Item response theory and factor analysis as a mean to characterize occurrence of response shift in a longitudinal quality of life study in breast cancer patients

Patient-reported outcomes and symptom clusters pattern of chemotherapy-induced toxicity in patients with early breast cancer

OBJECTIVE

This study aims to characterize patient-reported chemotherapy-induced toxicity in patients with breast cancer, determine its association with treatment regimens and patient characteristics, identify toxicity symptom clusters within a specific chemotherapy timeframe and analyze the correlation between symptom clusters within and between the timeframe to understand the changes and influences across chemotherapy.

METHODS

Forty-six patient-reported toxicities during neoadjuvant/adjuvant chemotherapy for breast cancer were evaluated using adapted CTCAE version 4.0. Chi-Square/Fisher's Exact test was performed to analyze the difference in the incidence of toxicity symptoms by chemotherapy regimens. Poisson regression performed to assess factors associated with patient's total chemotherapy toxicity. Exploratory factor analysis (EFA) conducted to identify symptom clusters at T1 (first half) and T2 (second half of planned cycle). Factor scores were generated and Spearman correlation performed to explore the factor scores correlation between symptom clusters.

RESULTS

A total of 142 patients with stage I-III breast cancer were included. The incidence of several toxicities differed significantly among three chemotherapy regimens. Subjects age ≥51 years are associated with lower number of reported toxicity (IRR/incidence rate ratio = 0.94, 95% confidence interval/CI 0.88 to 0.99, p = 0.042). Receiving more chemotherapy cycles are associated with higher number of reported toxicity (IRR = 1.06, 95% CI 1.03 to 1.10, p<0.001). Two symptom clusters identified at T1 (psychoneurological-pain/PNP-T1 and gastrointestinal-psychological/GIP-T1 cluster) and three at T2 (psychoneurological-pain/PNP-T2, epithelial/EPI-T2, and gastrointestinal cluster/GI-T2), with moderate-strong positive correlation between PNP-T1 and GIP-T2 (p<0.001), PNP-T1 and PNP-T2 (p<0.001), and GIP-T1 and PNP-T2 (p<0.001).

CONCLUSIONS

This study investigated 46 patient-reported toxicities prospectively during adjuvant/neoadjuvant chemotherapy for early breast cancer. Anthracycline-taxane combination regimen had higher proportions of toxicity incidence. Subject's age and number of chemotherapy cycles significantly associated with total number of toxicity symptoms. Two symptom clusters at T1 and three at T2 were identified, with significant correlation between symptom clusters within and between chemotherapy timeframe.

Response shift results of quantitative research using patient-reported outcome measures: a descriptive systematic review

PURPOSE

The objective of this systematic review was to describe the prevalence and magnitude of response shift effects, for different response shift methods, populations, study designs, and patient-reported outcome measures (PROM)s.

METHODS

A literature search was performed in MEDLINE, PSYCINFO, CINAHL, EMBASE, Social Science Citation Index, and Dissertations & Theses Global to identify longitudinal quantitative studies that examined response shift using PROMs, published before 2021. The magnitude of each response shift effect (effect sizes, R-squared or percentage of respondents with response shift) was ascertained based on reported statistical information or as stated in the manuscript. Prevalence and magnitudes of response shift effects were summarized at two levels of analysis (study and effect levels), for recalibration and reprioritization/reconceptualization separately, and for different response shift methods, and population, study design, and PROM characteristics. Analyses were conducted twice: (a) including all studies and samples, and (b) including only unrelated studies and independent samples.

RESULTS

Of the 150 included studies, 130 (86.7%) detected response shift effects. Of the 4868 effects investigated, 793 (16.3%) revealed response shift. Effect sizes could be determined for 105 (70.0%) of the studies for a total of 1130 effects, of which 537 (47.5%) resulted in detection of response shift. Whereas effect sizes varied widely, most median recalibration effect sizes (Cohen's d) were between 0.20 and 0.30 and median reprioritization/reconceptualization effect sizes rarely exceeded 0.15, across the characteristics. Similar results were obtained from unrelated studies.

CONCLUSION

The results draw attention to the need to focus on understanding variability in response shift results: Who experience response shifts, to what extent, and under which circumstances?

