospital consultations from Spain and Colombia. Inclusion criteria were a) patients with T2DM diagnosis made by an endocrinology or General Practitioner (GP) or a specialist in internal medicine, in any stage of the disease and treatment; b) Colombian or Spanish nationality; c) able to read and understand properly the questionnaires; and d) non-hospitalized patient at the moment of the study. Exclusion criteria were a) patients with cognitive deterioration, acute disorder and/or pharmacological effects that potentially could impact on the objective of the study; and b) refusal to participate in the study.
Sample size was calculated according to international criteria [18] following the highest and more exigent rule of 10 participants per item of the scale and country. In this way, considering that the EC-PC questionnaire  (hereinafter Living with type 2 Diabetes: LW-T2DM) is a 26-item scale, a minimum sample size of between 260 people living with T2DM per country was estimated. Moreover, in addition to this rule, a statistical analysis was carried out previous data collection to formally calculate sample size. Sample size estimation was based on consideration of con rmatory factor analysis and convergent validity. For the latter, sample size was based on assuming a correlation of 0 (worst-case scenario in statistical terms), a sample of size 267 people with T2DM ensured a 95% con dence interval no wider than +/-0.12.

Instruments
A sociodemographic questionnaire was used to collect personal data of the patient living with T2DM related to gender, age, marital status, educational level and employment situation. Besides, T2DM related questionnaire was used in order to know age of diagnosis, disease duration, and type and duration of treatment for T2DM. As in other validation studies carried out in Spain and UK [14] in addition to sociodemographic and disease related data, the following self-reported scales were also collected: LW-T2DM [15] scale focused to measure living with LTC. It is 26 items distributed in the following 5 dimensions: acceptance (4 items), coping (7 items), self-management (4 items), integration (5 items) and adjustment (6 items). It is a ve-point Likert-scale ranging from 0 (nothing/never) to 4 (much/always) (except for the "acceptance dimension", in which the score is reversed). The nal score ranges from 0 to 104 (higher scores better living with the LTC). The instrument is available as additional le 1 in spanish and english language.
The Duke-UNC Functional Social Support Questionnaire (DUFSS) [19,20] was used to evaluate social support of the patients from their perspective. It is an 8-items that evaluates different dimensions of social support as con dant, affective and instrumental support. The score for each item varies from 1 (much less than I would like) to 5 (as much as I would like).
The World Health Organization Quality of Life Instrument-Brief (WHOQOL-BREF) [21] was used to measure the quality of life of people living with T2DM. The WHOQOL-BREF is comprised by 24-items that evaluates physical health, psychological health, social relationships, and environment. Item response options range from 1 (very dissatis ed) to 5 (very satis ed/very good quality of life).
The modi ed version of the Satisfaction with Life Scale [22] is an instrument to evaluate satisfaction overall with life (item 1) and in regard to other ve areas: physical, psychological wellbeing, social relations, leisure, and nancial situation. Each item scores from 0 (unsatis ed) to 10 (totally satis ed).
The Patient Based Global Impression of Severity Scale (PGIS) [23] was used to evaluate the patient global impression of severity of the T2DM. It is a six-point Likert-scale ranging from 0 (not ill at all) to 5 (extremely ill) according to the patient.
For this validation study, the Spanish version of the scales was used.

Data collection
Data collection was carried out between May 2018 and June 2019. The potential participants (people living with T2DM) lled in the scales during the consultation with the endocrinology, GP, nurse specialist or primary care nurse. To ensure homogeneity and reproducibility of the procedure of data collection, a standardized protocol was established with the following steps: explaining the research study; asking about doubts; reading out load instructions of the scales and its answer options; writing a check mark in the answer chosen by the patient; reading out load instructions of self-reported scales and giving participants time to complete it. The completion of the instruments took an average of 30-40 minutes.
Data collection related to test-retest was also protocolized to minimize potential random errors.
Patients were asked to answer a second time to the LW-T2DM at home. The LW-T2DM was in an envelope with seal and the research postal direction in order to complete the questionnaire and send it in an easy and free way to the researchers. A minimum sample of 50 subjects and a time span of 7 to 10 days for the retest was planned.

Data analysis
Descriptive statistics (central tendency measures, proportions) were used to determine the sociodemographic and T2DM characteristics. Main data were ordinal or did not t normal distribution. Therefore, non-parametric statistics were used.
The following psychometric properties were tested in this LW-T2DM validation study: Feasibility and acceptability. Quality of data was considered satisfactory if 95% of the data were computable. The limit for missing data was < 5% [24]. Floor and ceiling effect were deemed acceptable if they were < 15% [25] and the skewness was expected between − 1 to + 1 [26].
Precision was estimated by means of the standard error of measurement (SEM = SD * √ [1-r xx ]), where SD was standard deviation and r xx the reliability coe cient. A SEM value < ½SD was used as criterion of acceptable precision [33,34].
Construct validity. For convergent validity, a moderate (r s ≥ 0.35-0.50) or strong relationship (r s > 0.50) [35] was hypothesized between LW-T2DM and DUFSS, SLS-6, and WHOQOL-BREF, and a weak/moderate association with other variables of the study, as age, T2DM duration or treatment. Spearman rank correlation coe cients were obtained to this purpose.
Internal validity, de ned as the inter-correlations between the LW-T2DM dimensions (standard, r s = 0.30-0.70) [30] and known-groups validity for gender, treatment and PGIS scores were determined. Mann-Whitney and Kruskal-Wallis tests were used for groups comparison.

