Twardella 2007.

Study characteristics
Methods	Randomised trial
Participants	General practitioners
Interventions	Financial incentive characteristics GPs were assured a financial remuneration of Euro 130 after study completion for each study participant they recruited who was "smoke free" at 12 months follow‐up. GPs could offer to their patients cost‐free prescriptions (up to Euro 130) for drugs proved effective in supporting smoking cessation. Type of intervention The practices were randomised into 4 experimental groups: Usual care (20 medical practices, 76 patients) Training + incentive (TI) (21 medical practices, 146 patients) Training + medication (TM) (21 medical practices, 144 patients) TI + TM (20 medical practices, 221 patients) Year 2002 to 2003, intervention happened in 2002
Outcomes	Patient outcome Self‐reported smoking abstinence obtained at 12 months follow‐up and validated by serum cotinine
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	The GPs participating in this trial were not a random selection but a selected group recruited from participants of a survey on promotion of smoking cessation. This group might be characterised by an increased commitment to the issue of smoking cessation and to improving their quality of cessation promotion.
Allocation concealment (selection bias)	High risk	Owing to the nature of the interventions, GPs and participants could not be blinded to the intervention.
Baseline outcome measurements similar	Unclear risk	The study has no baseline measure of outcome.
Baseline characteristics similar	Low risk	Participants did not differ substantially at baseline by intervention arm.
Incomplete outcome data (attrition bias) All outcomes	High risk	Missing outcome data likely to be related to true outcome. Reasons for the 13 withdrawals from the study were not given by the authors and were likely to be related to GP practices or patient characteristics.
Knowledge of the allocated interventions adequately prevented	Low risk	Blood samples collected in the follow‐up 12 months after recruitment were sent to a central laboratory, and cotinine levels in serum were determined in a blinded fashion by radio immunoassay, according to the manufacturer instructions (Immunodiagnostic, Bensheim, Germany).
Study adequately protected against contamination	Low risk	Allocation was by practice, and it is unlikely that the control group received the intervention.
Selective reporting (reporting bias)	Low risk	The outcomes mentioned in the methods section were reported in the results section.
Other bias	Low risk	No more information