Test–Retest Reliability Bounds for Consonant-Nucleus-Consonant Word and Phoneme Scores for Cochlear-Implant Users

OBJECTIVES: This report establishes test-retest 95% confidence interval bounds for consonant-vowel-consonant (CNC) word- and phoneme-recognition scores for cochlear-implant listeners. DESIGN: Data from two published cochlear-implant studies were analyzed. Across-list SDs for individual subjects were compared with the expected SD for a binomially distributed variable. The model was adjusted by tuning the effective binomial distribution set size to minimize the root-mean-square deviation from measured SDs. RESULTS: The effective CNC-word set size equaled the number of words per list (50). The effective phoneme set size (approximately 100) was lower than the number of phonemes per list (150). CONCLUSIONS: Results support the hypotheses that individual CNC words are recognized independently, and that there is mutual information across phonemes, resulting in a smaller effective set size. A table of confidence intervals and critical-difference values for CNC word and phoneme recognition is provided.