Item Response Theory Model for Functional Assessment of Spinal Muscular Atrophy Based on the Hammersmith Functional Motor Scale Expanded
Objective To establish an item response theory(IRT)model for functional assessment of spinal muscular atrophy based on the Hammersmith functional motor scale expanded(HFMSE).Methods A total of 23 patients with SMA treated with cor-rective treatment in the Department of Geriatric Neurology and Pediatrics of the First Affiliated Hospital of Nanjing Medical Univer-sity from February 2021 to June 2023 were included.Stack design was used to construct item response models(IRMs)for repeated measurement data.The likelihood ratio was used to calculate the parameters of the discrimination degree,guessing degree,difficulty and patient ability level(θ)of the HFMSE items for the optimal model.Differential test functioning(DTF)was used to analyze whether the scale was biased by rehabilitation treatment or gender.Monte Carlo simulation was used to prove that the difficulty dis-tribution of the model items was not affected by the sampling process,a person-item plot was drawn according to the median expect-ed difficulty,and the differences of the difficulty of each item in the HFMSE scale and the patient ability levels between the first as-sessment and the follow-up assessment were also discussed.Results A total of 32 items were included in this study to construct four alternative models,of which the 3 parameter logistic model(3PLM)had the best goodness of fit(P>0.05,M2 statistic=479.75).The caution degree of all items was 1 in 3PLM,and the discrimination degree,guessing degree and difficulty of the items were cal-culated.The model had no significant evaluation bias on the factors of gender and rehabilitation treatment.The results showed high reliability(Cronbach's α=0.955,LCRC=0.981)and validity[θ value was positively correlated with the original total score(r=0.99,P<0.001)]of 3PLM,allowing conversion of the θ value of the patient's ability to total score of the scale by binomial transformation.A person-item plot showing the distribution of item parameters and individual parameters on the patient ability level(θ)scale was used to observe the relationship between θ values and item difficulties.Conclusion IRT model based on HFMSE can provide sugges-tions on functional assessment and decision-making in rehabilitation treatment for patients with SMA in different scenarios,but at-tention should be paid to its item guessing degree.
spinal muscular atrophyHammersmith functional motor scale expandeditem response theoryfunctional analysis
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