Translation, cross-cultural adaptation and validation of the questionnaire from original English version into Spanish was carried out using the methodology proposed by Ramada Rodilla et al (10).
Participants
A prospective study with 100 out patients (cohort 1, n=20; cohort 2, n=80) was carried out. Patients were recruited from the outpatient clinic of Angiology and Vascular Surgery Departments from two University Hospitals in Madrid, Spain (Jiménez Díaz Foundation University Hospital and La Paz University Hospital). Eligibility criteria included: 1) patients over 18 years of age, 2) from both genders, 3) with a diagnosis of PAD (intermittent claudication or critical limb ischemia), 4) whose first language was Spanish, 5) without cognitive impairment or other alteration that could difficult understanding of the questionnaire, and 6) who signed the Informed Consent Form. Patient relevant clinical information, including gender, age, employment status, PAD risk factors and stage were registered in a specific case report form in a pseudonymized fashion.
Translation and Cross-cultural adaptation of VascuQol-6 questionnaire from English to Spanish
Direct translation: Two bilingual translators (MGA, BSJ), whose native language was Spanish, independently carried out a conceptual translation into Spanish of the original English version. One of the translators knew the objectives and concepts considered in the questionnaire, and had previous experience in technical translation of texts, while the other translator had no prior knowledge of the questionnaire and was unaware of the objectives of the study.
Synthesis version: The two translators compared their individual translations and agreed on the final result. A process report was written together with the preliminary VQ-6 Spanish Version questionnaire (Version 1.0). That questionnaire was administered to four patients in order to have an approach of the understandability of the tool.
Back translation: Preliminary VQ-6 Spanish Version (Version 1.0) was back-translated into English by two native English language translators (PF, OS) in order to warrant that the concepts of the original version had been preserved.
Consolidation by Committee of Experts: The four authors of the translation and back translation, together with an expert in methodology and a health professional (LLJ), confirmed the semantic and idiomatic equivalence of the questionnaire that had been back-translated into English with the Preliminary VQ-6 Spanish Version (Version 1.0). The final version was renamed as "VQ-6 Spanish Version" (Version 2.0).
Test / Applicability / Feasibility of VascuQol-6 Spanish Version: The scope of this step was to study whether the VQ-6 Spanish Version (Version 2.0) was understandable for a bigger sample of the population to whom the questionnaire is directed. Considering the type of evaluation and following the methodological recommendations (11), the sample size was established in 20 patients (cohort 1). Participants completed the VQ-6 Spanish Version and were asked the following questions “Are the questions easy to understand? Do you find them relevant for your condition? Do you have any suggestions?”
Validation of the VascuQol-6 Spanish Version
In order to assess the degree in which the VQ-6 Spanish Version was capable of measuring without bias (i.e. reliability of the instrument) (12), reproducibility and internal consistency of the questionnaire was statistically evaluated. The ability of the questionnaire to measure the construct for which it has been designed without bias (19,23) was evaluated through the criterion validity and construct validity.
Re-Test / Reproducibility /Intra-observer reliability
A new sample of patients (cohort 2, n=80) was asked to fill out the VQ-6 Spanish Version (Version 2.0) at two different moments with a 3-4 week interval. This period of time was considered short enough to assure that clinical change had not occurred but long enough to prevent recall of what participants had answered when they filled the questionnaire for the first time. Reproducibility of VQ-6 Spanish Version was assessed through the calculation of the Intraclass Correlation Coefficient (ICC) together with its 95% confidence interval (95% CI). Coefficients > 0.7 represented a good reproducibility (13,14).
Internal consistency
Cronbach’s alpha was used to evaluate the total score as well as each item of the questionnaire by eliminating each one of the questions in order to assess if the elimination of any of these questions affected the internal consistency. A reliable HRQoL measure should center between 0.7 and 0.9 for group comparisons (15,16).
Criterion validity
Defined criterion validity establishes the validity of the questionnaire by comparing it with the gold standard test (12), which in this case was the SF-12 questionnaire (17). SF-12 is a reduced version of the SF-36 questionnaire, easy to apply to assess the functional capacity of people over 14 years of age. It includes eight dimensions: physical role, body pain, mental health, general health, vitality, social function and emotional role. We used version 2 of the tool, in which 50 (with an SD of 10) is taken as the mean of the general population. Values above 50 were interpreted as best, while values below 50 were interpreted as worse than the mean. For each of the items in each dimension, the score ranges from 0 (the worst health for that dimension) to 100 (the best health for that dimension). Patients from cohort 2 also completed the SF-12 questionnaire at baseline and after 3-4 weeks, and the results of both quality of life scales were compared through the Pearson's correlation coefficient, together with the linear regression line. Coefficients >0.7 were considered acceptable (13).
Construct validity
In this study, we evaluated whether the VQ-6 Spanish Version was capable of differentiate intermittent claudication from critical ischemia. Rutherford-Becker (RB) category is used in patients with PAD to classify chronic arterial disease into clinical categories (category 0: asymptomatic; category 1: mild claudication; category 2: moderate claudication; category 3: severe claudication; category 4: pain at rest; category 5: minor tissue loss; category 6; ulcer o gangrene). The specific uniliteral hypothesis (13,14,16) that we proposed was that patients with intermittent claudication (RB categories 1, 2, 3) would have higher scores in VQ-6 Spanish Version, while patients with critical ischemia (RB categories 4, 5 and 6) would have lower scores according to the published data of the original version of VQ-6 (4,5,18).
Statistical analyses
Quantitative variables were described with mean and standard deviation since there were no strong asymmetries in their distribution. Qualitative variables were described by absolute and relative frequencies. Internal consistency was measured by Cronbach’s alpha. The coefficient was calculated for all the items and deleting each of them. To evaluate the intra-observer reliability, the intraclass correlation coefficient between test and retest measures was calculated. Also, a Bland-Altman plot was made to study the differences between test and retest measures. Criterion validity was evaluated by calculating the Pearson’s correlation coefficient between the VQ-6 domains and the SF-12 physical and mental dimensions. Scatter plots were used to visualize the relation between VQ-6 domains and SF-12 physical and mental dimensions. To study the ability of VQ-6 scores to discriminate between patients with claudication and patients with ischemia, a ROC curve was constructed, and its area was calculated. To construct the ROC curve the Leave-one-out cross validation method was used. All statistical analyses were performed using R version 4.0.5 (R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria).