PERSonalised Incentives for Supporting Tobacco cessation (PERSIST) among healthcare employees: a randomised controlled trial protocol 345 10 and 4. Willingness to pay a deposit, yes or no The first three factors have been associated with the effectiveness of smoking cessation interventions and with reaching sustained abstinence in rewardbased programs.14 The fourth factor is used as an indicator of acceptability of the deposit-based scheme, as deposit schemes are expected to be the most effective but also the least popular. The four factors are dichotomised into “positive” or “negative” values in order to advise participants. Positive values are associated with higher quit percentages, i.e. being in a preparation stage, being low tobacco dependent and having a delayed reward preference. Negative values are associated with lower quit percentages, i.e. being in a (pre-)contemplation stage, being dependent on tobacco and having an immediate reward preference. A combination of three positive values leads to the ascending scheme, two positive values to the standard scheme and two or three negative values to the descending scheme (see table 1). Those willing to pay a deposit are automatically advised the deposit-based scheme. The rationale behind this is that those with the lowest scores are likely to experience the most trouble quitting, and hence arguably benefit most from higher rewards in the beginning. Those with a higher score might rather benefit from incentives as a motivator to remain abstinent, and thus receive higher rewards towards the end of the study period. Importantly, participants are however free to choose the scheme of their preference when entering the trial regardless of the advice they received. As participants have freedom of choice over the incentive schemes, this is likely to result in a skewed distribution of participants over the schemes. However, this is not an issue in the current trial as the aim is to estimate the effect of personalised incentives compared to no incentives and not to estimate the discrete effects of the individual schemes. In fact, the current trial will provide information as to which schemes are most popular, how this relates to personal characteristics, and whether participants may be nudged into the scheme that is assumed to best fit their personal characteristics.
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