Systematic review of outcome domains and instruments used in designs of clinical trials for interventions that seek to restore bilateral and binaural hearing in adults with unilateral severe to profound sensorineural hearing loss (‘single-sided deafness’)

Background: This systematic review aimed to identify, compare and contrast outcome domains and outcome
instruments reported in studies investigating interventions that seek to restore bilateral (two-sided) and/or binaural
(both ears) hearing in adults with single-sided deafness (SSD). Findings can inform the development of evidence-based guidance to facilitate design decisions for confirmatory trials.

Methods: Records were identified by searching MEDLINE, EMBASE, PubMed, CINAHL,, ISRCTN,
CENTRAL, WHO ICTRP and the NIHR UK clinical trials gateway. The search included records published from 1946 to
March 2020. Included studies were those as follows: (a) recruiting adults aged 18 years or older diagnosed with SSD
of average threshold severity worse than 70 dB HL in the worse-hearing ear and normal (or near-normal) hearing in
the better-hearing ear, (b) evaluating interventions to restore bilateral and/or binaural hearing and (c) enrolling
those adults in a controlled trial, before-and-after study or cross-over study. Studies that fell just short of the
participant eligibility criteria were included in a separate sensitivity analysis.

Results: Ninety-six studies were included (72 full inclusion, 24 sensitivity analysis). For fully included studies, 37
exclusively evaluated interventions to re-establish bilateral hearing and 29 exclusively evaluated interventions to
restore binaural hearing. Overall, 520 outcome domains were identified (350 primary and 170 secondary). Speech-related outcome domains were the most common (74% of studies), followed by spatial-related domains (60% of
studies). A total of 344 unique outcome instruments were reported. Speech-related outcome domains were
measured by 73 different instruments and spatial-related domains by 43 different instruments. There was
considerable variability in duration of follow-up, ranging from acute (baseline) testing to 10 years after the
intervention. The sensitivity analysis identified no additional outcome domains.

Conclusions: This review identified large variability in the reporting of outcome domains and instruments in
studies evaluating the therapeutic benefits and harms of SSD interventions. Reports frequently omitted information
on what domains the study intended to assess, and on what instruments were used to measure which domains.


Roulla Katiri, Deborah A. Hall, Catherine F. Killan, Sandra Smith, Pattarawadee Prayuenyong and Pádraig T. Kitterick


Journal: Trials
Volume: 22
Issue: 220
Pages: -
Year: 2021
DOI: 10.1186/s13063-021-05160-5

Further Study Information

Current Stage: Completed
Date: March 2018 - March 2021
Funding source(s): National Institute for Health Research (NIHR)

Health Area

Disease Category: Ear, nose, & throat

Disease Name: Single Sided Deafness (SSD), Unilateral Hearing Loss

Target Population

Age Range: 18 - 100

Sex: Either

Nature of Intervention: Other, Procedure, Device

Stakeholders Involved

Study Type

- Systematic review of outcome measures/measurement instruments
- Systematic review of outcomes measured in trials


- Systematic review