Measurement of functional mobility in multiple sclerosis: A crosswalk between the patient-determined disease steps and the Neuro-QoL Lower Extremity Function—Short Form

Background The Patient-Determined Disease Steps (PDDS) and Neuro-QoL Lower Extremity Function—Short Form (Neuro-QoL LEF-SF) are patient-reported outcome measures used to monitor mobility symptoms in multiple sclerosis (MS). Objective To develop and validate a crosswalk between the PDDS and Neuro-QoL LEF-SF. Methods Using equipercentile equating, we created a crosswalk from a training sample of 619 MS patients (mean PDDS = 2.4 ± 2.3; mean Neuro-QoL LEF-SF = 33.0 ± 8.3). Validation was performed in a separate sample of 147 MS patients (mean PDDS = 0.6 ± 1.2; mean Neuro-QoL LEF-SF = 38.9 ± 2.8). Agreement between original and converted scores was evaluated using paired t-tests and concordance correlation coefficients. Results PDDS and Neuro-QoL LEF-SF scores were strongly correlated in both training (r = −0.89) and validity (r = −0.76) samples. No significant differences in change scores were observed. Concordance coefficients of original and converted scores supported good to very good agreement. Conclusion We developed a crosswalk for the conversion of scores between the PDDS and the Neuro-QoL LEF-SF for patients with MS. Evidence for the preliminary validity of this crosswalk was demonstrated with both the initial training sample and a separate validity sample. This crosswalk facilitates score comparisons and data harmonization across studies and clinical registries using either measure.