COSMIN assessment
The COSMIN Checklist (COnsensus-based Standars for the selection of health Measurement INstruments) and its extension for content validity, were used for assessing the nal measurement properties of the instrument and the methodology [36,37].
Results 582 people living with T2DM from Spain and Colombia were included in this rst validation study, where the 52.6% of the sample were female with an average age of 64.15 (SD = 2.18). The 57.5% were married, the 60.3% present primary studies showing a basic educational level and the 30% were actively working full time at the moment of the study. The mean age of T2DM duration was 10.25 (SD = 9.51) and the mean age with treatment 7.86 (SD = 7.80) ( Table 1). According to analysed psychometric properties, and in particular results related to data quality showed 6 missing data. More concretely, there were 2 missing data in Domain 2. Coping, one missing data in Domain 3. Selfmanagement, and 3 missing data in Domain 5. Adjustment. According to acceptability, oor and ceiling effects for the total score ranged between 0.2% and 1.7% respectively. Domains and total score of the LW-T2DM did not showed skewness.
Results related to internal consistency of the LW-T2DM showed that Cronbach's alpha was 0.90 for the total scale and for the domains ranged between 0.71 (Domain 3. Self-management) and 0.82 (Domains 1. Acceptance and 5. Adjustment). Item homogeneity ranged between 0.36 (Domain 4. Integration) and 0.53 (Domain 1. Acceptance). As it is showed in Table 2, all corrected item-total correlations were higher than established standard value. According to the precision of the LW-T2DM, SEM was 3.34 (<½SD = 8.52) for the total score of the scale and for the domains range from 0.92 to 1.52 (see Table 3).  Finally, results related to construct validity were the following. Related to convergent validity, the LW-T2DM presented strong relationship with DUFSS (r s =0.56), with SLS-6 (r s =0.50) and with Domain 2 of WHOQOL-BREF related to psychological health of the person (r s =0.51). Besides, the LW-T2DM presented moderate correlations with all items of the SLS-6 and Domains 3 and 4 of the WHOQOL-BREF related to social relationships and environment, respectively. Weak correlation was found with T2DM duration and physical health of the patient (see Table 3). According to internal validity, domains inter-correlated from 0.09 (Acceptance with Coping) to 0.65 (Selfmanagement and Integration). See Table 3 for further detail. In relation to known-group validity, results showed that total scores were signi cantly different for gender (higher in women) and for PGIS (see Table 4).

Discussion
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 de ne the concept of "living with chronic illness". For this purpose, an in-depth conceptual analysis was rst performed [6], reviewing the literature on this question and making use of Rodgers' method of evolutionary concept analysis [5]. 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 [15]. Many experts in the eld consider this practice essential to ensure that the questionnaire items really address the construct that is to be measured [38].
In the present study, the non-response rate was less than 5% for all dimensions; there was no oor 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 [25].
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 [39]. Similarly, the questionnaire presents high reliability in the sub-sample selected for the retest, comfortably surpassing the minimum levels recommended (ICC > 0.70) [39] despite its signi cant extension, with 26 items. These ndings 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 [40]. 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 [14], 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 signi cant differences according to the severity of the condition; thus, patients who are assigned higher scores (re ecting 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 nding differs from that produced by the pilot study, although this preliminary work included a population with other chronic diseases (COPD, HF or osteoarthritis) [15]. Other studies have shown that women with T2DM are at greater risk than men of psychosocial maladjustment, a poorer cardiovascular pro le and/or non-compliance with treatment goals [41,42]. These outcomes are not consistent with our ndings 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-e cacy [43], 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) [46]. 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, re ecting how a person with T2DM lives with the disease and thus allowing professionals to focus on the most troublesome aspects. This role is especially signi cant 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 su ciently individualised [47]. 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 [48]. If these factors were equally in uential with respect to T2DM, we would be facing a scenario in which social factors exerted signi cant in uence 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 [49]. While LW-T2DM is based on an important conceptual analysis of published research, the ndings 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) [50] and the Diabetes Empowerment Scale [51]. 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.

Conclusions
LW-T2DM is a valid, reliable and precise instrument for assessing the question of living with T2DM. Additional research is needed to identify the factors that speci cally impact on the concept of "living with" this disease. In addition, more extensive analyses should be made of the construct under study, by robust methods such as evaluating its factor structure by means of structural equations. voluntary way in the study without any compensation for this. after receiving the pertinent verbal and written information. All data and information related to the participant's identity was handled in full con dential way throughout the research process by the principal investigator.

Consent for publication
Not applicable Availability of data and materials The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests Authors' contributions JC-B, CR-B and LA have made substantial contribution to the design of the work, conception, acquisition, analysis and interpretation of data and drafted the work. He has also approved the submitted version and agreed both to be personally accountable for the author's own contributions and to ensure that questions related to the accuracy or integrity of any part of the work. DP-M, ET, GC, AF-R, SC, and MA-G have done the acquisition of the data, have approved the submitted version and have agreed both to be personally accountable for the author's own contributions and to ensure that questions related to the accuracy or integrity of any part of the work.  Additionalmaterial.docx