Perestelo‐Perez 2016.

Study characteristics
Methods	Cluster‐randomised trial, parallel group (1:1)
Participants	Patients from primary care centres in Tenerife, Spain Unit of randomisation: clinician Study aim: to assess the efficacy of the statin choice decision aid compared to usual primary care in Spanish participants with type 2 diabetes mellitus Inclusion criteria: 18 years of age or older, type 2 diabetes mellitus, Spanish language‐speaking, and no cognitive or sensorial impairments Exclusion criteria: no additional criteria listed Total randomised at baseline: 29 physicians with 168 participants (n = 15 physicians with 86 participants in intervention group, n = 14 physicians with 82 participants in the comparison group) Mean age (SD): intervention 63.9 years (9.7) and control 59.6 years (12.3); sex: intervention 41% women, control 34% women; 100% diabetes mellitus; 10‐year risk category: intervention 37.6% high risk, control 25.3% high risk; ischaemic heart disease: intervention 24%, control 18%
Interventions	Intervention group: statin choice decision aid about the use of statins. The decision aid consisted of a 3‐page pamphlet listing: CVD risk factors, 10‐year CVD risk based on the UKPDS risk engine presented in pictographs with and without statins, list of adverse effects of statins and their incidence Comparison group: usual care
Outcomes	Primary and secondary outcomes not specified Outcomes reported: statin knowledge, risk perception, decisional conflict scale (DCS), satisfaction with decision‐making, problem areas in diabetes questionnaire, self‐report of statin taking, self‐report of adherence at 3 months (Morisky), consultation time by physician Follow‐up: immediately after encounter and at 3 months Total analysed at 3 months follow‐up: 131 participants (n = 67 intervention, n = 64 comparison)
Study funding sources	Spanish Ministry of Health, Social Services and Equality (grant number: EC10‐005)
Notes	Analyses of outcomes accounted for clustering, but no power calculations performed. Significant baseline differences between intervention and control groups. At 3 months, 20% of participants were lost to follow‐up (but 42% missing data for adherence outcome). ITT analysis not performed Study funded by Spanish Ministry of Health, Social Services and Equality (grant number: EC10‐005) No conflicts of interest reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Physicians who consented to participate were randomised to intervention or usual care by means of a computer‐generated list."
Allocation concealment (selection bias)	High risk	Participants were recruited to the trial by clinicians and this occurred after clinicians were randomised Significant baseline difference between the 2 treatment groups suggests high risk of selection bias. Participants in the intervention group were significantly older, had more hypertension, and were more likely to be prescribed statins at baseline than participants in the control group
Blinding of participants and personnel (performance bias) All outcomes	High risk	Participants and clinicians not blinded to intervention
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported by authors but all outcomes were measured by participant self‐report
Incomplete outcome data (attrition bias) All outcomes	High risk	34/168 (20%) participants were lost to follow‐up. Adherence data were missing for 71/168 (42%) participants. ITT analysis not performed
Selective reporting (reporting bias)	High risk	Per clinical trial registration, the primary outcome was adherence at 3 months as measured by Morisky scale, chart abstraction, and pharmacy records. This was not reported as a primary outcome by the authors and the latter 2 methods were not used to measure adherence Several secondary outcomes not reported: haemoglobin A1c, lipid profile, health‐related quality of life, consultation time
Other bias	High risk	Small study bias