Nonignorable data in IRT models: Polytomous responses and response propensity models with covariates

Missing data usually present special problems for statistical analyses, especially when the data are not missing at random, that is, when the ignorability principle defined by Rubin (1976) does not hold. Recently, a substantial number of articles have been published on model-based procedures to handle nonignorable missing data due to item nonresponse (Holman & Glas, 2005; Glas & Pimentel, 2008; Rose, von Davier & Xu, 2010; Pohl, Grӓfe & Rose, 2014). In this approach, an item response theory (IRT) model for the observed data is estimated concurrently with an IRT model for the propensity of the missing data. The present article elaborates on this approach in two directions. Firstly, the preceding articles only consider dichotomously scored items; in the present article it is shown that the approach equally works for polytomously scored items. Secondly, it is shown that the methods can be generalized to allow for covariates in the model for the missing data. Simulation studies are presented to illustrate the efficiency of the proposed methods

The AMC Linear Disability Score in patients with newly diagnosed Parkinson disease

Objective: The aim of this study was to examine the clinimetric properties of the AMC Linear Disability Score (ALDS), a new generic disability measure based on Item Response Theory, in patients with newly diagnosed Parkinson disease (PD).\ud \ud Methods: A sample of 132 patients with PD was evaluated using the Hoehn and Yahr (H&Y), the Unified PD Rating Scale motor examination, the Schwab and England scale (S&E), the Short Form–36, the PD Quality of Life Questionnaire, and the ALDS.\ud \ud Results: The internal consistency reliability of the ALDS was good ([alpha] = 0.95) with 55 items extending the sufficient item-total correlation criterion (r > 0.20). The ALDS was correlated with other disability measures (r = 0.50 to 0.63) and decreasingly associated with measures reflecting impairments (r = 0.36 to 0.37) and mental health (r = 0.23 to -0.01). With regard to know-group validity, the ALDS indicated that patients with more severe PD (H&Y stage 3) were more disabled than patients with mild (H&Y stage 1) or moderate PD (H&Y stage 2) (p < 0.0001). The ALDS discriminated between more or less severe extrapyramidal symptoms (p = 0.001) and patients with postural instability showed lower ALDS scores compared to patients without postural instability (p = < 0.0001). Compared to the S&E (score 100% = 19%), the ALDS showed less of a ceiling effect (5%).\ud \ud Conclusion: The AMC Linear Disability Score is a flexible, feasible, and clinimetrically promising instrument to assess the level of disability in patients with newly diagnosed Parkinson disease

Modern psychometrics applied in rheumatology - a systematic review

Background Although item response theory (IRT) appears to be increasingly used within health care research in general, a comprehensive overview of the frequency and characteristics of IRT analyses within the rheumatic field is lacking. An overview of the use and application of IRT in rheumatology to date may give insight into future research directions and highlight new possibilities for the improvement of outcome assessment in rheumatic conditions. Therefore, this study systematically reviewed the application of IRT to patient-reported and clinical outcome measures in rheumatology. Methods Literature searches in PubMed, Scopus and Web of Science resulted in 99 original English-language articles which used some form of IRT-based analysis of patient-reported or clinical outcome data in patients with a rheumatic condition. Both general study information and IRT-specific information were assessed. Results Most studies used Rasch modeling for developing or evaluating new or existing patient-reported outcomes in rheumatoid arthritis or osteoarthritis patients. Outcomes of principle interest were physical functioning and quality of life. Since the last decade, IRT has also been applied to clinical measures more frequently. IRT was mostly used for evaluating model fit, unidimensionality and differential item functioning, the distribution of items and persons along the underlying scale, and reliability. Less frequently used IRT applications were the evaluation of local independence, the threshold ordering of items, and the measurement precision along the scale. Conclusion IRT applications have markedly increased within rheumatology over the past decades. To date, IRT has primarily been applied to patient-reported outcomes, however, applications to clinical measures are gaining interest. Useful IRT applications not yet widely used within rheumatology include the cross-calibration of instrument scores and the development of computerized adaptive tests which may reduce the measurement burden for both the patient and the clinician. Also, the measurement precision of outcome measures along the scale was only evaluated occasionally. Performed IRT analyses should be adequately explained, justified, and reported. A global consensus about uniform guidelines should be reached concerning the minimum number of assumptions which should be met and best ways of testing these assumptions, in order to stimulate the quality appraisal of performed IRT analyses

