Some theoretical considerations concerning the relation between functional gain and insertion gain.

Three examples in which insertion gain and functional gain measures of hearing aid response do not agree are illustrated. In two of the cases, functional gain measures overestimate the true real-ear gain for average conversational speech and in the third example, insertion gain measures are shown to provide an inaccurate estimate of aided benefit. Reasons for these discrepancies are discussed, and an alternative method for measuring real-ear hearing-aid response is described.