1. Risk of bias assessment table.

Domain	Risk of bias judgement
Selection bias	Low	High	Unclear
Random sequence generation	Assigned if simple randomisation was used (e.g. computer‐generated random sequence, coin tossing).	Assigned if study reported an inadequate randomisation method (e.g. using date of birth or odd/even numbers).	Assigned if there was insufficient detail to judge the risk of bias as low or high.
	Assigned if restricted randomisation was used (e.g. block randomisation, provided that within groups randomisation was not affected).
Allocation Concealment	Assigned if there was evidence of concealed allocation sequence in which allocations could not have been foreseen in advance of, or during, enrolment.	Assigned if those enrolling participants were aware of the group (or period in a cross‐over trial) to which the next enrolled participant would be allocated.	Assigned if there was insufficient detail to judge the risk of bias as low or high.
Detection bias	Low	High	Unclear
Blinding of outcome assessors (blinding of participants and facilitators is not possible in psychosocial interventions).	Assigned if outcome assessors were blind to treatment allocation.	Assigned if the outcome assessors were aware of treatment allocation (e.g. if the cognitive stimulation group leader was also an outcome assessor).	Assigned if there was insufficient detail to judge the risk of bias as low or high.
Attrition bias	Low	High	Unclear
Incomplete outcome data	Assigned if the study reported levels of attrition, reasons for attrition and how missing data were dealt with. Assigned if the impact of missing data was not believed to alter the conclusions and there were acceptable reasons for the missing data.	Assigned if there was inadequate information regarding the level of attrition in each group, reasons for attrition and if missing data were not handled correctly.	Assigned if there was insufficient detail to judge the risk of bias as low or high.
Reporting bias	Low	High	Unclear
Selective reporting	Assigned if study reported results of all outcome measures that were detailed in the methods section. If a study protocol was available, low risk of bias was assigned if the outcome assessments reported in the trial paper matched those detailed in the protocol.	Assigned if study did not report results of all outcome measures that were detailed in the methods section. Assigned if all outcome measures detailed in the protocol (if available) were not reported in the study.	Assigned if there was insufficient detail to judge the risk of bias as low or high.
Other bias	Low	High	Unclear
Availability of training and supervision	Assigned if cognitive stimulation sessions were facilitated by people who had received some form of training to ensure the necessary principles of cognitive stimulation were adhered to. The definition of training was inclusive and could range from a brief session to a longer, more intensive course. This also applied to interventions delivered by trained family carers. The opportunity for facilitators to access appropriate supervision was also desirable.	Assigned if there was no evidence of facilitator training or supervision.	Assigned if there was insufficient detail to judge the risk of bias as low or high.
Availability of manual, structure or protocol	Assigned if there was evidence of a documented intervention protocol, structure or manual outlining the content of each session to ensure the principles of cognitive stimulation were adhered to.	Assigned if there was no evidence of a treatment protocol, structure or manual for facilitators to follow.	Assigned if there was insufficient detail to judge the risk of bias as low or high.