Differential item functioning in quality of life measure between children with and without special health-care needs

Measurement invariance and adapted preferences: evidence for the ICECAP-A and WeRFree instruments

BACKGROUND

Self-report instruments are used to evaluate the effect of interventions. However, individuals adapt to adversity. This could result in individuals reporting higher levels of well-being than one would expect. It is possible to test for the influence of adapted preferences on instrument responses using measurement invariance testing. This study conducts such a test with the Wellbeing Related option-Freedom (WeRFree) and ICECAP-A instruments.

METHODS

A multi-group confirmatory factor analysis was conducted to iteratively test four increasingly stringent types of measurement invariance: (1) configural invariance, (2) metric invariance, (3) scalar invariance, and (4) residual invariance. Data from the Multi Instrument Comparison study were divided into subsamples that reflect groups of participants that differ by age, gender, education, or health condition. Measurement invariance was assessed with (changes in) the Comparative Fit Index (CFI), Root Mean Square Error of Approximation (RMSEA), and Root Mean Square Residual (SRMR) fit indices.

RESULTS

For the WeRFree instrument, full measurement invariance could be established in the gender and education subsamples. Scalar invariance, but not residual invariance, was established in the health condition and age group subsamples. For the ICECAP-A, full measurement invariance could be established in the gender, education, and age group subsamples. Scalar invariance could be established in the health group subsample.

CONCLUSIONS

This study tests the measurement invariance properties of the WeRFree and ICECAP-A instruments. The results indicate that these instruments were scalar invariant in all subsamples, which means that group means can be compared across different subpopulations. We suggest that measurement invariance of capability instruments should routinely be tested with a reference group that does not experience a disadvantage to study whether responses could be affected by adapted preferences.

Cross-cultural measurement invariance of the Quality of Life Enjoyment and Satisfaction Questionnaire-Short form across ten countries: the application of Bayesian approximate measurement invariance

Background

The Quality of Life Enjoyment and Satisfaction Questionnaire-Short Form (Q-LES-Q-SF) is the most frequently used generic quality of life (QOL) measure in many countries and cultures worldwide. However, no single study has been carried out to investigate whether this questionnaire performs similarly across diverse cultures/countries. Accordingly, this study aimed to assess the cross-cultural measurement invariance of the Q-LES-Q-SF across ten different countries.

Methods

The Q-LES-Q-SF was administrated to a sample of 2822 university students from ten countries: Bangladesh, Brazil, Croatia, India, Nepal, Poland, Serbia, Turkey, the United Arab Emirates, and Vietnam. The Bayesian approximate measurement invariance approach was used to assess the measurement invariance of the Q-LES-Q-SF.

Results

Approximate measurement invariance did not hold across the countries for the Q-LES-Q-SF, with only two out of 14 items being non-invariant; namely items related to doing household and leisure time activities.

Conclusions

Our findings did not support the cross-cultural measurement invariance of the Q-LES-Q-SF; thus, considerable caution is warranted when comparing QOL scores across different countries with this measure. Item rewording and adaptation along with calibrating non-invariant items may narrow these differences and help researchers to create an invariant questionnaire for reliable and valid QOL comparisons across different countries.

A Machine Learning Approach to Assess Differential Item Functioning in Psychometric Questionnaires Using the Elastic Net Regularized Ordinal Logistic Regression in Small Sample Size Groups

