Volpp 2015.

Study characteristics
Methods	A randomized controlled trial of negative co‐payments: the CHORD trial RCT (NA clusters and NA providers), conducted in 1) Study participants were drawn from patients at 3 hospitals in Pennsylvania: the Philadelphia Veterans Affairs Medical Center (PVAMC), the Veterans Administration Pittsburgh Health Care System (VAPitt), and the Pinnacle Health clinic in Harrisburg. 2) Intervention led by study staff and involved financial incentive and/or computerised behavioural intervention (CBI). In United States of America. 2 arms: 1. Control (control group and CBI group) (control arm) and 2. Intervention (financial incentive (FI) group and FI + CBI group) (intervention arm)
Participants	Control arm N: 92.99 Intervention arm N: 89.10, NA, NA Diabetes type: 4 Mean age: 60.97 ± 9.75 % Male: 80.75 Longest follow‐up: 12 months
Interventions	Control arm: (control group and CBI group) 1) Patient education Intervention arm: (financial incentive (FI) group and FI + CBI group) 1) Patient education 2) Financial Incentives
Outcomes	Systolic blood pressure
Funding source	The work in this paper was primarily supported by a grant from the Commonwealth of Pennsylvania, titled Collaboration to Reduce Disparities in Hypertension, grant number ME‐02‐382. Supplemental support was received from Pfizer, Inc.
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation was carried out using a random number generator.
Allocation concealment (selection bias)	Low risk	Allocation assignments were concealed, with staff unable to access randomisation assignment for each participant until all eligibility criteria were entered in an electronic tracking system and consent forms were completed.
Patient's baseline characteristics (selection bias)	Unclear risk	Table 1. There were significantly more blacks in the control group (P = 0.01) and age has a P value of 0.05, but no data only for diabetes patients.
Patient's baseline outcomes (selection bias)	Unclear risk	Table 1. P values above 0.05 for blood pressure and medication taking, but no data only for diabetes patients.
Incomplete outcome data (attrition bias)	High risk	Overall, they lost 20.2% of patients at 12 months, 23.7% in the control group and 16.5% in the intervention group. High and unbalanced numbers. Reasons not reported. No data only for diabetes patients.
Blinding of participants and personnel (performance bias) and of outcome assessors (detection bias)	Low risk	Our outcome of interest was objectively measured (SBP).
Selective reporting (reporting bias)	Unclear risk	Prospectively registered protocol. They report DBP data for all patients after the intervention but not for diabetic patients only, as they did for SBP. They did not do cost analysis as stated in the protocol. They also measured adherence using the medication possession ratio in the paper, but this was not included in the protocol. Protocol mentions reporting blood pressure at 6 and 12 months, only reported at 12 months.
Risk of contamination (other bias)	Low risk	Both groups had computerised behavioural intervention (CBI, patient education), but that was planned.
Other bias	High risk	For the analysis, they merged 2 groups to make the intervention group (financial incentive and financial incentive + CBI) and they merged 2 other groups to make the control group (control and CBI).