Humes and Krull (2012) note many questions still need to be answered with regard to measuring the effectiveness of hearing aids in adults.
For example, regarding “what” to measure, there are at least three types of “what” measures: (1) self-reported measures of benefit or satisfaction are important, (2) self-reported usage, and (3) aided speech understanding across “representative listening conditions.”
Further, “when” to measure is important, too. Humes and Krull note that “valid and reliable communication-related hearing aid outcome measures, such as aided speech understanding, can be obtained at four to six weeks post fit….” Humes and Krull report self-reported benefit and satisfaction may require three to six months of listening experience before outcomes would be expected to stabilize.
Humes and Krull state that “benefaction” (i.e., benefit and/or satisfaction) measures indicate significant reductions with regard to hearing handicap and/or the frequency of hearing loss related problems as people with hearing loss transition from unaided to aided conditions.
Typical usage measures indicate hearing aid use of four to eight hours daily (or “about three-quarters” of the time) and importantly, speech understanding was also significantly improved from unaided to aided test conditions—except in extremely loud acoustic environments with very poor signal-to-noise ratios (SNRs). The authors note, "...more research needs to be conducted regarding the effectiveness of hearing aids in adults...."
For More Information, References, and Recommendations
Humes L, Krull V. (2012) Hearing Aids for Adults. In Evidence Based Practice in Audiology - Evaluating Interventions for Children and Adults With Hearing Impairment. Eds. Wong and Hickson. Chapter Four, Pages 61-92.