Assessing differential item functioning (DIF) using the ordinal logistic regression (OLR) model highly depends on the asymptotic sampling distribution of the maximum likelihood (ML) estimators. The ML estimation method, which is often used to estimate the parameters of the OLR model for DIF detection, may be substantially biased with small samples. This study is aimed at proposing a new application of the elastic net regularized OLR model, as a special type of machine learning method, for assessing DIF between two groups with small samples. Accordingly, a simulation study was conducted to compare the powers and type I error rates of the regularized and nonregularized OLR models in detecting DIF under various conditions including moderate and severe magnitudes of DIF (DIF = 0.4 and 0.8), sample size (N), sample size ratio (R), scale length (I), and weighting parameter (w). The simulation results revealed that for I = 5 and regardless of R, the elastic net regularized OLR model with w = 0.1, as compared with the nonregularized OLR model, increased the power of detecting moderate uniform DIF (DIF = 0.4) approximately 35% and 21% for N = 100 and 150, respectively. Moreover, for I = 10 and severe uniform DIF (DIF = 0.8), the average power of the elastic net regularized OLR model with 0.03 ≤ w ≤ 0.06, as compared with the nonregularized OLR model, increased approximately 29.3% and 11.2% for N = 100 and 150, respectively. In these cases, the type I error rates of the regularized and nonregularized OLR models were below or close to the nominal level of 0.05. In general, this simulation study showed that the elastic net regularized OLR model outperformed the nonregularized OLR model especially in extremely small sample size groups. Furthermore, the present research provided a guideline and some recommendations for researchers who conduct DIF studies with small sample sizes.

Assessing the measurement invariance of the 10-item Centre for Epidemiological Studies Depression Scale and Beck Anxiety Inventory questionnaires across people living with HIV/AIDS and healthy people

Background

Recently, extensive research has been reported the higher rate of depression and anxiety among people living with HIV/AIDS (PLWHAs) as compared to the general population. However, no single study has been carried out to investigate whether this disparity is a real difference or it happens due to lack of measurement invariance. This study aims to assess the measurement invariance of the Beck Anxiety Inventory (BAI) and 10-item Centre for Epidemiological Studies Depression Scale (CESD-10) questionnaires across PLWHAs and healthy individuals.

Methods

One hundred and fifty PLWHAs and 500 healthy individuals filled out the Persian version of the BAI and CESD-10 questionnaires. Multi-group multiple-indicators multiple-causes model (MG-MIMIC) was used to assess measurement invariance across PLWHAs and healthy people.

Results

Our findings revealed that PLWHAs and healthy individuals perceived the meaning of all the items in the BAI and CESD-10 questionnaires similarly. In addition, although depression scores were significantly higher in PLWHAs as opposed to the healthy individuals, no significant difference was observed in anxiety scores of these two groups.

Conclusions

The current study suggests that the BAI and CESD-10 are invariant measures across PLWHAs and healthy people which can be used for meaningful cross-group comparison. Therefore, in comparison to healthy individuals, higher depression score of PLWHAs is a real difference. It is highly recommended that health professionals develop therapeutic interventions and psychological supports to promote the mental health of PLWHAs which alleviate their depressive symptoms.

Negligible Effects of the Survey Modes for Patient-Reported Outcomes: A Report From the Childhood Cancer Survivor Study

PURPOSE

This study compared the measurement properties for multiple modes of survey administration, including postal mail, telephone interview, and Web-based completion of patient-reported outcomes (PROs) among survivors of childhood cancer.

METHODS

The population included 6,974 adult survivors of childhood cancer in the Childhood Cancer Survivor Study who completed the Brief Symptom Inventory-18 (BSI-18), which measured anxiety, depression, and somatization symptoms. Scale reliability, construct validity, and known-groups validity related to health status were tested for each mode of completion. The multiple indicators and multiple causes technique was used to identify differential item functioning (DIF) for the BSI-18 items that responded through a specific survey mode. The impact of the administration mode was tested by comparing differences in BSI-18 scores between the modes accounting for DIF effects.

RESULTS

Of the respondents, 58%, 27%, and 15% completed postal mail, Web-based, and telephone surveys, respectively. Survivors who were male; had lower education, lower household income, or poorer health status; or were treated with cranial radiotherapy were more likely to complete a telephone-based survey compared with either a postal mail or Web-based survey (all P < .05). Scale reliability and validity were equivalent across the 3 survey options. One, 2, and 5 items from the anxiety, depression, and somatization domains, respectively, were identified as having significant DIF among survivors who responded by telephone (P < .05). However, estimated BSI-18 domain scores, especially depression and anxiety, between modes did not differ after accounting for DIF effects.