Detection of response shift in health-related quality of life studies: a systematic review

Background

Response Shift (RS) refers to the idea that an individual may undergo changes in its health-related quality of life (HRQOL). If internal standard, values, or reconceptualization of HRQOL change over time, then answer to the same items by the same individuals may not be comparable over time. Traditional measures to evaluate RS is prone to bias and strong methodologies to study the existence of this phenomenon is required. The objective is to systematically identify, analyze, and synthesize the existing and recent evidence of statistical methods used for RS detection in HRQOL studies.

Methods

The analysis of selected studies between January 2010 and July 2020 was performed through a systematic review in MEDLINE/PubMed, Scopus, Web of Science, PsycINFO and Google Scholar databases. The search strategy used the terms “Health-Related Quality of Life” and “Response Shift” using the filters “Humans”, “Journal Article”, “English” and “2010/01/01–2020/07/31”. The search was made in August 2020.

Results

After considering the inclusion and exclusion criteria, from the total selected articles (675), 107 (15.9%) of the publications were included in the analysis. From these, 79 (71.0%) detected the existence of RS and 86 (80.4%) only used one detection method. The most used methods were Then Test (n = 41) and Oort’s Structural Equation Models (SEM) (n = 35). Other method used were Multiple Lineal Regression (n = 7), Mixed-Effect Regression (n = 6), Latent Trajectory Analysis (n = 6), Item Response Theory (n = 6), Logistics Regression (n = 5), Regression and Classification Trees (n = 4) and Relative Importance Method (n = 4). Most of these detected recalibration, including Then Test (n = 27), followed by Oort’s SEM that detected the higher combination of RS types: recalibration (n = 24), reprioritization (n = 13) and reconceptualization (n = 7).

Conclusions

There is a continuous interest of studying RS detection. Oort’s SEM becomes the most versatile method in its capability for detecting RS in all different types. Despite results from previous systematic reviews, same methods have been used during the last years. We observed the need to explore other alternative methods allowing same detection capacity with robust and highly precise methodology. The investigation on RS detection and types requires more study, therefore new opportunity grows to continue attending this phenomenon through a multidisciplinary perspective.

Giving meaning to patient reported outcomes in breast reconstruction after mastectomy - A systematic review of available scores and suggestions for further research

Background

There are three patient reported outcome measure instruments (PROMs) that have adequate content validity for breast reconstruction, BREAST-Q, BRECON-31 and EORTC QLQ-BRECON-23, and they all have been robustly validated. The aim of this study was to systematically review scores giving meaning to validated PROMs for breast reconstruction after mastectomy and discuss methods to enable interpretation of them.

Methods

A systematic review was performed according to the recommendations of PRISMA. Prospero CRD42021255874. Included articles had to meet criteria defined in a SPIDER (Sample, Phenomenon of Interest, Design, Evaluation, Research type). The included studies were critically appraised using the GRADE approach.

Results

Three articles were finally included in the review: two studies on scores for healthy controls and one on minimally important differences (MIDs), both of BREAST-Q. All of the studies were performed in North America. Only MIDs based on statistical characteristics, and not on what constitutes a relevant change for the patient, exist. The risk of bias was evaluated as very high and moderate, respectively, of inconsistencies as low, of indirectness as high, of imprecisions as low, and of publication bias as probably low.

Conclusions

The overall certainty of evidence for scores giving meaning to PROMs for breast reconstruction is low (GRADE ƟƟОО). More studies are needed to establish relevant healthy control scores and what constitutes a relevant clinical difference for patient-reported outcome measures for breast reconstruction after mastectomy. Clinical implications of the findings and suggestions for further research are suggested in the article.

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Patient reported outcome measurements have to be clinically interpretable to make sense.

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Three articles on scores giving meaning to PROMs for breast reconstruction post-mastectomy exist.

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More studies are needed to establish relevant controls and clinical differences in scores.

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Clinical implications and suggestions for further research are discussed.

