Table 1.

Planned family-based financial incentive intervention components.

Component	Description	Rationale
Intervention duration	•Six months.	•The relapse rate is usually relatively small after 6–12 months of abstinence [28].
Smoking status check-ins	•Cigarette smoking abstinence among index participants will be assessed and reinforced six times: weekly for four weeks, then at 3 and 6 months. •Both the index participant and enrolled family member will receive a $25 gift card for each smoking status check-in completed regardless of test results.	•Relapse occurs rapidly after a quit attempt, thus abstinence needs to be reinforced early on [28]. Sustained early smoking abstinence is predictive of long-term success [29]. Our incentive schedule will reinforce both initial and sustained cessation. •Remuneration for time for smoking status check-in completion may enhance retention of dyads.
Remote objective monitoring of smoking status	•Index participants will receive 1) the iCO™ Smokerlyzer®, a portable, handheld breath CO monitor that connects to a mobile device/tablet and 2) Alere™ iScreen mouth swab tests for cotinine. At each of the six smoking status check-ins, index participants will submit results to research staff via app or video call.	•Remote monitoring enhances intervention reach and scalability and allows for rapid biochemical testing proximal to obtaining self-reported smoking status.
Definition of verified cigarette smoking abstinence among index participants	•Self-reported cigarette smoking abstinence during the past 7 days with negative tests of breath CO (0–3 ppm) and saliva cotinine <30 ng/ml; or if NRT, e-cigarettes, or ST use is reported, with a positive cotinine test, the participant has a negative CO test.	•Reinforcement of abstinence is contingent on objective evidence of smoking abstinence. •Breath CO measurement can verify abstinence within the previous 24 h [30]. It is not confounded with detection of use of ST, NRT, or e-cigarettes because CO criterion for abstinence below 4–5 ppm provides better sensitivity and specificity for differentiating between those smoking and not smoking, and especially for comparing light smoking (<10 cpd) to heavier smoking [31,32]. •Cotinine is the major metabolite of nicotine and its presence in saliva indicates cigarette use in the past 6–7 days. Its specificity for cigarette smoking is excellent except for persons using nicotine-containing medications, ST, or e-cigarettes [30]. Thus, combining breath CO and cotinine measures is optimal.
Escalating incentive scheme and reward value	•Index participant will receive cash rewards for abstinence six times: $50, $75, $100, $125, $175, $225 (weekly for four weeks then at 3 and 6 months); maximum $750 total. •The enrolled family member will receive cash or non-cash rewards at the equivalent value earned by the index participant (maximum $750 total).	•Escalating reinforcement programs produce longer periods of smoking abstinence compared with constant rewards [33]. •Prior studies used total payment amounts ranging from $750-$1650 and all had similar effects on smoking abstinence. We chose the lowest value of $750 to enhance sustainability of the intervention while considering the context of the overall cost of living in Alaska, the seventh most expensive US state [34] and also taking into account the potential total combined incentive of $1500/dyad.
Immediacy of rewards	•We will pay rewards as soon as smoking status check-ins are completed, using text messages to notify each dyad participant of the reward earned. We will use a reloadable credit card for prompt payment of financial rewards to index participants.	•Immediacy of reinforcement is an important parameter to effective incentive interventions [35]. Delayed rewards are usually discounted, but are about twice as effective when delivered immediately [35].
Reset	•If the index participant tests positive for smoking or has a missed assessment, he/she will receive no reward for that check-in. The value of the next incentive earned for smoking abstinence will be reset to the value of the last reward attained, and the escalation scheme will start again at this value.	•Reset is a key parameter of effective incentive interventions to ensure rewards are contingent on smoking abstinence and to allow participants to continue their participation without loss of any rewards earned previously [36].
Regret aversion	•If the index participant is not abstinent, each dyad participant will get feedback via text message that they will not receive a reward at that time point but will be encouraged to continue their participation.	•Anticipated regret, is an important principle of behavioral economics; when facing a decision, individuals might anticipate regret from smoking, and thus choose to eliminate or reduce this possibility [36].
Text messages	•After each of the six smoking status assessments, study staff will deliver a standardized text message to each dyad participant on reward value earned for smoking abstinence and reinforce continued participation.	•Text messages will reduce delays in receiving information on rewards earned at smoking status check-ins.

Table note: CO = carbon monoxide, ST = smokeless tobacco including Iqmik (an Alaska homemade product), NRT = nicotine replacement therapy.