Negligible impact of differential item functioning between Black and White dialysis patients on the Kidney Disease Quality of Life 36-item short form survey (KDQOLTM-36)

Purpose

Black dialysis patients report better health-related quality of life (HRQOL) than White patients, which may be explained if Black and White patients respond systematically differently to HRQOL survey items.

Methods

We examined differential item functioning (DIF) of the Kidney Disease Quality of Life 36-item (KDQOL^TM-36) Burden of Kidney Disease, Symptoms and Problems with Kidney Disease, and Effects of Kidney Disease scales between Black (n?=?18,404) and White (n?=?21,439) dialysis patients. We fit multiple group confirmatory factor analysis models with increasing invariance: a Configural model (invariant factor structure), a Metric model (invariant factor loadings), and a Scalar model (invariant intercepts). Criteria for invariance included non-significant χ² tests, > 0.002 difference in the models’ CFI, and >?0.015 difference in RMSEA and SRMR. Next, starting with a fully invariant model, we freed loadings and intercepts item-by-item to determine if DIF impacted estimated KDQOL^TM-36 scale means.

Results

ΔCFI was 0.006 between the metric and scalar models but was reduced to 0.001 when we freed intercepts for the burdens and symptoms and problems of kidney disease scales. In comparison to standardized means of 0 in the White group, those for the Black group on the Burdens, Symptoms and Problems, and Effects of Kidney Disease scales were 0.218, 0.061, and 0.161, respectively. When loadings and thresholds were released sequentially, differences in means between models ranged between 0.001 and 0.048.

Conclusion

Despite some DIF, impacts on KDQOL^TM-36 responses appear to be minimal. We conclude that the KDQOL^TM-36 is appropriate to make substantive comparisons of HRQOL between Black and White dialysis patients.

     

Use of factor analysis models to evaluate measurement invariance property of the Asthma Control Questionnaire (ACQ)

Purposes

To demonstrate the assessment of measurement invariance property in a health status instrument and to increase the awareness of its importance, we evaluate the measurement invariance of the Asthma Control Questionnaire (ACQ) across age and gender subgroups.

Methods

Data are obtained from children 7–12 years of age at entry into a randomized trial, which evaluates the effect of a telephone coaching program on improving asthma outcome. Multi-group confirmatory factor analysis is used to assess the comparability of factor loadings and intercepts across age and gender subgroups. Since age is a continuous variable, two different categorizations (7–10 vs 11–12 and 7–9 vs 10–12) are analyzed.

Results

The factor loadings and intercepts of all six items in ACQ are comparable across gender subgroups. Although the factor loadings are comparable across age 7–10 and 11–12 subgroups, one intercept is statistically but not practically different. For age 7–9 versus 10–12 subgroup comparison, the factor loadings are not comparable.

Conclusion

In children, the ACQ can be used to compare asthma control construct between boys and girls and between age 7–10 and 11–12 subgroups. Measurement invariance is an important property that should be examined when the latent construct(s) are compared across different subgroups.     

Testing for intersectional measurement invariance with the alignment method: Evaluation of the 8-item patient health questionnaire

Objective

To demonstrate the use of the alignment method to evaluate whether surveys function similarly (i.e., have evidence of measurement invariance) across culturally diverse intersectional groups. Intersectionality theory recognizes the interconnected nature of social categories such as race, gender, ethnicity, and socioeconomic status.

Data Sources

A total of 30,215 American adult's responses to the eight-item Patient Health Questionnaire depression assessment scale (PHQ-8) from the 2019 National Health Interview Survey (NHIS).

Study Design

Using the alignment method, we examined the measurement invariance (equivalence) of the PHQ-8 depression assessment scale across 16 intersectional subgroups defined at the intersection of age (under 52, 52 and older), gender (male, female), race (Black, non-Black), and education (no bachelor's degree, bachelor's degree).

Principal Findings

Overall, 24% of the factor loadings and 5% of the item intercepts showed evidence of differential functioning across one or more of the intersectional groups. These levels fall beneath the benchmark of 25% suggested for determining measurement invariance with the alignment method.