CONCLUSION

Certain survivor characteristics were associated with choosing a specific mode for PRO survey completion. However, measurement properties among these modes were equivalent, and the impact of using a specific mode on scores was minimal.

Psychometric validation of the French self and proxy versions of the PedsQL™ 4.0 generic health-related quality of life questionnaire for 8-12 year-old children

BACKGROUND

The Pediatric Quality of Life Inventory Version 4.0 (PedsQL^TM4.0) is a generic health-related quality of life (HRQoL) questionnaire, widely used in pediatric clinical trials but not yet validated in France. We performed the psychometric validation of the self and proxy PedsQL^TM4.0 generic questionnaires for French children aged 8-12 years old.

METHODS

This bicentric cross-sectional study included 123 children and their parents with congenital heart disease (CHD) and 97 controls. The psychometric validation method was based on the consensus-based standards for the selection of health measurement instruments (COSMIN). The reliability was tested using the intraclass correlation coefficient (ICC). To evaluate the validity of this scale, content, face, criterion, and construct validity psychometric proprieties were tested. Acceptability was studied regarding questionnaires' completion and the existence of a floor or a ceiling effect.

RESULTS

Test-retest reliability intra-class correlation coefficients were mainly in good range (0.49-0.66). Face validity was very good among parents (0.85) and children (0.75). Content validity was good (0.70), despite misinterpretation of some items. In construct validity, each subscale had acceptable internal consistency reliability (Cronbach's α > 0.72 in self-reports, > 0.69 in proxy-reports). In the confirmatory factor analysis, the goodness-of-fit statistics rejected the original structure with 4 factors. The exploratory factor analysis revealed an alternative two-factor structure corresponding to physical and psychological dimensions. Convergent validity was supported by moderate (> 0.41) to high correlations (0.57) between PedsQL and Kidscreeen questionnaires for physical, emotion and school dimensions. The ability of the PedsQL to discriminate CHD severity was better with physical, social and total scores for both self-reports and proxy-reports.

CONCLUSIONS

The PedsQL^TM4.0 generic self and proxy HRQoL questionnaires found good psychometric properties, with regard to acceptability, responsiveness, validity, and reliability. This instrument appeared to be easy to use and comprehend within the target population of children aged 8 to 12 years old and their parents.

TRIAL REGISTRATION

This study was approved by the South-Mediterranean-IV Ethics Committee and registered on ClinicalTrials.gov (NCT01202916), https://clinicaltrials.gov/ct2/show/NCT01202916 .

A Comparative Study of the Bias Correction Methods for Differential Item Functioning Analysis in Logistic Regression with Rare Events Data

The logistic regression (LR) model for assessing differential item functioning (DIF) is highly dependent on the asymptotic sampling distributions. However, for rare events data, the maximum likelihood estimation method may be biased and the asymptotic distributions may not be reliable. In this study, the performance of the regular maximum likelihood (ML) estimation is compared with two bias correction methods including weighted logistic regression (WLR) and Firth's penalized maximum likelihood (PML) to assess DIF for imbalanced or rare events data. The power and type I error rate of the LR model for detecting DIF were investigated under different combinations of sample size, moderate and severe magnitudes of uniform DIF (DIF = 0.4 and 0.8), sample size ratio, number of items, and the imbalanced degree (τ). Indeed, as compared with WLR and for severe imbalanced degree (τ = 0.069), there were reductions of approximately 30% and 24% under DIF = 0.4 and 27% and 23% under DIF = 0.8 in the power of the PML and ML, respectively. The present study revealed that the WLR outperforms both the ML and PML estimation methods when logistic regression is used to evaluate DIF for imbalanced or rare events data.

