How to Efficiently Measure the Intelligibility of People With Parkinson's Disease

The purpose of this study was to determine the most efficient approaches to measuring the intelligibility of people with Parkinson's disease (PD) when considering the estimation method, listener experience, number of listeners, number of sentences, and the ways these factors may interact.

Speech-language pathologists (SLPs) and inexperienced listeners estimated the intelligibility of people with and without PD using orthographic transcription or a visual analog scale (VAS). Intelligibility estimates were based on 11 Speech Intelligibility Test sentences. We simulated all combinations of listeners and sentences to compare intelligibility estimates based on fewer listeners and sentences to a speaker-specific benchmark estimate based on the mean intelligibility across all sentences and listeners.

Intelligibility estimates were closer to the benchmark (i.e., more accurate) when more listeners and sentences were included in the estimation process for transcription- and VAS-based estimates and for SLPs and inexperienced listeners. Differences between the benchmark and subset-based intelligibility estimates were, in some cases, smaller than the minimally detectable change in intelligibility for people with PD.

The intelligibility of people with PD can be measured more efficiently by reducing the number of listeners and/or sentences, up to a point, while maintaining the ability to detect change in this outcome. Clinicians and researchers may prioritize either fewer listeners or fewer sentences, depending on the specific constraints of their work setting. However, consideration must be given to listener experience and estimation method, as the effect of reducing the number of listeners and sentences varied with these factors.