Background
Health-related quality of life refers to one's perception and subjective appraisal of his/her health and well-being within a cultural context [
1]. According to the World Health Organization [
2], health is not just the absence of disorder and weakness, but the presence of physical, mental, and social well-being. Given these definitions, health encompasses well-being in different domains of functioning and quality of life includes well-being in those domains.
Health-related quality of life has been recognized as an important outcome measure in health care services and clinical decisions. There are various measures for assessing health-related quality of life and one of these measures is the Pediatric Quality of Life Inventory, Version 4.0 (PedsQL 4.0) [
3]. The PedsQL 4.0 is a multidimensional instrument measuring physical, emotional, social, and school functioning that has been translated into numerous languages. This scale consists of child self-report forms for ages 5–7, 8–12, and 13–18 years and parent proxy-report forms for ages 2–4 (toddler), 5–7 (young child), 8–12 (child), and 13–18 (adolescent) [
4]. The Persian version of the PedsQL 4.0 has been psychometrically evaluated in several studies on healthy and patient samples of Iranian children and adolescents [
5‐
9]. Among these studies, one study [
5] used a sample of children and adolescents diagnosed with Type 1 Diabetes and their parents. The sample in two studies [
6,
7] included healthy and chronically ill children and their parents. Participants in one study [
8] consisted of a group of children with attention-deficit/hyperactivity disorder (ADHD) and their parents and a school-based control group with their parents. The sample of one study [
9] consisted of school children and their parents. While these studies make important contributions, to our knowledge, only one study [
7] has assessed the psychometric properties of the Persian self-report form of the PedsQL 4.0 in adolescents. Moreover, no previous study has examined the convergent validity of the PedsQL 4.0 in Iranian adolescents. Additionally, only one study [
7] has assessed and compared the PedsQL 4.0 scores between male and female adolescents ages 13–18 and no study has addressed the age differences in PedsQL 4.0 scores in Iranian adolescents. In Amiri et al. [
7], the PedsQL 4.0 self-report form showed construct validity and good internal consistency for the subscales (r = 0.68 to 0.78) and for the total scale (r = 0.88). However, convergent validity, test–retest-reliability, and age differences in the PedsQL 4.0 were not assessed. There is a need for studies to more fully examine the psychometric properties of the Persian self-report form of the PedsQL 4.0 in adolescents to improve real-world assessment in clinical and school settings.
The first aim of this study is to assess the validity and reliability of the Persian self-report form of the PedsQL 4.0 in a healthy sample of Iranian adolescents. The second aim of this study is to investigate the effects of gender and age on the PedsQL 4.0 scores. Given the finding that among Iranian adolescents, males have better quality of life than females in the physical and emotional subscales, and total scale of the PedsQL 4.0 [
7], we hypothesized that males will show better quality of life in physical functioning, emotional functioning, and total scale of the PedsQL 4.0.
Discussion
This study assessed the psychometric properties of the Persian version of the PedsQL 4.0 self-report form in Iranian adolescents ages 12–17. The gender and age effects on the PedsQL 4.0 scores were examined. Internal consistency was good to excellent—across both methods of measurement (i.e., Cronbach’s alpha coefficient and McDonald’s omega)—for the subscales and total scale of the PedsQL 4.0. Internal consistencies in this study are similar to the results in Varni, Burwinkle, Seid, and Skarr’s study [
34] and higher than in another study [
7] in Iranian adolescents with a similar age (13–18 years) to our sample. In this study, we also assessed test–retest reliability, convergent validity of the PedsQL 4.0 with a measure of performance in functional domains of life (i.e., WFIRS-S), and the age differences in the PedsQL 4.0 scores—these outcomes have not been examined in previous studies of a Persian-speaking sample and are discussed in greater detail below.
Descriptive investigation of the PedsQL 4.0 items showed that the mean score for most items was close to 80 or above this score. All items showed a negative skewness. These findings show that the participants normally report no major problem in most items of the PedsQL 4.0. These results could be expected in healthy school-based samples and are consistent with the results of previous studies with similar samples [
7,
24].
This is the first study reporting the test–retest reliability of the PedsQL 4.0 specifically in an Iranian sample of adolescents ages 12–17 years. Test–retest reliability was 0.87 for the total scale and psychosocial health and between 0.74 and 0.88 for the subscales. In a study of Iranian children and adolescents ages 8–18 years, test–retest reliability of the self-report form of the PedsQL 4.0 was 0.87 for the total scale and 0.71 to 0.80 for the subscales [
9]. The difference between the results of test–retest reliability for the subscales of the PedsQL 4.0 in the current study and the results of Pakpour et al.’s study [
9] might be explained by the age difference between the sample of two studies.