Conclusions

The results of the alignment study suggest that the PHQ-8 functions similarly across the intersectional groups examined, despite some evidence of different factor loadings and item intercepts in some groups (i.e., noninvariance). By examining measurement invariance through an intersectional lens, researchers can investigate how a person's multiple identities and social positions possibly contribute to their response behavior on an assessment scale.     

Evaluating measurement invariance across assessment modes of phone interview and computer self-administered survey for the PROMIS measures in a population-based cohort of localized prostate cancer survivors

Purpose

To evaluate measurement invariance (phone interview vs computer self-administered survey) of 15 PROMIS measures responded by a population-based cohort of localized prostate cancer survivors.

Methods

Participants were part of the North Carolina Prostate Cancer Comparative Effectiveness and Survivorship Study. Out of the 952 men who took the phone interview at 24 months post-treatment, 401 of them also completed the same survey online using a home computer. Unidimensionality of the PROMIS measures was examined using single-factor confirmatory factor analysis (CFA) models. Measurement invariance testing was conducted using longitudinal CFA via a model comparison approach. For strongly or partially strongly invariant measures, changes in the latent factors and factor autocorrelations were also estimated and tested.

Results

Six measures (sleep disturbance, sleep-related impairment, diarrhea, illness impact—negative, illness impact—positive, and global satisfaction with sex life) had locally dependent items, and therefore model modifications had to be made on these domains prior to measurement invariance testing. Overall, seven measures achieved strong invariance (all items had equal loadings and thresholds), and four measures achieved partial strong invariance (each measure had one item with unequal loadings and thresholds). Three measures (pain interference, interest in sexual activity, and global satisfaction with sex life) failed to establish configural invariance due to between-mode differences in factor patterns.

Conclusions

This study supports the use of phone-based live interviewers in lieu of PC-based assessment (when needed) for many of the PROMIS measures.

     

QLU-C10D: a health state classification system for a multi-attribute utility measure based on the EORTC QLQ-C30

Purpose

To derive a health state classification system (HSCS) from the cancer-specific quality of life questionnaire, the EORTC QLQ-C30, as the basis for a multi-attribute utility instrument.

Methods

The conceptual model for the HSCS was based on the established domain structure of the QLQ-C30. Several criteria were considered to select a subset of dimensions and items for the HSCS. Expert opinion and patient input informed a priori selection of key dimensions. Psychometric criteria were assessed via secondary analysis of a pooled dataset comprising HRQOL and clinical data from 2616 patients from eight countries and a range of primary cancer sites, disease stages, and treatments. We used confirmatory factor analysis (CFA) to assess the conceptual model’s robustness and generalisability. We assessed item floor effects (>75 % observations at lowest score), disordered item response thresholds, coverage of the latent variable and differential item function using Rasch analysis. We calculated effect sizes for known group comparisons based on disease stage and responsiveness to change. Seventy-nine cancer patients assessed the relative importance of items within dimensions.

Results

CFA supported the conceptual model and its generalisability across primary cancer sites. After considering all criteria, 12 items were selected representing 10 dimensions: physical functioning (mobility), role functioning, social functioning, emotional functioning, pain, fatigue, sleep, appetite, nausea, bowel problems.

Conclusions

The HSCS created from QLQ-C30 items is known as the EORTC Quality of Life Utility Measure-Core 10 dimensions (QLU-C10D). The next phase of the QLU-C10D’s development involves valuation studies, currently planned or being conducted across the globe.

     

Identifying health-related quality of life cut-off scores that indicate the need for supportive care in young adults with cancer

Purpose

Using patient-reported outcomes in routine cancer care may improve health outcomes. However, a lack of information about which scores are problematic in specific populations can impede use. To facilitate interpretation of the European Organisation for Research and Treatment of Cancer Core Questionnaire (EORTC QLQ-C30), we identified cut-off scores that indicate need for support by comparing each scale to relevant items from the Supportive Care Needs Survey (SCNS-LF59) in a young adult (YA) population.