Generische und indikationsspezifische Messeigenschaften des IRES-24-Patientenfragebogen

Zusammenfassung. Der Indikatoren des Reha-Status Patientenfragebogen (IRES-24) wird in der medizinischen Rehabilitation als Instrument zur Routinediagnostik der Dimensionen Funktionsfähigkeit im Alltag, Psychisches Befinden, Somatische Gesundheit und Schmerzen eingesetzt. Die generischen und indikationsspezifischen Messeigenschaften des IRES-24 Patientenfragebogen werden in einem Vergleich von Befragten aus der orthopädischen (N = 1 869; 37 % weiblich; MAlter = 50.3 Jahre) und der neurologischen Rehabilitation (N = 881; 49 % weiblich; MAlter = 64.6 Jahre) analysiert. Um Alters- und Geschlechtsverzerrungen zu vermeiden, wurden gematchte Stichproben gezogen (342 Befragte pro Gruppe; 55 % weiblich; MAlter = 51.6 bzw. 52.6 Jahre). Die Analyse erfolgte mittels des Differential Item Functioning auf Basis des ordinalen Rasch-Modells. Während Psychisches Befinden indikationsübergreifend testfair erfasst wird, indizieren einzelne Items der Skala Funktionsfähigkeit im Alltag und Schmerzen die jeweilige latente Merkmalsdimension unterschiedlich sensitiv. Bedeutsame Verletzungen der Homogenität der Skala Somatische Gesundheit, die durch die Erfassung unterschiedlicher Symptomkomplexe bedingt sind, müssen bei indikationsübergreifenden Anwendungen des IRES-24 berücksichtigt werden.

A comparison of children and adolescent's self-report and parental report of the PedsQL among those with and without autism spectrum disorder

PURPOSE

Children and adolescents with autism spectrum disorders (ASD) are understood to experience a reduced quality of life compared to typically developing (TD) peers. The evidence to support this has largely been derived from proxy reports, in turn which have been evaluated by Cronbach's alpha and interrater reliability, neither of which demonstrate unidimensionality of scales, or that raters use the instruments consistently. To redress this, we undertook an evaluation of the Pediatric Quality of Life Inventory™ (PedsQL), a widely used measure of children's quality of life. Three questions were explored: (1). do TD children or adolescents and their parents use the PedsQL differently; (2). do children or adolescents with ASD and their parents use the PedsQL differently, and (3). do children or adolescents with ASD and TD children or adolescents use the PedsQL differently? By using the scales differently, we mean whether respondents endorse items differently contingent by group.

METHODS

We recruited 229 children and adolescents with ASD who had an IQ greater than 70, and one of their parents, as well as 74 TD children or adolescents and one of their parents. Children and adolescents with ASD (aged 6-20 years) were recruited from special primary and secondary schools in the Amsterdam region. Children and adolescents were included based on an independent clinical diagnosis established prior to recruitment according to DSM-IV-TR criteria by psychiatrists and/or psychologists, qualified to make the diagnosis. Children or adolescents and parents completed their respective version of the PedsQL.

RESULTS

Data were analysed for unidimensionality and for differential item functioning (DIF) across respondent for TD children and adolescents and their parents, for children and adolescents with ASD and their parents, and then last, children and adolescents with ASD were compared to TD children and adolescents for DIF. Following recoding the data, the unidimensional model was found to fit all groups. We found that parents of and TD children and adolescents do not use the PedsQL differently ([Formula: see text] = 64.86, p = ns), consistent with the literature that children and adolescents with ASD and TD children and adolescents use the PedsQL similarly ([Formula: see text] = 92.22, p = ns), though their score levels may differ. However, children and adolescents with ASD and their parents respond to the PedsQL differently ([Formula: see text] = 190.22, p < 0.001) and contingently upon features of the child or adolescent.

CONCLUSIONS

We suggest this is due to children or adolescents with ASD being less forthcoming with their parents about their lives. This, however, will require additional research to confirm. Consequently, we conclude that parents of high-functioning children with ASD are unable to act as reliable proxies for their children with ASD.