Initiatives for education, training, and dissemination of morbidity assessment and reporting in a multiinstitutional international context: Insights from the EMBRACE studies on cervical cancer

In 2008, the GEC ESTRO Gyn network launched the first multiinstitutional, observational, and prospective international study on MRI-guided brachytherapy in locally advanced cervical cancer patients (EMBRACE-I). EMBRACE-I was followed by EMBRACE-II from 2016 and ongoing. Among the aims of the EMBRACE studies are to benchmark morbidity outcomes and develop dose-volume effects and predictive models for morbidity. The EMBRACE studies collect both physician (CTCAE v.3) and patient (EORTC QLQ-C30/CX24) reported outcomes, including baseline information, in a regular follow-up schedule. The EMBRACE studies feature high numbers of patients (EMBRACE-I N = 1416, EMBRACE-II N = 1500 expected) enrolled from many institutions worldwide (EMBRACE-I n = 23, EMBRACE-II n = 45). This large-scale multiinstitutional approach offers a unique opportunity to investigate and develop new strategies for improving the quality of assessment and reporting of morbidity. This report presents an overview of the challenges and pitfalls regarding the assessment and reporting of morbidity encountered during more than a decade of development and research activities within the EMBRACE consortium. This includes the recognition and evaluation of inconsistencies in the morbidity assessment, and consequently, the provision of assistance and training in the scoring procedure to reduce systematic assessment bias. In parallel, a variety of methodological approaches were tested to comprehensively summarize morbidity outcomes, and a novel approach was developed to refine dose-effect models and risk factor analyses. The purpose of this report is to present an overview of these findings, describe the learning process, and the strategies that have consequently been implemented regarding educational activities, training, and dissemination.

Disease-specific quality of life following a flare in systemic lupus erythematosus: an item response theory analysis of the French EQUAL cohort

OBJECTIVE

To explore, at an item-level, the effect of disease activity (DA) on specific health-related quality of life (HRQoL) in SLE patients using an item response theory longitudinal model.

METHODS

This prospective longitudinal multicentre French cohort EQUAL followed SLE patients over 2 years. Specific HRQoL according to LupusQoL and SLEQOL was collected every 3 months. DA according to SELENA-SLEDAI flare index (SFI) and revised SELENA-SLEDAI flare index (SFI-R) was evaluated every 6 months. Regarding DA according to SFI and each SFI-R type of flare, specific HRQoL of remitting patients was compared with non-flaring patients fitting a linear logistic model with relaxed assumptions for each domain of the questionnaires.

RESULTS

Between December 2011 and July 2015, 336 patients were included (89.9% female). LupusQoL and SLEQOL items related to physical HRQoL (physical health, physical functioning, pain) were most affected by musculoskeletal and cutaneous flares. Cutaneous flares had significant influence on self-image. Neurological or psychiatric flares had a more severe impact on specific HRQoL. Patient HRQoL was impacted up to 18 months after a flare.

CONCLUSION

Item response theory analysis is able to pinpoint items that are influenced by a given patient group in terms of a latent trait change. Item-level analysis provides a new way of interpreting HRQoL variation in SLE patients, permitting a better understanding of DA impact on HRQoL. This kind of analysis could be easily implemented for the comparison of groups in a clinical trial.

TRIAL REGISTRATION

ClinicalTrials.gov, http://clinicaltrials.gov, NCT01904812.

How peoples’ ratings of dental implant treatment change over time?

Objectives

Dental implant treatment (DIT) improves peoples’ oral health-related quality of life (OHQoL). Assessment of longitudinal changes in OHRQoL may be undermined by response shift (RS). RS is the process by which quality of life changes, independent of health status as a result recalibration, reprioritization or reconceptualization. Thus, this study aimed to describe RS in the OHRQoL and perceived oral health of individuals receiving DIT and to compare the then-test, a self-anchored scale and the classification and regression trees (CRT) approaches for assessing RS.

Methods

OHRQoL was assessed in 100 patients receiving DIT using the OHIP-Edent (n = 100) and a self-anchored scale (n = 45) before placement of the final restoration and 3 to 6 months after treatment was completed. The OHIP-Edent was also used as a retrospective assessment at follow-up. CRT examined changes in the OHIP-Edent total score as a dependent variable with global changes in oral health and each OHIP-Edent subscale score as independent variables.

Results

OHRQoL and perceived oral health improved after treatment. The OHIP-Edent score decreased from 36.4 at baseline to 12.7 after treatment. On average, participants recalibrated their internal standard downwards (− 4.0 OHIP-Edent points). CRT detected downwards recalibration in 5% of participants and upwards in 15%. Reprioritization was observed in the social disability and psychological discomfort aspects of OHRQoL.

Conclusions

RS affects longitudinal assessments of OHRQoL in DIT, reducing the apparent magnitude of change. The then-test and CRT are valid and complementary methods to assess RS.

