Using Rasch rating scale model to reassess the psychometric properties of the Persian version of the PedsQLTM 4.0 Generic Core Scales in school children

Peyman Jafari,Seyyed Mohamad Taghi Ayatollahi,Zahra Soltani,Zahra Bagheri

doi:10.1186/1477-7525-10-27

Peyman Jafari, Seyyed Mohamad Taghi Ayatollahi + Show 2 more

Open Access

https://doi.org/10.1186/1477-7525-10-27

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Abstract

BackgroundItem response theory (IRT) is extensively used to develop adaptive instruments of health-related quality of life (HRQoL). However, each IRT model has its own function to estimate item and category parameters, and hence different results may be found using the same response categories with different IRT models. The present study used the Rasch rating scale model (RSM) to examine and reassess the psychometric properties of the Persian version of the PedsQLTM 4.0 Generic Core Scales.MethodsThe PedsQLTM 4.0 Generic Core Scales was completed by 938 Iranian school children and their parents. Convergent, discriminant and construct validity of the instrument were assessed by classical test theory (CTT). The RSM was applied to investigate person and item reliability, item statistics and ordering of response categories.ResultsThe CTT method showed that the scaling success rate for convergent and discriminant validity were 100% in all domains with the exception of physical health in the child self-report. Moreover, confirmatory factor analysis supported a four-factor model similar to its original version. The RSM showed that 22 out of 23 items had acceptable infit and outfit statistics (<1.4, >0.6), person reliabilities were low, item reliabilities were high, and item difficulty ranged from -1.01 to 0.71 and -0.68 to 0.43 for child self-report and parent proxy-report, respectively. Also the RSM showed that successive response categories for all items were not located in the expected order.ConclusionsThis study revealed that, in all domains, the five response categories did not perform adequately. It is not known whether this problem is a function of the meaning of the response choices in the Persian language or an artifact of a mostly healthy population that did not use the full range of the response categories. The response categories should be evaluated in further validation studies, especially in large samples of chronically ill patients.

Highlights

Item response theory (IRT) is extensively used to develop adaptive instruments of health-related quality of life (HRQoL)
In recent years, using IRT models has extensively increased in measuring HRQoL in school children [1,3,6,7,8,9,10,11,12,13,14,15,16]
The categorical confirmatory factor analysis (CCFA) supported the fit of a four-factor model for child self-report, root mean square error of approximation (RMSEA) = 0.059, non-normed fit index (NNFI) = 0.96, root mean square residual (RMR) = 0.069, and comparative fit index (CFI) = 0.97, and parent proxy-report, RMSEA = 0.083, NNFI = 0.95, RMR = 0.08, and CFI = 0.96

Summary

Introduction

Item response theory (IRT) is extensively used to develop adaptive instruments of health-related quality of life (HRQoL). There are two different methods for testing psychometric properties of quality of life (QoL) instruments, including classical test theory (CTT) and item response theory (IRT). Traditional psychometric techniques, called CTT, focus on summated scores, in which require two crucial assumptions including unidimensionality and local independence to estimate the model parameters. They need a huge sample size for acceptable performance [4,5]. The PedsQLTM 4.0 Generic Core Scales (hereinafter referred to as PedsQLTM 4.0) is one of the most popular instruments which measures HRQoL in both healthy and chronically ill children. Langer et al [25] have used differential item functioning analyses (DIF) to assess whether scores have equivalent meaning across healthy children and children with chronic conditions

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