Table 1.

Aim, duration and procedures of phases used in the schedule of reinforcement

Phase	Aim and rationale	Duration	Procedure
Baseline	Provides baseline data to evaluate changes in CO during the intervention period Serves as training for study monitoring procedures	Up to 5 days	Samples to be submitted once daily Average CO level calculated from results Provision of baseline samples will not be incentivised
Shaping	Provides incentives for intermediate criteria between tobacco smoking and abstinence Improves treatment effectiveness while fostering learning and reinforcement prior to quitting100 This phase is optional for those not wishing to stop smoking immediately	Up to 4 weeks	Weekly reduction of CO targets will be calculated using baseline CO levels and the estimated number of weeks until target abstinence Incentives for smoking reductions are based on a fixed schedule of $A2.50 per verified sample, with two submissions per day permitted (morning and afternoon) Participants are encouraged to set a quit date within 4 weeks of study enrolment
Abstinence	Provides an incentive for every verified sample indicating a CO of ≤5 ppm High-frequency monitoring is required in the early stages of a quit attempt. Any smoking during the initial weeks of abstinence is predictive of negative long-term smoking outcomes in general populations and pregnant women101 102 Higher magnitude incentives are provided for abstinence as these exert more influence over behavioural change than those of lower magnitude103	Period from post baseline or reduction phase through to commencement of thinning phase	Incentives start at $A3.00, increasing by $A0.10 for every verified negative and are capped at $A20.00. Escalating schedules of reinforcement induce longer periods of continuous abstinence than fixed schedules104 105 Samples to be provided twice daily (defined as 24:00 till 23:59) separated by a minimum of 8 hours70 for the initial 4 weeks of non-smoking. After this time, they will reduce to once daily
Thinning	Reduce incentives for abstinence and monitoring requirements The switch from continuous to intermittent reinforcement has been shown to reduce reliance on incentives and to prolong abstinence106	4 weeks prior to expected delivery date	Samples to be completed every second day at varying time points to verify abstinence Due to varying treatment length, this will only apply to those who have been abstinent for 6 weeks (defined as completion of 4 weeks of twice daily + 2 weeks of once-daily CO samples)
Contingency reset	Incentives will not be provided for missed samples or those >5 ppm and the value of subsequent samples <6 ppm will be reduced To encourage abstinence after relapse, incentive values can be reset after a period of abstinence71 76		Following a positive sample, the reinforcement value of the next negative CO sample will be reset to its initial rate ($A3.00) Two consecutive negative samples will revert the incentive to its pre-reset value

CO, carbon monoxide; ppm, parts per million.