Italian translation, cultural adaptation and validation of the PedsQL™ 3.0 Diabetes Module questionnaire in children with type 1 diabetes and their parents

In the last decade, quality of life (QOL) has emerged as an important health objective in diabetes management, being positively related to degree of metabolic control [[1],[2]]. According to the World Health Organization, health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity [[3]]. Therefore, a health-related quality of life (HRQOL) measurement should include physical, mental and social health aspects, be based on different age patient’s perception, and provide evidence of acceptance and reliability. In the perspectives of the health care provider, HRQOL is increasingly becoming a recognized measure of treatment outcome based on the concept that an illness affects all domains of the patient’s and family’s life. Moreover, according to the FDA Guidelines [[4]], HRQOL measurement by means of validated questionnaires is an essential outcome in clinical research in different settings as in pediatrics for international observational studies and clinical trials [[5]].

Juvenile diabetes management involves young patients and all family members, and can interfere with familiar dynamics and habits, affecting both patients’ and parents’ HRQOL [[1],[2]]. The availability of parent-proxy report scales is essential to obtain complementary information in juvenile diabetes HRQOL matters. As a consequence, several generic and disease-specific instruments to measure HRQOL have been developed and validated in diabetes. The Pediatric Quality of Life Inventory (PedsQL™) is a modular instrument for measuring HRQOL in children and adolescents ages 2 to 18 [[6]]. The PedsQL™4.0 Generic Core Scales are multidimensional child self-report and parent proxy-report scales developed as the generic core measure to be integrated with the PedsQL™ Disease-Specific Modules into a one-measurement system. The PedsQL™4.0 Generic Score Scales distinguish between healthy children and those affected by acute or chronic diseases and provide evidence of good feasibility, reliability and sensitivity to different diseases in several reports [[7]–[9]]. The PedsQL™3.0 Diabetes Module questionnaire has been assessed to measure diabetes-specific QOL dimensions in both children and their parents: either PedsQL™4.0 or PedsQL™3.0 Diabetes Module have been tailored for a broad age range including child self-report for ages 5–18 years, and parents’ proxy-report for their children for ages 2–18 years [[10]]. Recently, feasibility, reliability and validity of the new electronic version of e-PedsQL™ for type 1 and type 2 diabetes has been successfully demonstrated [[11]].

Due to the complex construction of each instrument, these measures cannot be assumed to be invariant to cultural diversity, thus requiring cultural adaptation [[12]], and verification of their psychometric properties [[13]–[15]]. The PedsQL™3.0 Diabetes Module questionnaire has already been translated and validated for many languages although not yet in Italian (see the listing of existing translations available from http://​www.​pedsql.​org/​PedsQL-Translation-Tables.​doc. Accessed February 18, 2014).

The purpose of the present study was the translation, its cultural adaptation and statistical validation of the Italian version of the PedsQL™3.0 Diabetes Module questionnaire for a broad age range including children’s and adolescents’ self-reports for ages 5–18 years, and parents’ proxy-reports for their children for ages 5–18 years from six Italian pediatric centers for diabetes.

The results of the current study showed the reliability and validity of the PedsQL™3.0 Diabetes Module questionnaire in its Italian version after cultural adaptation of the disease-specific HRQOL summary measures, i.e., “Diabetes symptoms”, “Treatments barriers”, “Treatment adherence”, “Worry” and “Communication” in children and adolescents with type 1 diabetes. After an independent forward and backward translation of the validated US English version, the Italian version of PedsQL™3.0 Diabetes Module was tested in 169 Italian children and adolescents with type 1 diabetes aged 5–18 years and 100 parents by trained psychologists in the context of a multicenter observational longitudinal study. Even if complex and time requiring, the translational step-wise algorithm of the validation procedure according to the MAPI Research Trust allowed us to produce an Italian version of PedsQL™3.0 Diabetes Module which sounded user-friendly and easy to understand, culturally adapted for the country where it will be used, and conceptually similar to the original US English version. The main strength of this study was the enrollment of a wide range of children and parents willing to participate from Italian Northern-to-Southern regions at the six ISPED centers with proved experience in pediatric type 1 diabetes management. Therefore, the validating population represented the general Italian population of pediatric patients with type 1 diabetes.

