Modification indices for the 2-PL and the nominal response model

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Objective. To evaluate the contribution of assessing forefoot joints to the measurement range and measurement precision of joint counts in early rheumatoid arthritis (RA) using item response theory. Methods. Baseline measures of tender and swollen joint counts were analyzed in 459 early RA patients from the Dutch Rheumatoid Arthritis Monitoring remission induction cohort. The contribution of forefoot joints was studied by evaluating their effect on the measurement range and measurement precision of measures based on 28-joint counts. In addition, the alignment between the patient and joint distributions was investigated to determine whether the forefoot joints were informative for measuring joint tenderness or swelling of an early RA patient. Results. In total, 233 patients (50.76%) experienced tenderness and 200 patients (43.57%) experienced swelling in >1 forefoot joint. Forefoot joints were more informative for measuring joint tenderness than joint swelling, but did not significantly improve the measurement range and measurement precision of the 28-joint counts. Furthermore, including forefoot joints did not remove the existing discrepancy between the joint and patient distributions in both joint counts. Conclusion. Forefoot joints were frequently affected on an individual level, but did not significantly improve the measurement range or precision of 28-joint counts in patients with early RA. From a measurement perspective, reduced joint counts are appropriate for use on a population level. The contribution of assessing forefoot joints on an individual level requires further investigation. Additionally, the results should be cross-validated in patients with longer disease durations to determine whether the pattern of joint involvement is similar in later stages of RA.

Section: Methodsmentioning

confidence: 99%

Contribution of assessing forefoot joints in early rheumatoid arthritis patients: Insights from item response theory

Siemons¹,

Klooster²,

Taal³

et al. 2013

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“…The rationale of this test was to partition the latent PF continuum into a number of segments and to evaluate whether the item characteristic curve of an item conformed to the form predicted by the model in each of these segments (9). These statistics can be used to identify misfitting items and together provide a test of overall model fit.…”

Section: Significance and Innovationsmentioning

confidence: 99%

Crosscultural Measurement Equivalence of the Health Assessment Questionnaire II

Voshaar

Glas

Klooster

et al. 2013

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Objective. To evaluate the crosscultural measurement equivalence of the US and Dutch Health Assessment Questionnaire II (HAQ-II) in rheumatoid arthritis (RA). Methods. Item response theory (IRT) analyses were performed on US (n ‫؍‬ 18,747) and Dutch (n ‫؍‬ 1,022) HAQ-II data to evaluate the equivalence of crosscultural item performance. The observed inconsistencies were modeled by assigning country-specific item parameters to biased items. The impact of crosscultural item bias on the comparability of the Dutch and US total scores was analyzed by evaluating the agreement between physical function levels estimated from an IRT model with country-specific item parameters for biased items and physical function levels estimated from the original model that did not account for cultural bias. Results. Two items showed significant crosscultural bias. However, the agreement in physical function estimates between the respecified and original models was very high, with an intraclass correlation coefficient >0.99 and Bland-Altman limits of agreement ranging from ؊0.08 to ؊0.01 on a latent scale with a mean of 0 and an SD of 1. Conclusion. This study suggests that the Dutch and US HAQ-II produce total scores that can be interpreted interchangeably across countries in RA studies, despite some minor bias at the item level.

“…In this model, both time points are represented by distinct, correlated dimensions, and patients are described by 2 timepoint specific structural damage scores (u T1 and u T2 ), but the item parameters are constrained to be equal over time so that each joint is characterized by 1 International Classification of Functioning, Disability, and Health category that traces the probability that structural damage is present as a function of u. To evaluate the fit of this model, Lagrange Multiplier statistics and accompanying effect-size statistics were obtained, described in detail elsewhere (11). Essentially, the Lagrange Multiplier test evaluates whether item parameters are invariant across the subsample of patients with low, medium, and high total scores.…”

Section: Methodsmentioning

confidence: 99%

Further Simplification of the Simple Erosion Narrowing Score With Item Response Theory Methodology

Voshaar

Schenk

Klooster

et al. 2016

Objective. To further simplify the simple erosion narrowing score (SENS) by removing scored areas that contribute the least to its measurement precision according to analysis based on item response theory (IRT) and to compare the measurement performance of the simplified version to the original. Methods. Baseline and 18-month data of the Combinatietherapie Bij Reumatoide Artritis (COBRA) trial were modeled using longitudinal IRT methodology. Measurement precision was evaluated across different levels of structural damage. SENS was further simplified by omitting the least reliably scored areas. Discriminant validity of SENS and its simplification were studied by comparing their ability to differentiate between the COBRA and sulfasalazine arms. Responsiveness was studied by comparing standardized change scores between versions. Results. SENS data showed good fit to the IRT model. Carpal and feet joints contributed the least statistical information to both erosion and joint space narrowing scores. Omitting the joints of the foot reduced measurement precision for the erosion score in cases with below-average levels of structural damage (relative efficiency compared with the original version ranged 35-59%). Omitting the carpal joints had minimal effect on precision (relative efficiency range 77-88%). Responsiveness of a simplified SENS without carpal joints closely approximated the original version (i.e., all D standardized change scores were 0.06). Discriminant validity was also similar between versions for both the erosion score (relative efficiency 5 97%) and the SENS total score (relative efficiency 5 84%). Conclusion. Our results show that the carpal joints may be omitted from the SENS without notable repercussion for its measurement performance.