Methods

We conducted a cross-sectional survey amongst YAs with cancer ages 25–39 at diagnosis. Participants completed the EORTC QLQ-C30 and SCNS-LF59. Patient, clinician and research experts matched supportive care needs from the SCNS-LF59 to quality of life domains of the EORTC QLQ-C30. We evaluated the EORTC QLQ-C30 domain score’s ability to detect patients with need using receiver operator characteristic (ROC) analysis, calculating the area under the ROC curve and sensitivity and specificity for selected cut-offs. Cut-offs were chosen by maximising Youden’s J statistic and ensuring sensitivity passed 0.70. Sensitivity analyses were conducted to examine the variability of the cut-off scores by treatment status.

Results

Three hundred and forty-seven YAs took part in the survey. Six experts matched SCNS-LF59 items to ten EORTC QLQ-C30 domains. The AUC ranged from 0.78 to 0.87. Cut-offs selected ranged from 8 (Nausea and Vomiting and Pain) to 97 (Physical Functioning). All had adequate sensitivity (above 0.70) except the Financial Difficulties scale (0.64). Specificity ranged from 0.61 to 0.88. Four of the cut-off scores differed by treatment status.

Conclusion

Cut-offs with adequate sensitivity were calculated for nine EORTC QLQ-C30 scales for use with YAs with cancer. Cut-offs are key to interpretability and use of the EORTC QLQ-C30 in routine care to identify patients with supportive care need.

     

Minimal clinically important differences in the EORTC QLQ-C30 and brief pain inventory in patients undergoing re-irradiation for painful bone metastases

Purpose

The EORTC QLQ-C30 and the Brief Pain Inventory (BPI) are validated tools for measuring quality of life (QOL) and the impact of pain in patients with advanced cancer. Interpretation of these instrument scores can be challenging and it is difficult to know what numerical changes translate to clinically significant impact in patients’ lives. To address this issue, our study sought to establish the minimal clinically important differences (MCID) for these two instruments in a prospective cohort of patients with advanced cancer and painful bone metastases.

Methods

Both anchor-based and distribution-based methods were used to estimate the MCID scores from patients enrolled in a randomized phase III trial evaluating two different re-irradiation treatment schedules. For the anchor-based method, the global QOL item from the QLQ-C30 was chosen as the anchor. Spearman correlation coefficients were calculated for all items and only those items with moderate or better correlation (|r| ≥ 0.30) with the anchor were used for subsequent analysis. A 10-point difference in the global QOL score was used to classify improvement and deterioration, and the MCID scores were calculated for each of these categories. These results were compared with scores obtained by the distribution-method, which estimates the MCID purely from the statistical characteristics of the sample population.

Results

A total of 375 patients were included in this study with documented pain responses and completed QOL questionnaires at 2 months. 9/14 items in the QLQ-C30 and 6/10 items in the BPI were found to have moderate or better correlation with the anchor. For deterioration, statistically significant MCID scores were found in all items of the QLQ-C30 and BPI. For improvement, statistically significant MCID scores were found in 7/9 items of the QLQ-C30 and 2/6 items of the BPI. The MCID scores for deterioration were uniformly higher than the MCIDs for improvement. Using the distribution-based method, there was good agreement between the 0.5 standard deviation (SD) values and anchor-based scores for deterioration. For improvement, there was less agreement and the anchor-based scores were lower than the 0.5 SD values obtained from the distribution-based method.

Conclusion

We present MCID scores for the QLQ-C30 and BPI instruments obtained from a large cohort of patients with advanced cancer undergoing re-irradiation for painful bone metastases. The results from this study were compared to other similar studies which showed larger MCID scores for improvement compared to deterioration. We hypothesize that disease trajectory and patient expectations are important factors in understanding the contrasting results. The results of this study can guide clinicians and researchers in the interpretation of these instruments.

     

Testing the measurement invariance of the University of Washington Self-Efficacy Scale short form across four diagnostic subgroups

Purpose

The University of Washington Self-Efficacy Scale (UW-SES) was originally developed for people with multiple sclerosis (MS) and spinal cord injury (SCI). This study evaluates the measurement invariance of the 6-item short form of the UW-SES across four disability subgroups. Evidence of measurement invariance would extend the UW-SES for use in two additional diagnostic groups: muscular dystrophy (MD) and post-polio syndrome (PPS).

