Dempster 1993.

Study characteristics
Methods	Single‐centre RCT with 11 months follow‐up Randomised by child for adenoidectomy; subsequently, 1 ear was randomly selected to receive a ventilation tube Data of relevance for this review are for the comparison of unilateral ventilation tube versus no treatment in ears of the same individual (either with no additional surgery, or with a background of adenoidectomy)
Participants	Location: UK, single centre Setting of recruitment and treatment: paediatric hospital clinic in Glasgow Study dates: August 1986 to February 1989 Sample size: Number randomised: 78 (number allocated to each group not reported) Number completed: 72 (37 with adenoidectomy, 35 without adenoidectomy) Participant (baseline) characteristics: Age, years, SD (range): Adenoidectomy (with and without VT) = 5.9 ± 1.4 (4 to 9) No adenoidectomy (with and without VT) = 5.7 ± 1.2 (4 to 9) Gender Adenoidectomy (with and without VT) = 17 males (46%), 20 females (54%) No adenoidectomy (with and without VT) = 23 males (66%), 12 females (34%) Inclusion criteria: Children aged between 3.5 and 12 years Otoscopic evidence of bilateral otitis media with effusion that satisfied the following criteria on 2 assessments, 12 weeks apart: (a) Pure tone air conduction thresholds average over 0.5 kHz, 1 kHz and 2 kHz of ≥ 25 dB HL (b) An air‐bone gap over 0.5 kHz, 1 kHz and 2 kHz of ≥ 15 dB (c) Type B tympanogram Exclusion criteria: Previous adenoidectomy or aural surgery Additional symptoms requiring surgical intervention, e.g. recurrent sore throat Cleft palate
Interventions	Intervention and comparisons Ventilation tube insertion: A unilateral Shah grommet was inserted following a radial myringotomy with aspiration of fluid Control group: The contralateral ear was not operated on The comparison was made between the ears of the same individual (operated versus un‐operated side). Note that half of the children in this trial also underwent adenoidectomy. For the purposes of this review, we have displayed the data from children who underwent adenoidectomy separately from those who did not undergo adenoidectomy. However, the data have been pooled together, to show the overall effect of ventilation tubes (with or without adenoidectomy).
Outcomes	Proportion of ears with hearing returned to normal Defined by the study authors as < 15 dB HL, using air conduction thresholds from pure tone audiometry Mean final hearing threshold (air conduction and air‐bone gap) Pure tone air conduction thresholds and air‐bone gap thresholds averaged over 0.5 kHz, 1 kHz and 2 kHz Mean change in hearing threshold Proportion of ears with persistence of OME Assessed using both otoscopy and tympanometry Adverse events: Proportion of ears with perforation/retraction Proportion of ears with tympanosclerosis Proportion of ears with tube not in situ
Funding sources	Not reported
Declarations of interest	No declaration is made
Notes	Research integrity checklist: No retraction notices identified Prospective registration not applicable (published before 2010) No excessive similarities in baseline characteristics Plausible loss to follow‐up reported No implausible results The number randomised to each group was not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No details provided on how the allocation sequence was generated.
Allocation concealment (selection bias)	Low risk	"These 78 children were then admitted to hospital within ten days and randomly allocated by a serially numbered envelope system..."
Blinding of participants and personnel (performance bias) All outcomes	High risk	No information provided on blinding of participants and personnel. There is a strong possibility that participants and personnel could identify which treatment a participant received and hence change their behaviour as a result.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	“At six and 12 months post‐surgery, the presence or absence of otitis media in the non‐grommeted ear was record by the validated otoscopist who was blind as to whether adenoidectomy had been performed and by tympanometry.” There was no report of blinding for either tympanometric or audiometric assessment. The outcomes are not sufficiently objective to discount the possibility of ascertainment bias.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	"Six children defaulted either at the six or 12 month assessment visits, leaving 72 (92 per cent) children with complete clinical, audiometric and tympanometric data for the pre‐operative and these post‐operative visits." Six of the 78 (8%) randomised children were lost to follow‐up. The distribution of those 6 across groups is not reported. Precise reasons for losses to follow‐up were not reported. It is therefore difficult to judge the potential for attrition bias.
Selective reporting (reporting bias)	Unclear risk	No protocol or trial registration was found. The published paper reports all expected outcomes.
Other bias	Unclear risk	It is unclear whether (for VT versus no treatment) comparisons were made within each individual child. The data are presented as if comparisons were made at whole trial arm level, as in a parallel‐group trial. There could therefore be a unit of analysis error, which could result in spuriously wide confidence intervals.