Hetlevik 1999.

Study characteristics
Methods	Cluster‐randomised controlled trial, parallel group (1:1)
Participants	People with hypertension from 29 primary care health centres in Sor and Nord‐Trondelag counties in Norway Unit of randomisation: health centre Number recruited: 29 health centres and 2239 participants total (n = 17 health centres with 984 participants in the intervention group; n = 12 health centres with 1255 participants in the comparison group) Mean age: 64 years, 58% women, 100% Norwegian
Interventions	Intervention group: Computerised clinical decision support software with risk scores and guideline‐based treatment recommendations Educational seminars Audit and feedback Comparison group: usual care
Outcomes	Outcomes measured: last registered cholesterol, blood pressure, weight (or BMI), number of cigarettes Risk score calculated only if enough information available during the search period Number analysed at 18 month follow‐up: n = 887 intervention, n = 1127 comparison Number analysed after 3 month extension (21 month follow‐up): n = 879 intervention, n = 1119 comparison Follow‐up: 18 months initially, trial extended 3 months due to missing data
Study funding sources	Norwegian Medical Association with contribution from the foundation promoting general practice in Sor‐Trondelag
Notes	Issues with intervention fidelity: "After 18 months the CDSS had been used, partly or totally, in the treatment of 104 patient in the intervention group." Trial extended by 3 months because of inadequate collection of data at 18 months
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method of random sequence generation not reported
Allocation concealment (selection bias)	Unclear risk	Method of allocation concealment not reported
Blinding of participants and personnel (performance bias) All outcomes	High risk	Personnel not blinded, and not clear that participants were blinded
Blinding of outcome assessment (detection bias) All outcomes	High risk	Outcomes abstracted by primary investigator who was not blinded
Incomplete outcome data (attrition bias) All outcomes	High risk	> 90% of participants in both groups were missing data to calculate 10‐year CHD risk at 18 months. The trial was extended by 3 months which decreased this amount to ~ 50%
Selective reporting (reporting bias)	Unclear risk	No protocol available for review
Other bias	High risk	Trial extended by 3 months due to missing data. Clinicians provided lists of missing participant information and were asked to resolve this. Poor intervention fidelity (CDSS was used partially or totally in the treatment of only 104 participants in the intervention group)