Methods

Multi-group confirmatory factor analysis was used to evaluate successive levels of measurement invariance of the 6-item short form, the UW-SES: (a) configural invariance, i.e., equivalent item-factor structures between groups; (b) metric invariance, i.e., equivalent unstandardized factor loadings between groups; and (c) scalar invariance, i.e., equivalent item intercepts between groups. Responses from the four groups with different diagnostic disorders were compared: MD (n = 172), MS (n = 868), PPS (n = 225), and SCI (n = 242).

Results

The results of this study support that the most rigorous form of invariance (i.e., scalar) holds for the 6-item short form of the UW-SES across the four diagnostic subgroups.

Conclusions

The current study suggests that the 6-item short form of the UW-SES has the same meaning across the four diagnostic subgroups. Thus, the 6-item short form is validated for people with MD, MS, PPS, and SCI.

     

The Quality of Life Questionnaire Core 30 (QLQ-C30) and Functional Assessment of Cancer-General (FACT-G) differ in responsiveness,relative efficiency,and therefore required sample size

ObjectivesQuality of Life Questionnaire Core 30 (QLQ-C30) and Functional Assessment of Cancer Therapy–General (FACT-G) are widely used cancer-specific health-related quality of life (HRQOL) questionnaires. We aimed to compare their responsiveness with clinically important effects and statistical efficiency to detect such effects.Study Design and SettingSecondary analysis of QLQ-C30 and FACT-G data from a randomized controlled trial of Medical Qigong (n = 162 heterogeneous cancer patients). Difference in responsiveness (DR) and relative efficiency (RE) were calculated for five domains.ResultsFACT-G total score was more efficient than QLQ-C30 global scale for detecting change within the intervention arm [RE = 0.31 (0.083, 0.69)] and comparing change between trial arms [RE = 0.17 (0.009, 0.58)]. In the social domain, the QLQ-C30 scale was more responsive [DR = 0.28 (0.024, 0.54)] and more efficient within arm only [RE = 5.25 (1.21, 232.26)]. In the physical, functional/role, and emotional domains, neither questionnaire was more responsive or efficient.ConclusionFACT-G would require about one-third the sample of QLQ-C30 to detect a given change in overall HRQOL, whereas in the social domain, it would require five times the sample size. FACT-G won advantage in overall HRQOL by reduced “noise” (smaller standard deviation achieved by summing across 27 items), whereas QLQ-C30 won advantage in the social domain via a larger “signal” (achieved through well-targeted item content).     

Differential item functioning (DIF) in the EORTC QLQ-C30: a comparison of baseline, on-treatment and off-treatment data

Introduction Differential item functioning (DIF) analyses can be used to explore translation, cultural, gender or other differences in the performance of quality of life (QoL) instruments. These analyses are commonly performed using “baseline” or pretreatment data. We previously reported DIF analyses to examine the pattern of item responses for translations of the European Organisation for Research and Treatment of Cancer (EORTC) QLQ-C30 QoL instrument, using only data collected prior to cancer treatment. We now compare the consistency of these results with similar analyses of on-treatment and off-treatment assessments and explore whether item relationships differ from those at baseline. Methods Logistic regression DIF analyses were used to examine the translation of each item in each multi-item scale at the three time points, after controlling for the overall scale score and other covariates. The consistency of results at the three time points was explored. Results For most EORTC QLQ-C30 subscales, the DIF results were very consistent across the three time points. Results for the Nausea and Vomiting scale varied the most across assessments. Discussion The results indicated that DIF analyses were stable across each time point and that the same DIF effects were usually found regardless of the treatment status of the respondent.     

