Four examples of financial incentives in euros according to abstinence (A)/non-abstinence (Ā) of pregnant women at study visits (V)
| Scenario for 5 visits | R=V1 (€) | V2 | V3 | V4 | V5 | Total gain |
|---|---|---|---|---|---|---|
| 1. RAAAA | 20 | A  | A  | A  | A  | 20+360 |
| 2. RAAĀĀ | 20 | A  | A  | Ā  | Ā  | 20+180 |
| 3. RAĀAĀ | 20 | A  | Ā  | A  | Ā  | 20+160 |
| 4. RĀAAĀ | 20 | Ā  | A  | A  | Ā  | 20+180 |
The first scenario RAAA refers to a participant who was randomised to the intervention group (IG) during the first visit and was abstinent in the following four visits. Hence, during the second visit (t=2), she would get a €20 voucher for showing up plus a €40 voucher for being abstinent (because she is abstinent
and because it's the first time since randomisation she's being checked for being abstinent, then ). At the last visit (t=5), showing up and being abstinent for the fourth time () yields a voucher of 20+20(4+1)1=€120.The second scenario RAAĀĀ refers to a participant who was randomised to the IG during the first visit and abstinent at the 2nd and 3rd visits, and non-abstinent at the 4th and 5th visits. Hence, for the second visit, the abstinent participant would receive the €20 voucher show-up fee plus the €40 voucher for being abstinent (
and ). At the third visit, by showing up she would get the €20 voucher, and by being abstinent () for the second consecutive time (), she would receive an additional €20(2+1)1 = €60 voucher, etc.If one looks at scenario 4, the participant is being randomised to the IG at the first visit, then is not abstinent at the 2nd visit, abstinent at the 3rd and 4th visits, and not abstinent at the 5th visit. Hence, during visit 4, for example, she would receive the €20 voucher for showing up, and, by being abstinent (
) for the second consecutive time (), she would get a €20×(2+1)×1=€60 voucher. However, as in the 5th visit she is not abstinent, she then gets the €20 show-up voucher.R, randomisation visit, V1.