Bayesian Analysis of Heterogeneous Residual Variance in Canine Behaviour

Non-additive effects like for instance genotype-environment interactions and genetically structured heterogeneity of residual variance are notoriously dependent on scale: many statistical non-additive phenomena disappear after a careful choice of transformation of the phenotypic values. Particularly for behavioural measures, scale is a delicate matter. We present a novel Bayesian approach that assesses heterogeneity in environmental variance as a function of genetic effects, where the scale is defined by a psychometric model based on item-response theory. This makes analysis results independent of what items are in a particular test version. We apply the method to fearful behaviour in dogs and compare results with the more usual sum score approac

Acceptance of new technology: a usability test of a computerized adaptive test for fatigue in rheumatoid arthritis

Background: Little is known about the acceptance and usability of computerized adaptive tests (CATs) among patients with rheumatoid arthritis (RA). The main difference between completing a CAT and a traditional questionnaire concerns item presentation. CATs only provide one item at a time on the screen, and skipping forward or backward to review and change already given answers is often not possible. Objective: The objective of this study was to examine how patients with RA experience a Web-based CAT for fatigue. Methods: In individual sessions, participants filled in the CAT while thinking aloud, and were subsequently interviewed about their experience with the new instrument. The technology acceptance model (TAM) was used to structure the results. Results: The participants were 15 patients with RA. They perceived the CAT as clear, brief, and easy to use. They were positive about answering one question per screen, the changing response options, layout, progress bar, and item number. There were 40% (6/15) of the participants that also mentioned that they experienced the completion of the CAT as useful and pleasant, and liked the adaptive test mechanism. However, some participants noted that not all items were applicable to everybody, and that the wordings of questions within the severity dimension were often similar. Conclusions: Participants perceived the “CAT Fatigue RA” as easy to use, and also its usefulness was expressed. A 2.0 version has been improved according to the participants’ comments, and is currently being used in a validation study before it will be implemented in daily clinical practice. Our results give a first indication that CAT methodology may outperform traditional questionnaires not merely on measurement precision, but also on usability and acceptance valuation

How age and sex affect the erythrocyte sedimentation rate and C-reactive protein in early rheumatoid arthritis

BACKGROUND: The erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are two commonly used measures of inflammation in rheumatoid arthritis (RA). As current RA treatment guidelines strongly emphasize early and aggressive treatment aiming at fast remission, optimal measurement of inflammation becomes increasingly important. Dependencies with age, sex, and body mass index have been shown for both inflammatory markers, yet it remains unclear which inflammatory marker is affected least by these effects in patients with early RA. METHODS: Baseline data from 589 patients from the DREAM registry were used for analyses. Associations between the inflammatory markers and age, sex, and BMI were evaluated first using univariate linear regression analyses. Next, it was tested whether these associations were independent of a patient's current disease activity as well as of each other using multiple linear regression analyses with backward elimination. The strengths of the associations were compared using standardized beta (beta) coefficients. The multivariate analyses were repeated after 1 year. RESULTS: At baseline, both the ESR and CRP were univariately associated with age, sex, and BMI, although the association with BMI disappeared in multivariate analyses. ESR and CRP levels significantly increased with age (beta-ESR = 0.017, p < 0.001 and beta-CRP = 0.009, p = 0.006), independent of the number of tender and swollen joints, general health, and sex. For each decade of aging, ESR and CRP levels became 1.19 and 1.09 times higher, respectively. Furthermore, women demonstrated average ESR levels that were 1.22 times higher than that of men (beta = 0.198, p = 0.007), whereas men had 1.20 times higher CRP levels (beta = -0.182, p = 0.048). Effects were strongest on the ESR. BMI became significantly associated with both inflammatory markers after 1 year, showing higher levels with increasing weight. Age continued to be significantly associated, whereas sex remained only associated with the ESR level. CONCLUSIONS: Age and sex are independently associated with the levels of both acute phase reactants in early RA, emphasizing the need to take these external factors into account when interpreting disease activity measures. BMI appears to become more relevant at later stages of the disease

Towards an integrated testing service system

In a testing service system (TSS) the activities that play a role in educational and psychological assessment are integrated and, as far as possible, computerized. Such systems will be the basis for test design, administration, analysis, and reporting in the next century. The main activities in a Testing Service System are item banking, item construction, test assembly, test administration, test analysis, and calibration. Testing service systems exist in various forms, ranging from general-purpose software packages to systems especially developed to support specific organizations and the administration of specific tests. With the advent of Windows technology, both individual professionals and testing organizations are more and more in a position to create a tailor-made TSS by linking existing software elements that have the functionality suited to the demands of the situation. In this paper, a number of the considerations that play a role in designing a TSS are described