Dimensional structure and measurement invariance of the youth self-report across gender and age

PurposeThe aim of the present work was to examine the correlated eight-syndrome model of the Youth Self-Report (YSR) proposed by Ivanova et al [1], using a confirmatory factor analysis for ordinal data. Likewise, we explored the measurement invariance of the YSR across gender and age using multigroup comparisons, and checked whether there were differences in the latent means.MethodsThe sample was made up of 4,868 nonclinical adolescents (47.6% males), with a mean age of 14.6 years (SD = 1.6).ResultsThe correlated eight-syndrome model proposed by Ivanova et al [1] showed a reasonable fit to the data, both for the total sample and by participants' gender and age. Moreover, the factor-equivalence analysis showed that the hypothesized dimensional model was invariant across gender and age. Statistically significant differences were found when comparing latent means between the groups.ConclusionsThese results coincide with those found in the literature and are in support of the replicability, generalizability, and consistency of the eight-syndrome model of the YSR, as well as its measurement invariance across gender and age. Future studies should explore the measurement invariance of this model through multigroup comparisons across cultures.     

The perceived constraints subscale of the Sense of Mastery Scale: dimensionality and measurement invariance

Purpose

A number of studies have reported differences in sense of mastery and perceived control across different subgroups. Yet, few have examined measurement invariance, an important prerequisite for valid comparisons. This study examines the factorial structure and measurement invariance of the perceived constraints (PC) facet of Pearlin and Schooler’s (1981) Sense of Mastery Scale (SM) which is a commonly used short form of the widely used SM scale.

Methods

Confirmatory factor analyses using AMOS and Mplus were conducted to explore dimensionality and test for measurement invariance in factor structure, factor loadings, intercepts, and residual variances across gender, age, education, income, and employment status in a large (N = 19,858), nationally representative sample of Norwegian males and females aged 16–100.

Results

The data supported a modified unidimensional model specifying correlations between the error terms of items 4 and 5, or possibly two highly correlated dimensions (r = 0.90). Metric invariance of the scale was shown for age, education, and employment, whereas invariance at the strong and strict levels was shown for gender and income. Partial invariance at the strong level was shown for age.

Conclusions

This Norwegian study supported a modified unidimensional structure for the abbreviated SM scale. Invariance testing indicated that comparisons across genders and income levels are unproblematic, whilst comparing mean scores across education and employment status is not justified. Latent, but not sum score means are comparable across age. Future studies using all 7 items of SM scale should provide more information on dimensionality and measurement invariance.

     

Psychometric evaluation of an item bank for computerized adaptive testing of the EORTC QLQ-C30 cognitive functioning dimension in cancer patients

Background

The European Organisation of Research and Treatment of Cancer (EORTC) Quality of Life Group is developing computerized adaptive testing (CAT) versions of all EORTC Quality of Life Questionnaire (QLQ-C30) scales with the aim to enhance measurement precision. Here we present the results on the field-testing and psychometric evaluation of the item bank for cognitive functioning (CF).

Methods

In previous phases (I–III), 44 candidate items were developed measuring CF in cancer patients. In phase IV, these items were psychometrically evaluated in a large sample of international cancer patients. This evaluation included an assessment of dimensionality, fit to the item response theory (IRT) model, differential item functioning (DIF), and measurement properties.

Results

A total of 1030 cancer patients completed the 44 candidate items on CF. Of these, 34 items could be included in a unidimensional IRT model, showing an acceptable fit. Although several items showed DIF, these had a negligible impact on CF estimation. Measurement precision of the item bank was much higher than the two original QLQ-C30 CF items alone, across the whole continuum. Moreover, CAT measurement may on average reduce study sample sizes with about 35–40% compared to the original QLQ-C30 CF scale, without loss of power.

Conclusion

A CF item bank for CAT measurement consisting of 34 items was established, applicable to various cancer patients across countries. This CAT measurement system will facilitate precise and efficient assessment of HRQOL of cancer patients, without loss of comparability of results.