The study aimed at validating the PedsQL™3.0 Diabetes Module questionnaire for use in Italy, rather than describing the QOL of pediatric patients with type 1 diabetes. Thus, the use of convenience sample should not impair our conclusions. Still, further applications of this version of instrument, currently ongoing on larger Italian pediatric population (Study EudraCT No. 201001923710), is warranted to confirm our results.

The psychometric properties of the Italian version may be considered satisfying. The mean scores in the different scales were comparable to those of the original version [[10]], and so were the scales with relevant percentages of ceiling or floor according to the IQOLA project approach [[13]]. In term of feasibility, time required to complete questionnaires was around 10–15 minutes. Items of the PedsQL™3.0 Diabetes Module had minimal missing responses, suggesting that patients and parents were able to provide easily QOL data. Similar observation was reported by Varni who evaluated the PedsQL™ in type 1 and type 2 diabetes [[10]], and in the more recent electronic version [[11]]. The PedsQL™3.0 Diabetes Module item internal consistency (i.e., the percentage of items with Pearson item-scale correlation ≥40%) was satisfied at 89% for the child self-report scales and 100% for the parents’ proxy-report scales. Discriminant validity (i.e., the percentage of items with higher Pearson correlation with other scales than with its own scale) was satisfied at 71% for the child self-report scales and at 82% for the parents’ proxy-report scales, respectively. The internal consistency reliabilities of PedsQL™3.0 Diabetes Module self-report and proxy-report as summary measures satisfied the recommended minimum α-coefficient standard of 0.70 for group comparisons [[13]]. For the items of the child self-report scales, they all were in the 0.60-0.70 range, while for the parents’ proxy-report item scales, “Diabetes symptoms”, “Treatment barriers”, and “Communication” ranged between 0.64-0.69. Strong correlation between the child self-reports and parents’ proxy-reports was showed between the same scales, with the exception of “Treatment adherence”, the evaluation of diabetes symptoms than emotional symptoms being the reason for this objectivity and easiness. The number of test items, item interrelatedness and dimensionality affect the value of alpha [[17]]. Although Cronbach alpha represents the lower bound of the reliability of a measurement instrument, and is a conservative estimate of actual reliability [[18]], scales that did not approach or meet the 0.70 standard should be used only for descriptive analyses.

Test-retest reliability was performed in a two-week interval, which was deemed adequate [[19]], having assumed that fluctuations due to external factors, such as disease and treatment variables, were unlikely and not expected to influence the scale functioning. ICC values among the children ranged from good to excellent except for the “Worry” scale. The ICC values for the parents’ proxy-report were excellent, despite the returned 30-50% of retest questionnaires was not met.

Validity was also assessed through factor validity and clinical/external discriminant validity. A factor analysis (principal components, oblique rotation - oblimin) for determining the items’ scale structure of an instrument along with assessment of items’ conceptual clarity was performed on PedsQL™3.0 Diabetes Module for child self-reports and parent proxy-reports to verify aggregating dimensions. This exploratory multivariate technique allows data reduction, i.e., it reduces the number of variables in an analysis by describing linear combinations of the variables that contain most of the information with (possibly) meaningful interpretation. The coefficients estimated from the linear combinations are called factor loadings. Factors were selected if their eingenvalue was ≥ 1. The variance explained by each factor is the eigenvalue for that factor. Although the original US English version has a five factor structure [[10]], exploratory factor analysis identified 10 factors for child self-reports and 9 factors for parent proxy-reports in our Italian version, as detailed in Table 3. Our findings are consistent with those from studies reporting on the factor structure of the original US English version [[20],[21]], and thus support the psychometric properties of the Italian translation version of the measure. As already reported by Nansel [[20]], parallel parent and child scales did not emerge. The factor structure of the PedsQL™3.0 Diabetes Module did not support the original five-factor scales. As reported by other authors [[21]], the findings indicate that the module is most reliable when used as one scale rather than five sub-scales. The external discriminant validity of the PedsQL™3.0 Diabetes Module summary measures were compared across gender, age, time since diagnosis and HbA1c mean cut off values. Significant differences in the “Treatment adherence” scale and in the “Communication” scale were observed across ages and by time since diagnosis.

This study showed the reliability and validity of the Italian version of the PedsQL™3.0 Diabetes Module questionnaire, that is easy to understand and reduces possible cultural biases to a minimum. Therefore, this module could be used as an outcome measure for diabetes cross-national clinical trials and research.