Willner 2002.

Methods	Quasi‐randomised controlled trial (randomisation using alternate referrals) Setting: study conducted in the UK; community (participants recruited from community teams) Study dates are not provided
Participants	Inclusion criteria: presence of intellectual disability and problems with anger control 16 adults with intellectual disabilities were included (2 later dropped out); 8 participants in each group Mean age in treatment group 31.4; age range 18 ‐ 57; mean age in control group 30.4, age range 19 ‐ 55 Participants had mild to moderate level of intellectual disabilities (WAIS‐III/WAIS‐R)
Interventions	Treatment 1: 9 x 2‐hour group sessions Treatment was provided by psychologists/therapists Adherence to treatment/fidelity was not assessed Treatment 2: wait‐list control
Outcomes	Anger ratings by clients and carers at baseline, 3 weeks post‐treatment, and at 3 months follow‐up (intervention group only and therefore not included in the analysis) Measures included the Novacos Anger Scale and Provocation Inventory
Notes	No information in source of funding No declaration of conflicts of interest statement
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Randomisation was based on alternate referrals
Allocation concealment (selection bias)	High risk	No concealment of allocation as it was not possible
Blinding of participants and personnel (performance bias) All outcomes	High risk	No blinding of participants and personnel
Blinding of outcome assessment (detection bias) All outcomes	High risk	Quote: "it was not possible to arrange for assessments to be carried out independently or blind"
Incomplete outcome data (attrition bias) All outcomes	Low risk	2 participants were not included in the analysis. Quote: "one dropped out of the treatment group after the first session and the other, who was now in the control group, declined the post‐group assessment." The reasons for the dropout/missing data do not appear to be related to the outcome
Selective reporting (reporting bias)	Low risk	All prespecified outcomes were reported
Other bias	High risk	No published psychometric data on the instruments used