     

The EORTC computer-adaptive tests measuring physical functioning and fatigue exhibited high levels of measurement precision and efficiency

ObjectivesThe European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Group is developing a computer-adaptive test (CAT) version of the EORTC Quality of Life Questionnaire (QLQ-C30). We evaluated the measurement properties of the CAT versions of physical functioning (PF) and fatigue (FA) and compared these with the corresponding QLQ-C30 scales.Study Design and SettingBased on international samples of more than 1,000 cancer patients, we simulated CAT administration of varying numbers of items and compared the resulting scores with those based on all items in the respective item pools. Furthermore, the relative validity (RV) of CATs was compared with that of the QLQ-C30 scales using known groups validity.ResultsFor both dimensions, CATs of all lengths resulted in unbiased score estimates. CATs consisting of five or more items had reliability>0.90, correlated ≥0.97 with the full scale, and had root mean square error <0.25. The average RVs for these CATs ranged 1.02–1.33, indicating possible savings in sample size requirements of 3–42% using CAT.ConclusionThe CAT versions of PF and FA exhibited high levels of measurement precision and efficiency. The potential savings in sample size requirements using CATs compared with those using the original QLQ-C30 scales were typically 20% or more.     

Most domains of the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire C30 are reliable

ObjectivesThe study's aim was to assess the internal reliability for the nine domains of the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30) to evaluate homogeneity across clinical studies and whether sample characteristics predict coefficient heterogeneity.Study Design and SettingA systematic literature review was undertaken. Internal reliability was assessed against Cronbach α coefficient >0.70. Reliability generalization was undertaken using fixed- and random-effects models. A weighted least squares regression model was applied to determine whether baseline sample characteristics (language, percentage of women, sample size, sample means and standard deviations, and cancer type) predicted variation in α coefficients.ResultsA total of 33 studies were identified. Eight domains demonstrated good internal reliability (unweighted/weighted by sample variance). One domain, Cognitive Functioning, consistently performed poorly. In terms of moderating variables, none of the sample characteristic variables explained sample variance for the Physical or Role Functioning domains. For the other domains, language, percentage of women, and sample means and variances accounted for some of the heterogeneity observed.ConclusionMost domains on the EORTC QLQ-C30 are reliable and may therefore be used to help inform decision-making processes, such as those involving individual patients.     

Measurement invariance of the WHOQOL-AGE questionnaire across three European countries

Purpose

Developing valid and reliable instruments that can be used across countries is necessary. The present study aimed to test the comparability of quality of life scores across three European countries (Finland, Poland, and Spain).

Method

Data from 9987 participants interviewed between 2011 and 2012 were employed, using nationally representative samples from the Collaborative Research on Ageing in Europe project. The WHOQOL-AGE questionnaire is a 13-item test and was employed to assess the quality of life in the three considered countries. First of all, two models (a bifactor model and a two-correlated factor model) were proposed and tested in each country by means of confirmatory factor models. Second, measurement invariance across the three countries was tested using multi-group confirmatory factor analysis for that model which showed the best fit. Finally, differences in latent mean scores across countries were analyzed.

Results

The results indicated that the bifactor model showed more satisfactory goodness-of-fit indices than the two-correlated factor model and that the WHOQOL-AGE questionnaire is a partially scalar invariant instrument (only two items do not meet scalar invariance). Quality of life scores were higher in Finland (considered as the reference category: mean?=?0, SD?=?1) than in Spain (mean?=???0.547, SD?=?1.22) and Poland (mean?=???0.927, SD?=?1.26).

Conclusions

Respondents from Finland, Poland, and Spain attribute the same meaning to the latent construct studied, and differences across countries can be due to actual differences in quality of life. According to the results, the comparability across the different considered samples is supported and the WHOQOL-AGE showed an adequate validity in terms of cross-country validation. Caution should be exercised with the two items which did not meet scalar invariance, as potential indicator of differential item functioning.

     

Health-Related Quality of Life and Health Utilities in Metastatic Castrate-Resistant Prostate Cancer: A Survey Capturing Experiences from a Diverse Sample of UK Patients

