Criteria of Candidacy for Unilateral Cochlear Implantation in Postlingually Deafened Adults I: Theory and Measures of Effectiveness

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Abstract
The objectives of this study were to distinguish the equivalent-effectiveness, health-economic, and actuarial approaches to specifying criteria of candidacy for medical interventions; to apply the equivalent-effectiveness approach to unilateral cochlear implantation for postlingually deafened adults; and to determine whether the criterion should take age at implantation and duration of profound deafness into account. The study was designed as a prospective cohort study in 13 hospitals with four groups of severely-profoundly hearing-impaired subjects distinguished by their preoperative ability to identify words in sentences when aided acoustically. The groups represent a progressive relaxation of criteria of candidacy: Group I (N=134) scored 0% correct without lipreading and did not improve their lipreading score significantly when aided; group II (N=93) scored 0% without lipreading but did improve their lipreading score significantly when aided; group III (N=53) scored 0% without lipreading when the to-be-implanted ear was aided but between 1% and approximately 50% when the other ear was aided. Group IV (N=31) scored between 1% and approximately 50% without lipreading when the to-be-implanted ear was aided. Measures of speech intelligibility, health utility, and otologically relevant quality of life were obtained before surgery and 9 mo after surgery from each subject. Measures of effectiveness were calculated as the difference between 9-mo and preoperative scores. Effectiveness differed only slightly between groups. Effectiveness was not strongly associated with age at the time of implantation. Greater effectiveness was associated with implantation in the ear with the shorter duration of profound deafness. Cochlear implantation was least effective when the preoperative audiological status of the better-hearing ear was good and the duration of profound deafness of the implanted ear was long. As a result, effectiveness was not significant for the subsets of groups III and IV, who were given implants in ears that had been profoundly deaf for more than 30 yr. The effectiveness of cochlear implantation differs little between groups of candidates who score zero with acoustic hearing aids before surgery and groups who score up to approximately 50% correct, thereby justifying a relaxation of the criterion of candidacy to embrace some members of the latter groups. The criterion should be based not only on preoperative speech intelligibility but also on duration of profound deafness in the to-be-implanted ear.