Comparison of structural equation modelling, item response theory and Rasch measurement theory-based methods for response shift detection at item level: A simulation study

When assessing change in patient-reported outcomes, the meaning in patients’ self-evaluations of the target construct is likely to change over time. Therefore, methods evaluating longitudinal measurement non-invariance or response shift at item-level were proposed, based on structural equation modelling or on item response theory. Methods coming from Rasch measurement theory could also be valuable. The lack of evaluation of these approaches prevents determining the best strategy to adopt. A simulation study was performed to compare and evaluate the performance of structural equation modelling, item response theory and Rasch measurement theory approaches for item-level response shift detection. Performances of these three methods in different situations were evaluated with the rate of false detection of response shift (when response shift was not simulated) and the rate of correct response shift detection (when response shift was simulated). The Rasch measurement theory-based method performs better than the structural equation modelling and item response theory-based methods when recalibration was simulated. Consequently, the Rasch measurement theory-based approach should be preferred for studies investigating only recalibration response shift at item-level. For structural equation modelling and item response theory, the low rates of reprioritization detection raise issues on the potential different meaning and interpretation of reprioritization at item-level.

The Role of Response-Shift in Studies Assessing Quality of Life Outcomes Among Cancer Patients: A Systematic Review

Objective: Response-shift has been cited as an important measurement consideration when assessing patient reported quality of life (QoL) outcomes over time among patients with severe chronic conditions. Here we report the results of a systematic review of response shift in studies assessing QoL among cancer patients.

Methods: A systematic review using MEDLINE, EMBASE, and PsychINFO along with a manual search of the cited references of the articles selected, was conducted. A quality review was performed using STROBE criteria and reported according to PRISMA guidelines.

Results: A systematic review of 1,487 records published between 1,887 and December 2018 revealed 104 potentially eligible studies, and 35 studies met inclusion criteria for content and quality. The most common cancer patient populations investigated in these studies were breast (18 studies), lung (14 studies), prostate (eight studies), and colorectal (eight studies). Response shift was identified among 34 of the 35 studies reviewed. Effect sizes were reported in 17 studies assessing QoL outcomes among cancer patients; 12 of which had negligible to small effect sizes, four reported medium effect sizes which were related to physical, global QoL, pain, and social (role) functioning and one reported a large effect size (fatigue). The most prevalent method for assessing response shift was the then-test, which is prone to recall bias, followed by the pre-test and post-test method. Given the heterogeneity among the characteristics of the samples and designs reviewed, as well as the overall small to negligible effect sizes for the effects reported, conclusions stating that changes due to internal cognitive shifts in perceived QoL should account for changes observed in cancer patients' QoL outcomes should be interpreted with caution.

Conclusion: Further work is needed in this area of research. Future studies should control for patient characteristics, time elapsed between diagnosis and baseline assessment and evaluate their contribution to the presence of response shift. Time between assessments should include short and longer periods between assessments and evaluate whether the presence of response shift holds over time. Possible avenues for inquiry for future investigation are discussed.

Determining clinically important differences in health-related quality of life in older patients with cancer undergoing chemotherapy or surgery

PURPOSE

Using the EORTC Global Health Status (GHS) scale, we aimed to determine minimal clinically important differences (MCID) in health-related quality of life (HRQOL) changes for older cancer patients with a geriatric risk profile, as defined by the geriatric 8 (G8) health screening tool, undergoing treatment. Simultaneously, we assessed baseline patient characteristics prognostic for HRQOL changes.

METHODS

Our analysis included 1424 (G8 ≤ 14) older patients with cancer scheduled to receive chemotherapy (n = 683) or surgery (n = 741). Anchor-based methods, linking the GHS score to clinical indicators, were used to determine MCID between baseline and follow-up at 3 months. A threshold of 0.2 standard deviation (SD) was used to exclude MCID estimates too small for interpretation. Logistic regressions analysed baseline patient characteristics prognostic for HRQOL changes.

RESULTS

The 15-item Geriatric Depression Scale (GDS15), Visual Analogue Scale (VAS) for Fatigue and ECOG Performance Status (PS) were selected as clinical anchors. In the surgery group, MCID estimates for improvement and deterioration were ECOG PS (5*, 11*), GDS15 (5*, 2) and VAS Fatigue (3, 9*). In the chemotherapy group, MCID estimates for improvement and deterioration were ECOG PS (8*, 7*), GDS15 (5, 4) and VAS Fatigue (5, 5*). Estimates with * were > 0.2 SD threshold. Patients experiencing pain or malnutrition (surgery group) or fatigue (chemotherapy group) at baseline showed a significantly stable or improved HRQOL (p < 0.05) after their treatment.

