Minimally detectable change and minimal clinically important difference of a decline in sentence intelligibility and speaking rate for individuals with amyotrophic lateral sclerosis

Purpose: The purpose of this study was to determine the formula: MDC₉₅ = 1.96 × √2 × SEM. For estimation of the minimally detectable change (MDC) and minimal clinically MCID, receiver operating characteristic curves were important difference (MCID) of a decline in speech sentence generated, and area under the curve and optimal thresholds intelligibility and speaking rate for individuals with amyotrophic to maximize sensitivity and specificity were calculated. lateral sclerosis (ALS). We also examined how the MDC Results: The MDC for sentence intelligibility was 12.07%, and MCID vary across severities of dysarthria. and the MCID was 1.43%. The MDC for speaking rate Method: One-hundred forty-seven patients with ALS and was 36.57 WPM, and the MCID was 8.80 WPM. Both MDC 49 healthy control subjects were selected from a larger, and MCID estimates varied with severity of dysarthria. longitudinal study of bulbar decline in ALS, resulting in Conclusions: The findings suggest that declines greater a total of 650 observations. Intelligibility and speaking than 12% sentence intelligibility and 37 WPM are rate in words per minute (WPM) were calculated using the required to be outside measurement error and that these Sentence Intelligibility Test (Yorkston, Beukelman, & Hakel, estimates vary widely across dysarthria severities. 2007), and the ALS Functional Rating Scale–Revised The MDC and MCID metrics used in this study to detect (Cedarbaum et al., 1999) was administered to capture real and clinically relevant change should be estimated patient perception of motor impairment. The MDC at the for other measures of speech outcomes in intervention 95% confidence level was estimated using the following research.