BackgroundThe collection of preference-based health outcomes data (or utility values) is required to support cost-effectiveness analyses.ObjectiveThis study aimed to collect health-related quality of life (HRQOL) data in men with metastatic castration-resistant prostate cancer (CRPC) stratified by disease states.MethodsMen with metastatic CRPC were recruited via UK patient associations, patient panels, and specialist recruiters and classified into four subgroups reflecting disease state: asymptomatic/mildly symptomatic before chemotherapy, symptomatic before chemotherapy, receiving chemotherapy, and postchemotherapy. HRQOL data (including five-level EuroQol five-dimensional questionnaire [EQ-5D-5L], European Organization for Research and Treatment of Cancer Core Quality of Life Questionnaire [EORTC QLQ-C30], and 25-item prostate cancer–specific questionnaire module designed to supplement the EORTC QLQ-C30) along with background and medical history data were collected via an online survey. The EQ-5D-5L and the EORTC-8D (EORTC-8D is an 8 dimensional utility index scored from QLQ-C30 data) were both used to estimate utilities.ResultsData were collected from a total sample of 163 men with metastatic CRPC. Utility values elicited by the EQ-5D-5L ranged from 0.830 for the asymptomatic/mildly symptomatic before chemotherapy disease state (95% confidence interval [CI] 0.795–0.865) to 0.625 for the symptomatic before chemotherapy disease state (95% CI 0.577–0.673). EORTC-8D utilities ranged from 0.856 (95% CI 0.831–0.882) to 0.697 (95% CI 0.664–0.731) for the same disease/treatment states.ConclusionsThis online survey was designed to capture real-world HRQOL data describing men with CRPC. The study estimated utilities using two alternative methods, and the results show good agreement, suggesting that they are robust. This methodology offers a potentially higher quality alternative to vignette-based methods that are commonly used in oncology submissions.     

The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30): Validation Study of the Thai Version

The objective of this study was to assess the psychometric properties of the Thai version of the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30) version 3.0. The questionnaire was completed by 310 cancer patients during their follow-up at 2 teaching hospital oncology clinics. About 70% of participants had advanced stage of cancer and 72% had been receiving chemotherapy. Cronbach’s α coefficients of the six scales were above 0.7, except for cognitive and social function scales. All test–retest reliability coefficients were high. Multitrait scaling analysis showed that all item-scale correlation coefficients met the standards of convergent and discriminant validity. Most scales and items could discriminate between subgroups of patients with different clinical status assessed with the Eastern Cooperative Oncology Group (ECOG) scale. The results suggested that the EORTC QLQ-C30 and the Functional Assessment of Cancer Therapy – General (FACT-G) measured different aspects of quality of life and should be independently used. Testing psychometric properties of the EORTC QLQ-C30 in heterogeneous diagnostic group yield similar results as found in homogeneous group. These results support that the EORTC QLQ-C30 (version 3.0) has proven to be a reliable and valid measure of the quality of life in Thai patients with various types of cancer.     

Unidimensional 12-Item Zarit Caregiver Burden Interview for the Assessment of Dementia Caregivers’ Burden Obtained by Item Response Theory

ObjectivesTo develop a one-dimensional version of the 22-item Zarit Caregiver Burden Interview (ZBI) by applying item response theory approaches.MethodsThe answers to the 22-item ZBI of 241 caregivers participating in a clinical trial were analyzed 1) with a Mokken nonparametric item response theory analysis to ascertain the dimensional structure underlying the scale and obtain a one-dimensional reduced version, 2) with the Samejima’s graded response model to assess the item characteristics of the reduced version, and 3) with confirmatory factor analysis to confirm the unidimensionality of the reduced ZBI version and assess the item loadings to the burden latent variable.ResultsMokken analysis resulted in a major one-dimensional scale comprising 12 items directly related with burden. All items showed scalability indices over 0.30. The scalability for the overall scale was 0.44 defining a medium scale according to Mokken’s criteria. An unconstrained Samejima’s graded response model showed appropriate fit, and most items of the reduced 12-item ZBI presented pertinent difficulty and discrimination parameters. The results of the 12-item ZBI confirmatory factor analysis fitted to a one-dimensional latent structure for burden (comparative fit index=0.975; root-mean-square error of approximation=0.067; weighted root mean square residual=0.677). All factor lodgings were above 0.40 with items 9 (strained by the relative) and 22 (overall feeling of burden) presenting the highest loadings.ConclusionsThe reduced 12-item ZBI fits a one-dimensional latent variable of burden. Further psychometric studies, focusing on its equivalence for different populations, sensitivity to change, and minimal important difference are warranted.