The current study is the first to assess the convergent validity of the PedsQL 4.0 with another measure in Iranian adolescents. Correlation between the psychosocial health score of the PedsQL 4.0 and functional impairment on the WFIRS-S was negative and high. The correlation between physical functioning and functional impairment was negative and moderate. The stronger correlation of functional impairment with psychosocial health score than with physical functioning reflects more overlap between the PedsQL 4.0 emotional, social, and school functioning subscales with the WFIRS-S content.
The findings of CFA showed that the fit of the four-factor structure of the PedsQL 4.0 was mediocre according to the RMSEA and poor based on CFI. This finding shows that the four-factor model of the PedsQL 4.0 was not fully supported by the CFA indices. The four-factor structure of the PedsQL 4.0 was confirmed in Kook and Varni’s [
24] study in which a larger sample of children with a broader age range (8–18 years) was used in comparison to our study. The results of Varni et al.’s study [
35] showed that the four-factor model of the PedsQL 4.0 was acceptable but the five-factor model including physical, emotional, social, school, and missed school factors indicated a marginally superior fit relative to the four-factor model.
The results of the IRT analysis showed that all items of the PedsQL 4.0 had good fitness with the scale. The discrimination parameter indicated that most items of the PedsQL 4.0 were highly discriminating (a = 1.45–3.02) [
36]. Among the PedsQL 4.0 items, item 8 of the physical functioning, item 3 of the emotional functioning, item 5 of the social functioning, and item 1 of the school functioning showed the highest discrimination and items 1 and 4 of the physical functioning and items 4 and 5 of the school functioning showed the lowest discrimination. Lower discriminating power for items 4 and 5 of the school functioning was also found in another study by Hill et al. [
37]. Items 4 and 5 assessed the degree to which a respondent misses school because of not feeling well or to go to the doctor/hospital. The events proposed in these items for missing the school are more frequent in populations with chronic disorders [
37] not in healthy individuals that consists our sample. Therefore, these items provided low information and were less precise for measuring quality of life in our sample. The evaluation of the threshold parameter demonstrated that all items of the PedsQL 4.0 were located at the lower half of the latent trait. The evaluation of the information provided by each item of the PedsQL 4.0 and by the total scale indicated that this measure would be more precise and useful for measuring the lower levels of quality of life.
The investigation of gender and age effects on the PedsQL 4.0 scores showed that males perceived their function as better in physical and emotional domains relative to female adolescents. This finding is consistent with studies conducted in other countries [
38‐
40] and with a study on Iranian adolescents [
7]. Higher rated physical functioning in males than females may reflect a gender-based disparity in physical strength. Moreover, lower physical functioning and emotional functioning in females than males may have been caused by gender differences in mood problems. Females are not only more vulnerable to have depression, but also, they are more seriously affected by chronic depression, for example they show lower levels of quality of life when they have chronic depression [
41]. Epidemiological studies have indicated that females report more internalizing problems than males [
42,
43]. Our findings related to gender differences in quality of life can also demonstrate the sensitivity of the PedsQL 4.0 to identify these differences. Our cross-sectional study of age on quality of life showed that older adolescents reported more difficulties in all domains of quality of life relative to adolescents with the lower ages. Adolescence is an intermediate developmental stage between childhood and adulthood, and represents a phase of life involving diverse physical, psychological, and social changes and experiences that could influence health-related quality of life [
44].
Limitations
In this study, health-related quality of life was measured by adolescents’ self-report. Future studies should assess the test–retest reliability of the PedsQL 4.0 in adolescents by using parent proxy-report. In this study, only one measure was used to examine the convergent validity of the PedsQL 4.0. Future studies should consider additional measures to assess the convergent validity of the PedsQL 4.0. Another limitation of our study was that the same reporting source (i.e., self-report) was used for our outcome measures, so greater convergence among measures was expected. It is suggested that future studies consider different reporting source for measuring outcome variables.
Conclusions
The findings of our study showed that the PedsQL 4.0 has acceptable psychometric properties as shown by excellent internal consistency, high test–retest reliability, and negative moderate to strong convergent validity with a functional impairment scale (WFIRS-S). Therefore, it is a reliable and valid scale in measuring health-related quality of life in a healthy sample of Iranian adolescents. The PedsQL 4.0 would be a useful instrument for persons with lower levels of quality of life. Significant gender and age differences in quality of life should be considered as important factors in assessment of quality of life in adolescents. In addition, the four-factor structure of the PedsQL 4.0 was not supported—alternative factor structures (e.g., the PedsQL 4.0 second-order factor model consisting of physical functioning and psychosocial health factors [
24] and the five-factor model including physical, emotional, social, school, and missed school factors of the PedsQL 4.0 [
35]) need to be studied in future research.
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