Estimating thresholds for walking independence after stroke: a comparison of item response and classical test theories

BACKGROUND: Item response theory (IRT), particularly the graded response model, provides a latent trait (θ) that reflects balance ability and offers a complementary framework for psychometric evaluation. Although IRT is recommended for estimating clinical thresholds, its application to cutoff determination for stroke populations remains limited. We hypothesized that IRT-based approaches will yield cutoff values that differ from those derived using classical test theory and provide additional methodological insight for cutoff determination. PURPOSE: To estimate and compare cutoff values for walking independence in inpatients with stroke using classical test theory and IRT. METHODS: Data from 165 inpatients with stroke were analyzed. Balance was assessed using the Brief Balance Evaluation Systems Test (Brief-BESTest). Cutoff scores were calculated using receiver operating characteristic (ROC), IRT combined with ROC (IRT+ROC), prevalence-based IRT method (old IRT), and embedded state-item IRT method (new IRT). Discriminative performance was evaluated using area under the ROC curve (AUC), sensitivity, specificity, likelihood ratios, and accuracy. RESULTS: The cutoff values for walking independence were 12.37 (ROC), 11.46 (IRT+ROC), 10.54 (old IRT), and 7.90 (new IRT). All methods demonstrated comparable performance, with AUC values ranging from 0.769 to 0.794, indicating good discriminative ability of the Brief-BESTest for identifying walking independence. The new IRT method achieved the highest AUC and sensitivity; ROC and IRT+ROC methods achieved similar AUCs. Although cutoff values and classification metrics differed slightly across methods, their confidence intervals overlapped. CONCLUSION: To our knowledge, this is the first study to directly compare cutoff estimation methods incorporating IRT in stroke rehabilitation, suggesting that IRT-based approaches can yield cutoff values with stability comparable to that of classical test theory and providing methodological insight for future research and clinical assessment scale development.