Reliability and validity of the turkish translation of pedsql™ multidimensional Fatigue scale in Duchenne Muscular Dystrophy

Subjects

A total of 71 patients with DMD, whose functional levels were between 1–3 (Level 1: The child is able to walk and climb the stairs, independently; Level 2: The child is able to walk and climb the stairs by using handrails, taking less than 12 seconds; Level 3: The child climbs the stairs slowly, taking more than 12 seconds) according to the Brooke Lower Extremity Functional Classification (BLEFC),10 aged between 5–12 years, who were on corticosteroids for more than 6 months, and who were still ambulant were included in the study with their parents. The children with severe physical and cognitive impairments that block performance and communication during the implementation of questionnaire and functional assessments, and the children with less cooperation were excluded from the study.

Hacettepe University’s Non-invasive Clinical Research Ethics Committee (No: GO 16/331) provided the ethical approval. Children (and their parents) who were directed to the Hacettepe University, Faculty of Physical Therapy and Rehabilitation, Pediatric Neuromuscular Diseases Unit for a routine physical examination after the diagnosis of DMD, signed a written consent form to be included in the study. This study followed the principles of Helsinki Declaration. All of the following assessments performed in this study were implemented approximately at the same time of the day for each child; frequently in the morning, rarely in the midday.

Method. PedsQ™-3.0 Multidimensional Fatigue Scale

The PedsQL-MFS allows to evaluate 2-18 years old pediatric patient population in terms of general symptomatic fatigue, and consists of 18 items. Test items are collected under three subgroups: general fatigue (six items, such as ‘feeling tired’, and ‘feeling too tired to do things that you like to do’), fatigue in sleep/rest (six items, such as ‘feeling tired at morning wake up’, and ‘needing lots of rest’), and cognitive fatigue (six items, such as ‘difficulty paying attention to something’ and ‘difficulty remembering what people tell you’). Clinical experience and studies on chronic pediatric diseases were considered to develop PedsQL-MFS.11,12 It contains questionnaires for the child to evaluate their own fatigue and for parents to evaluate their child’s fatigue. The child and adolescent questionnaires cover the ages 5–7, 8–12, and 13–18, while the young adult questionnaire covers the ages 18–25. For all child, adolescent, young adult, and parental questionnaires, scoring is done on a five-point Likert scale (0 = Never; 1 = Virtually Never; 2 = Sometimes; 3 = Frequently; 4 = Almost Always). The items are scored by linearly reversing the item scores (0=100; 1=75; 2=50; 3=25; 4=0) so that the higher the score, the better the quality of life, which indicates fewer symptoms of fatigue. Thus, a score of 0 indicates great fatigue, and a score of 100 points indicates less fatigue in PedsQL-MFS item scoring.11,13

The permission to perform the Turkish translation of the questionnaire was obtained from the developer of the source scale. The translation steps were as follows;

• I. The English version of the questionnaire was translated into Turkish by 2 persons, independent of each other, that one of them with sufficient knowledge in the field of physiotherapy and rehabilitation.

• II. Then the translations were compared and the differences were evaluated. A common opinion was reached and a single joint translation was created from 2 independent translations.

• III. In the next stage, the Turkish questionnaire was translated back into English independently by 2 native speakers of English who also knew Turkish well, and did not know about the questionnaire.

• IV. The new back-translated questionnaire was compared with the original questionnaire and the differences were evaluated.

• V. After the translation process was over, all translations and reports were evaluated by a committee of experts consisting of methodologists, health experts, language experts and translators involved in the translation. Created questionnaires were corrected by this committee in terms of semantic, idiomatic, experiential, and conceptual equivalence.

• VI. The final version of the questionnaire prepared by the committee was applied to 10 people and it was determined how the questionnaire worked during the application and the unidentified questions were corrected. Thus, the cultural adaptation of the Turkish version of the PedsQL-MFS questionnaire was completed.

Demographic properties including age (years), height (cm), weight (kg), and body mass indexes (BMI; kg/m2), as well as communication information, steroid use, and diagnostic information were recorded. The following functional evaluations were carried out.