CONCLUSION

The reported MCID for improvement and deterioration depended on the anchor used and treatment received. The estimates can be used to evaluate significant changes in HRQOL and to determine sample sizes in clinical trials.

Scoping review of response shift methods: current reporting practices and recommendations

BACKGROUND

Response shift (RS) has been defined as a change in the meaning of an individual's self-evaluation of his/her health status and quality of life. Several statistical model- and design-based methods have been developed to test for RS in longitudinal data. We reviewed the uptake of these methods in patient-reported outcomes (PRO) literature.

METHODS

CINHAHL, EMBASE, Medline, ProQuest, PsycINFO, and Web of Science were searched to identify English-language articles about RS published until 2016. Data on year and country of publication, PRO measure adopted, RS detection method, type of RS detected, and testing of underlying model assumptions were extracted from the included articles.

RESULTS

Of the 1032 articles identified, 101 (9.8%) articles were included in the study. While 54.5 of the articles reported on the Then-test, 30.7% of the articles reported on Oort's or Schmitt's structural equation modeling (SEM) procedure. Newer RS detection methods, such as relative importance analysis and random forest regression, have been used less frequently. Less than 25% reported on testing the assumptions underlying the adopted RS detection method(s).

CONCLUSIONS

Despite rapid methodological advancements in RS research, this review highlights the need for further research about RS detection methods for complex longitudinal data and standardized reporting guidelines.

An assessment of quality of life for early phase after adjuvant radiotherapy in breast cancer survivors: a Korean multicenter survey (KROG 14-09)

BACKGROUNDS

Quality of life (QoL) has become a major concern as the survival time of breast cancer increases. We investigated the changes in QoL through comprehensive categorical analysis, for the first three years after breast cancer treatment including radiotherapy.

METHODS

A total of 1156 patients were enrolled from 17 institutions. All survivors were grouped according to a surveillance period of 9-15 months (first year), 21-27 months (second year), and 33-39 months (third year) from the end of radiotherapy. The 5-dimensional questionnaire by the EuroQol group (EQ-5D) and the EORTC Quality of Life Questionnaire; breast cancer specific module (QLQ-BR23) were checked by self-administrated method.

RESULTS

First, second and third year groups comprised 51.0, 28.9, and 21.0%. In EQ-5D-3 L (3-Likert scale) analysis, pain/discomfort and anxiety/depression categories showed lower QoL. In multivariate analyses of EQ-5D-VAS (visual-analogue scale), categories of pain/discomfort and self-care were improved with time; axillary dissection was a significant clinical factor deteriorates pain/discomfort, self-care and usual activities. In QLQ-BR23 analysis, the lowest scored category was sexual activity, followed by sexual enjoyment, future perspective, and hair loss, and the best scored category was breast symptoms. In multivariate analyses, arm symptoms, breast symptoms and body image were improved with time.

CONCLUSIONS

Categories of pain/discomfort and self-care in EQ-5D-VAS, arm/breast symptoms and body image in QLQ-BR23 were improved, while categories of anxiety/depression and future perspective BR23 were not, suggesting necessity of psychosocial support. This research provides comprehensive information on the categorical aspects of QoL and changes during early follow-up after breast cancer treatment.

Impact of the occurrence of a response shift on the determination of the minimal important difference in a health-related quality of life score over time

Background

An important challenge of the longitudinal analysis of health-related quality of life (HRQOL) is the potential occurrence of a Response Shift (RS) effect. While the impact of RS effect on the longitudinal analysis of HRQOL has already been studied, few studies have been conducted on its impact on the determination of the Minimal Important Difference (MID). This study aims to investigate the impact of the RS effect on the determination of the MID over time for each scale of both EORTC QLQ-C30 and QLQ-BR23 questionnaires in breast cancer patients.

Methods

Patients with breast cancer completed the EORTC QLQ-C30 and the EORTC QLQ-BR23 questionnaires at baseline (time of diagnosis; T0), three months (T1) and six months after surgery (T2). Four hospitals and care centers participated in this study: cancer centers of Dijon and Nancy, the university hospitals of Reims and Strasbourg At T1 and T2, patients were asked to evaluate their HRQOL change during the last 3 months using the Jaeschke transition question. They were also asked to assess retrospectively their HRQOL level of three months ago.