Testing whether patients with diabetes and healthy people perceive the meaning of the items in the Persian version of the SF-36 questionnaire similarly: a differential item functioning analysis

PURPOSE

It has been rarely studied whether observed disparity in health-related quality-of-life (HRQoL) scores between patients with diabetes and healthy individuals is due to differential item functioning (DIF) or a true difference in the underlying construct. This study aimed to examine DIF in the SF-36 questionnaire and its effect on comparing HRQoL scores between patients with diabetes and healthy people.

METHODS

The sample consisted of 230 patients with type 2 diabetes and 642 healthy individuals who filled out the Persian version of the SF-36 questionnaire. To detect DIF across patients with diabetes and healthy individuals, multiple-group multiple-indicator multiple-causes model was used. In addition, item calibration strategy was used to determine whether the effect of item-level DIF was transferred to the scale level.

RESULTS

Nine out of thirty-six (25 %) items were detected as DIF, of which one item (11 %) was flagged as uniform and eight items (89 %) as non-uniform DIF. Most of the DIF items were detected in the mental health component which includes vitality, perceived mental health and social functioning subscales rather than in physical health component. Moreover, nonsignificant latent mean differences for general health perception and social functioning subscales became significant after DIF calibration.

CONCLUSION

The findings of the present study show that patients with diabetes and healthy individuals perceived some items in the SF-36 questionnaire differently. More importantly, in some subscales, the effect of item-level DIF was transferred to the scale level. Consequently, considerable caution should be taken in comparing HRQoL scores between patients with diabetes and healthy individuals.

A New Measurement Equivalence Technique Based on Latent Class Regression as Compared with Multiple Indicators Multiple Causes

Background:

Measurement equivalence is an essential prerequisite for making valid comparisons in mental health questionnaires across groups. In most methods used for assessing measurement equivalence, which is known as Differential Item Functioning (DIF), latent variables are assumed to be continuous.

Objective:

To compare a new method called Latent Class Regression (LCR) designed for discrete latent variable with the multiple indicators multiple cause (MIMIC) as a continuous latent variable technique to assess the measurement equivalence of the 12-item General Health Questionnaire (GHQ-12), which is a cross deferent subgroup of Iranian nurses.

Methods:

A cross-sectional survey was conducted in 2014 among 771 nurses working in the hospitals of Fars and Bushehr provinces of southern Iran. To identify the Minor Psychiatric Disorders (MPD), the nurses completed self-report GHQ-12 questionnaires and sociodemographic questions. Two uniform-DIF detection methods, LCR and MIMIC, were applied for comparability when the GHQ-12 score was assumed to be discrete and continuous, respectively.

Results:

The result of fitting LCR with 2 classes indicated that 27.4% of the nurses had MPD. Gender was identified as an influential factor of the level of MPD.LCR and MIMIC agree with detection of DIF and DIF-free items by gender, age, education and marital status in 83.3, 100.0, 91.7 and 83.3% cases, respectively.

Conclusions:

The results indicated that the GHQ-12 is to a great degree, an invariant measure for the assessment of MPD among nurses. High convergence between the two methods suggests using the LCR approach in cases of discrete latent variable, e.g. GHQ-12 and adequate sample size.

A Simulation Study to Assess the Effect of the Number of Response Categories on the Power of Ordinal Logistic Regression for Differential Item Functioning Analysis in Rating Scales

Objective. The present study uses simulated data to find what the optimal number of response categories is to achieve adequate power in ordinal logistic regression (OLR) model for differential item functioning (DIF) analysis in psychometric research. Methods. A hypothetical ten-item quality of life scale with three, four, and five response categories was simulated. The power and type I error rates of OLR model for detecting uniform DIF were investigated under different combinations of ability distribution (θ), sample size, sample size ratio, and the magnitude of uniform DIF across reference and focal groups. Results. When θ was distributed identically in the reference and focal groups, increasing the number of response categories from 3 to 5 resulted in an increase of approximately 8% in power of OLR model for detecting uniform DIF. The power of OLR was less than 0.36 when ability distribution in the reference and focal groups was highly skewed to the left and right, respectively. Conclusions. The clearest conclusion from this research is that the minimum number of response categories for DIF analysis using OLR is five. However, the impact of the number of response categories in detecting DIF was lower than might be expected.