The Evaluation of Functional Performance and Ambulation

Individuals participating in the study were subjected to timed performance tests, such as standing from supine position, 10 m walk, and ascending/descending four steps, which were considered to be a significant outcome measure to show functional performance in DMD.14 Another functional performance test—the six-minute walk test (6MWT), which has been used as a gold standard measurement for many clinical studies and which was found valid and reliable for patients with DMD—was also used.15 The distance walked in six minutes was recorded in meters.16

Individuals with DMD—depending on their progressive muscle weakness—tend to modify their movements in order to perform their daily living activities. The North Star Ambulatory Assessment (NSAA) grades daily activities that require ambulation as normal (2 points), modified (1 points), and dependent (0 points). The NSAA is a measure of 17 items that can be completed within 15 minutes, evaluating the skills necessary to maintain ambulatory function, from standing (item 1) to running (item 17). Each item in the NSAA is scored using a three-point scale. The total score is determined by summing the scores of all items, and ranges from 0 (no activity can be achieved) to 34 (all activities are achieved without help).17

Assessment of Quality of Life

The Turkish version of The Pediatric Quality of Life Inventory (PedsQL)3.0-Neuromuscular Module was used in the evaluation of the health-related quality of life of the patients. This scale was found to be valid and reliable in assessing the health-related quality of life of children with neuromuscular diseases between 2 and 18 years of age.18 The PedsQL-3.0 Neuromuscular Module was developed in the form of a parent report for children between the ages of 2 and 4, and in the form of both the child’s personal report and a parent report for children between 5 and 18 years of age. The scale consists of 25 items in 3 categories. Higher scores from the PedsQL-3.0 Neuromuscular Module indicate better health-related quality of life.18

Psychometric and Statistical Analysis

The IBM SPSS Statistics for Windows, Version 21 (Statistical Package for the Social Sciences, IBM Corp., Armonk, N.Y., USA) statistical analysis program was used to assess data obtained from the patients. Descriptive characteristics were identified as minimum, maximum, and mean± standard deviation (X±SD) for the quantitative data, while number (n) and percent (%) values were used for qualitative data. Data was analyzed in terms of normal distribution by using a histogram, the variation coefficient rate, the Skewness-Kurtosis, and Kolmogorov-Smirnov tests. It was determined that the data was not distributing, normally.

Feasibility

Each items’ missing values percentage was examined to determine the feasibility of the PedsQL-MFS Turkish version.19

Internal Consistency Reliability

The standardized Cronbach alpha coefficient was used to detect the internal consistency of the scale. For the Turkish version of PedsQL-MFS, the acceptable internal consistency was decided according to the criteria as Chronbach alpha coefficient >0.7.20

Test-Retest Reliability

The same physiotherapist applied the questionnaire twice to 71 children and their parents with a 2-week interval to test the test-retest reliability of the PedsQL-MFS. The test-retest reliability of the instrument was examined by calculating the intraclass correlation coefficient (ICC), and the ICC values between 0.1-0.3 were accepted as weak, 0.3-0.5 as moderate, and >0.5 as strong.21

Construct Validity

The factor structure of the Turkish version of PedsQL-MFS was investigated by confirmatory factor analysis (CFA). CFA determines if the new instrument presents similar factor solution with the original questionnaire. Thus, to perform analysis; root mean squared error of approximation (RMSEA), goodness-of-fit index (GFI), the chi-squared test (x2), comparative fit index (CFI), adjusted goodness-of-fit index (AGFI), and normed-fit index (NFI) were used. If the degrees of freedom (x2/df) is found <3.0, the GFI, CFI, NFI, and AGFI values are found more than 0.9, and RMSEA is determined <0.1; the instrument is accepted to behave similar with the original instrument.22 Also, a further analysis was performed to evaluate factor structure by using the exploratory factor analysis (EFA). Varimax rotation of the 18 items of the Turkish version of PedsQL-MFS was performed for principal component analysis.

Criterion-Related Validity

Correlations were examined between the scores (total and sub-scores) of the translated questionnaire and functional performance, ambulatory assessment, and quality of life assessment scores using Spearman’s correlation coefficient (rho) to test the validity of the questionnaire in Turkish patients with DMD.

Parent/Child Agreement

The Spearman’s correlation coefficient and ICCs were used for interpretation of agreement between the child’s self-report and parent’s proxy report. The significance levels according to the Spearman’s correlation coefficient were accepted as strong if r=0.7–1.00, moderate if r=0.30–0.70; and weak or insignificant if r=0.05–0.30. Levels were determined to be statistically significant at p < 0.05.