The occurrence of the RS effect was explored using the then-test method and its impact on the determination of the MID by using the Anchor-based method.

Results

Between February 2006 and February 2008, 381 patients were included of mean age 58 years old (SD = 11). For patients who reported a deterioration of their HRQOL level at each follow-up, an increase of RS effect has been detected between T1 and T2 in 13/15 dimensions of QLQ-C30 questionnaire, and 4/7 dimensions of QLQ-BR23 questionnaire. In contrast, a decrease of the RS effect was observed in 8/15 dimensions of QLQ-C30 questionnaire and in 5/7 dimensions of QLQ-BR23 questionnaire in case of improvement. At T2, the MID became ≥ 5 points when taking into account the RS effect in 10/15 dimensions of QLQ-C30 questionnaire and in 5/7 dimensions of QLQ-BR23 questionnaire.

Conclusions

This study highlights that the RS effect increases over time in case of deterioration and decreases in case of improvement. Moreover, taking the RS into account produces a reliable and significant MID.

Electronic supplementary material

The online version of this article (doi:10.1186/s12955-016-0569-5) contains supplementary material, which is available to authorized users.

Making space for empathy: supporting doctors in the emotional labour of clinical care

Background

The academic and medical literature highlights the positive effects of empathy for patient care. Yet, very little attention has been given to the impact of the requirement for empathy on the physicians themselves and on their emotional wellbeing.

Discussion

The medical profession requires doctors to be both clinically competent and empathetic towards the patients. In practice, accommodating both requirements can be difficult for physicians. The image of the technically skilful, rational, and emotionally detached doctor dominates the profession, and inhibits physicians from engaging emotionally with their patients and their own feelings, which forms the basis for empathy. This inhibition has a negative impact not only on the patients but also on the physicians. The expression of emotions in medical practice is perceived as unprofessional and many doctors learn to supress and ignore their feelings. When facing stressful situations, these physicians are more likely to suffer from depression and burnout than those who engage with and reflect on their feelings. Physicians should be supported in their emotional work, which will help them develop empathy. Methods could include questionnaires that aid self-reflection, and discussion groups with peers and supervisors on emotional experiences. Yet, in order for these methods to work, the negative image associated with the expression of emotions should be questioned. Also, the work conditions of physicians should improve to allow them to make use of these tools.

Summary

Empathy should not only be expected from doctors but should be actively promoted, assisted and cultivated in the medical profession.

Applying the Longitudinal Model from Item Response Theory to Assess Health-Related Quality of Life in the PRODIGE 4/ACCORD 11 Randomized Trial

INTRODUCTION

A new longitudinal statistical approach was compared to the classical methods currently used to analyze health-related quality-of-life (HRQoL) data. The comparison was made using data in patients with metastatic pancreatic cancer.

METHODS

Three hundred forty-two patients from the PRODIGE4/ACCORD 11 study were randomly assigned to FOLFIRINOX versus gemcitabine regimens. HRQoL was evaluated using the European Organization for Research and Treatment of Cancer (EORTC) QLQ-C30. The classical analysis uses a linear mixed model (LMM), considering an HRQoL score as a good representation of the true value of the HRQoL, following EORTC recommendations. In contrast, built on the item response theory (IRT), our approach considered HRQoL as a latent variable directly estimated from the raw data. For polytomous items, we extended the partial credit model to a longitudinal analysis (longitudinal partial credit model [LPCM]), thereby modeling the latent trait as a function of time and other covariates.

RESULTS

Both models gave the same conclusions on 11 of 15 HRQoL dimensions. HRQoL evolution was similar between the 2 treatment arms, except for the symptoms of pain. Indeed, regarding the LPCM, pain perception was significantly less important in the FOLFIRINOX arm than in the gemcitabine arm. For most of the scales, HRQoL changes over time, and no difference was found between treatments in terms of HRQoL.

DISCUSSION

The use of LMM to study the HRQoL score does not seem appropriate. It is an easy-to-use model, but the basic statistical assumptions do not check. Our IRT model may be more complex but shows the same qualities and gives similar results. It has the additional advantage of being more precise and suitable because of its direct use of raw data.