Cross-cultural Measurement Equivalence of the KINDL Questionnaire for Quality of Life Assessment in Children and Adolescents

This cross-cultural study aimed to assess whether Iranian and Serbian children, and also their parents, perceived the meaning of the items in the KINDL quality of life questionnaire consistently. The sample included 1086 Iranian and 756 Serbian children and adolescents, alongside 1061 and 618 of their parents, respectively. The ordinal logistic regression was used to assess differential item functioning (DIF) of the self and proxy-reports of the two versions of the KINDL, including Kid-KINDL and Kiddo-KINDL, across Iranian and Serbian samples. Statistically significant DIF was flagged for 14 out of 24 (58%) and 20 out of 24 (83%) items in the self-report of the Kid-KINDL and Kiddo-KINDL, respectively. Moreover, 20 out of 24 (83%) in the proxy reports of the both Kid-KINDL and Kiddo-KINDL, showed DIF across two samples. Accordingly, considerable caution is warranted when using the KINDL for cross-cultural comparisons.

Patient-Reported Health in Young People With Congenital Heart Disease Transitioning to Adulthood

PURPOSE

Because life expectancy of patients with congenital heart disease (CHD) has increased substantially, assessment of patient-reported health is seen as an important component in the follow-up. Therefore, we (1) examined patient-reported health status of young people with CHD from a longitudinal perspective; (2) compared patient-reported health of patients with that of controls from the general population; and (3) investigated longitudinal interrelationships among various domains of patient-reported health.

METHODS

We included 429 patients with CHD (aged 14-18 years) in a longitudinal study with four measurement points. Patient-reported health status was measured using a linear analog scale for self-rated health and the Pediatric Quality of Life Inventory (PedsQL).

RESULTS

Self-rated health was good, with mean scores that slightly decreased from 81.78 to 78.90 from Time 1 to Time 4. PedsQL scores were also good, with the highest scores obtained for physical functioning. Patients with mild heart defects consistently reported higher scores on self-rated health and PedsQL than the general population. The scores of patients with complex heart defects were generally lower than those of the general population. Cross-lagged path analyses demonstrated that symptoms, cognitive functioning, and communication problems constituted the most consistent predictors of perceived health domains over time.

CONCLUSIONS

Patient-reported health was considerably good. Domains of patient-reported health that deserve specific attention are symptoms, cognitive functioning, and communication problems. Intervening in these three domains may yield indirect benefits on other health status domains and may improve the overall perceived health status of young people with CHD.

Adolescent body weight and health-related quality of life rated by adolescents and parents: the issue of measurement bias

Background

Evidence is sparse about whether body weight categories in adolescents are associated with differences in pediatric HRQoL rated by adolescents and parents. Additionally, it is unknown whether HRQoL rated by individuals with different body mass index (BMI) weight categories is psychometrically comparable. This study aimed to assess whether difference in pediatric HRQoL rated by adolescents and their parents was explained by BMI weight status, and to test measurement properties of HRQoL items related to weight categories using differential item functioning (DIF) methodology. DIF refers to the situation when the individuals across subgroups rate an item differently (e.g., item score three by one subgroup and four by another) given the same underlying construct.

Methods

A cross-sectional study utilizing a sample of parents (n = 323) and their adolescents aged 15–18 years old (n = 323) who enrolled in Florida’s Medicaid. Adolescent self-reports and parent proxy-reports of the Pediatric Quality of Life Inventory was adopted to measure pediatric HRQoL. We classified body weight categories as normal weight, overweight, and obesity. A Multiple Indicator Multiple Cause (MIMIC) method was used to assess DIF associated with BMI weight status, especially testing the disparity in the parameters of different weight categories (reference: lower weight category) associated with a response to a HRQoL item conditioning on the same underlying HRQoL. DIF analyses were conducted by adolescent self-reports and parent proxy-reports.

