*3.2. Quality Assessment of Included Studies*

The critical appraisal can be found in Tables 1 and 2 for studies where tinnitus was the primary complaint and those where tinnitus was not the primary complaint, respectively.

In studies where tinnitus was the primary complaint, only one study [58] defined appropriately its inclusion criteria. The remaining studies either did not provide information on contralateral ear [59] or included moderate hearing loss thresholds for inclusion criteria [54,55,60–62]. In addition, in several studies, the efficacy of conventional treatments was not tested before CI [56,63–68]. When selecting participants, inclusion and exclusion criteria were not well defined [55]. Two out of fourteen studies were retrospective [55,64]. Blinding was applied in only one study [62]. The population samples of two studies overlapped and the criteria for recruiting additional participants were not well defined [54,56]. The process of cochlear implantation and rehabilitation was not clear in all studies [60,64,67]. The intervention protocol was either unreported [55,58,59,63,64] or did not respect standard process [56,59,61,62,65,67]. Missing data, participant dropouts and withdrawal exceeding 10% [54,58,65] were justified in only one study [58].


**Table 1.** Quality assessment of studies in which tinnitus was the primary complaint.

PCS: prospective cohort study; RCS: retrospective cohort study, CR: Case report. Confounding: O = no confounding (use of three inclusion criteria: SSD defined with (PTA (0.5, 1, 2, 4 kHz) > 70 dBs in one ear and <30 dBs in the other ear, severe tinnitus defined by TFI > 32, THI > 58, TQ > 42, VAS loudness or annoyance > 6/10, and failure of conventional treatment such as CROS, BCD, HA), • = inclusion criteria not appropriately used, Ø = no information. Selection of participants (based on participant characteristics observed after the start of the intervention): O = no bias in selection of participants, • = bias in selection of participants, NA: not applicable. Classification of interventions: O = intervention status well defined before application (CI), • = intervention status defined retrospectively, Ø = no information. Deviation from intended intervention: O = standard cochlear implantation, activation and rehabilitation defined clearly in the protocol, • = deviations to the intervention protocol, Ø = no information. Missing data: O = < 10% missing data, • = ≥ 10% missing data, Ø = no information. Measurement of outcomes: O = similar measurement of outcomes between intervention groups AND blinding of the outcome assessors for intervention received by study participants, - = similar measurement of outcomes between intervention groups AND no blinding of the outcome assessors for intervention received by study participants, • = difference of measurement between groups AND no blinding of the outcome assessors for intervention received by study participants, NA: not applicable. Selection of reported results: O = primary outcomes reported according to the protocol, - = primary outcomes reported for all groups (no subset) and explanation if missing data, • = missing outcomes/data reported for a subset of measures, Ø: no information.

In studies where tinnitus was not the primary complaint, five studies defined appropriately its inclusion criteria [44,69–72]. When selecting participants, inclusion and exclusion criteria were not clearly provided [73,74], and blinding was not applied. Several studies were retrospective [71,72,74–76]. The CI intervention was not constantly described [57,77], and the majority of studies did not clarify if the standard CI protocol was adopted [44,69,71,72,74–76,78–81]. Missing data, participant dropouts and withdrawals exceeding 10% [71,74–76] were not constantly justified [75].


**Table 2.** Quality assessment of studies in which tinnitus was not the primary complaint.

PCS: prospective cohort study; RCS: retrospective cohort study, CR: Case report. Confounding: O = no confounding (use of three criteria: SSD defined with (PTA (0.5,1,2,4 kHz) > 70 dBs in one ear and <30 dBs in the other ear, and failure of conventional treatment such as CROS, BCD, HA), • = inclusion criteria not appropriately used. Selection of participants (based on participant characteristics observed after the start of the intervention): O = no bias in selection of participants, • = bias in selection of participants, NA: not applicable. Classification of interventions: O = intervention status well defined before application (CI), • = intervention status defined retrospectively, Ø = no information. Deviation from intended intervention: O = standard cochlear implantation, activation and rehabilitation defined clearly in the protocol, • = deviations to the intervention protocol, Ø = no information. Missing data: O = < 10% missing data, • = ≥10% missing data, Ø = no information. Measurement of outcomes: O = similar measurement of outcomes between intervention groups AND blinding of the outcome assessors for intervention received by study participants, - = similar measurement of outcomes between intervention groups AND no blinding of the outcome assessors for intervention received by study participants, • = difference of measurement between groups AND no blinding of the outcome assessors for intervention received by study participants, NA: not applicable. Selection of reported results: O = primary outcomes reported according to the protocol, - = primary outcomes reported for all groups (no subset) and explanation if missing data, • = missing outcomes/data reported for a subset of measures, Ø: no information.