Results

Parents reported lower pediatric HRQoL across all domains than adolescents did. Excess body weight (combined overweight and obese) was significantly associated with a greater discrepancy in the rating of emotional and total functioning between adolescents and parents (p < 0.05). DIF associated with BMI weight categories was identified by two items in adolescent self-reports and five items in parent proxy-reports.

Conclusions

Adolescents’ BMI weight categories significantly contribute to a difference in the rating of pediatric HRQoL by adolescents and parents.

Testing measurement equivalence of the SF-36 questionnaire across patients on hemodialysis and healthy people

BACKGROUND

Differential item functioning (DIF) occurs when members from different groups respond differently to particular items in a health-related quality of life (HRQoL) questionnaire after controlling for underlying HRQoL construct. This study aimed to assess DIF in the SF-36 questionnaire and its effect on comparing HRQoL scores across patients on HD and healthy people.

METHODS

One hundred fifty patients on maintenance hemodialysis (HD) and 642 healthy individuals filled out the Persian version of the SF-36 questionnaire. Multiple-group multiple-indicator multiple-causes (MG-MIMIC) model was used to assess DIF across patients on HD and healthy population.

RESULTS

Sixteen out of 36 (44.4 %) items were flagged with DIF. Six out of 16 items (37.5 %) were flagged with uniform DIF, nine items (56.2 %) with non-uniform DIF, and one item (6.2 %) with both uniform DIF and non-uniform DIF. DIF items were associated with all subscales with the exception of the limitation due to physical problems and bodily pain subscales. The significant lower HRQoL scores of patients on HD in comparison with healthy people in the physical functioning and vitality subscales did not change after removing the items with uniform DIF.

CONCLUSIONS

Our findings revealed that patients on HD and healthy people perceived the meaning of the items in SF-36 questionnaire differently. Although the impact of DIF is minimal, the cross-group comparison across patients on HD and healthy people should be performed with caution.

Developing item banks for measuring pediatric generic health-related quality of life: an application of the International Classification of Functioning, Disability and Health for Children and Youth and item response theory

The purpose of this study was to develop item banks by linking items from three pediatric health-related quality of life (HRQoL) instruments using a mixed methodology. Secondary data were collected from 469 parents of children aged 8-16 years. The International Classification of Functioning, Disability and Health-Children and Youth (ICF-CY) served as a framework to compare the concepts of items from three HRQoL instruments. The structural validity of the individual domains was examined using confirmatory factor analyses. Samejima's Graded Response Model was used to calibrate items from different instruments. The known-groups validity of each domain was examined using the status of children with special health care needs (CSHCN). Concepts represented by the items in the three instruments were linked to 24 different second-level categories of the ICF-CY. Eight item banks representing eight unidimensional domains were created based on the linkage of the concepts measured by the items of the three instruments to the ICF-CY. The HRQoL results of CSHCN in seven out of eight domains (except personality) were significantly lower compared with children without special health care needs (p<0.05). This study demonstrates a useful approach to compare the item concepts from the three instruments and to generate item banks for a pediatric population.

Measurement equivalence of the KINDL questionnaire across child self-reports and parent proxy-reports: a comparison between item response theory and ordinal logistic regression

Measurement equivalence is a necessary assumption for meaningful comparison of pediatric quality of life rated by children and parents. In this study, differential item functioning (DIF) analysis is used to examine whether children and their parents respond consistently to the items in the KINDer Lebensqualitätsfragebogen (KINDL; in German, Children Quality of Life Questionnaire). Two DIF detection methods, graded response model (GRM) and ordinal logistic regression (OLR), were applied for comparability. The KINDL was completed by 1,086 school children and 1,061 of their parents. While the GRM revealed that 12 out of the 24 items were flagged with DIF, the OLR identified 14 out of the 24 items with DIF. Seven items with DIF and five items without DIF were common across the two methods, yielding a total agreement rate of 50 %. This study revealed that parent proxy-reports cannot be used as a substitute for a child's ratings in the KINDL.