Table 2: Experimental activities timeline. Between sub- ject Practice round 1 Round 2 Round 3 Time prefer- ences task Round 4 Control group Effort task ex- plained and prac- tice round given. Effort task with no incentives; no incentives or fu- ture rounds men- tioned. Effort task with no incentives; no incentives or fu- ture rounds men- tioned. Effort task with no incentives; no incentives or fu- ture rounds men- tioned. Time preferences task explained and given; next effort task round not mentioned. Effort task with no incentives; no incentives mentioned nor that this is the last round. Extrinsic in- centive groups (four separate groups, each with a different type of incentive) Effort task ex- plained and prac- tice round given. Effort task with no incentives; no incentives or fu- ture rounds men- tioned. Effort task with extrinsic in- centive depending on treatment no future rounds mentioned. Effort task with no incentives; made clear that no incentives are given in this round, no future rounds mentioned. Time preferences task explained and given; next effort task round not mentioned. Effort task with no incentives; made clear that no incentives are given in this round, not men- tioned that this is the last round. Task time limit instructions) 2 minutes 5 minutes 5 minutes 5 minutes No time limit 5 minutes
Figure 1: Example screen of real effort task given to participants, with the code for the first letter of the “word” completed. without mention of incentives or future rounds of the task. However, participants in the extrinsic incentive treatment groups were given an incentive to complete each word in the task during this round. The incentive given depended on the between subject treatment group – see Section . Like the control group, the participants in the in- centive groups were not told about future rounds at this stage either. Therefore, round 2 gives a measure of the effect of the incentives, given baseline intrinsic motivation measured in the practice round and round 1. After round 2, participants proceeded to round 3, which was the real effort task for another 5 minutes. There were no incentives given in this round; participants in the incentive groups were told this explicitly, whereas those in the control group were again just given the task without mention of incentives. This round gives a measure of whether the incentives crowd in or crowd out intrinsic motivation, given baseline intrinsic motivation measured in the practice round and round 1. Next the participants were given a time preferences task, which is explained in more detail in Section . This task was given to participants at this point to give them a break from the real effort task to test whether the patterns measured in round 3 persisted after a break. Thus, after the time preferences task participants were given the effort task in round 4 for another 5 minutes, with the same treatment as round 3. That is, no incentives were given, which was explained to those in the incentive treatments but not mentioned to those in the control. It was not mentioned that this was the last round of the effort task.
Table 3: Between subject treatment groups. Treatment group Incentive applied (in Round 2 only) Control None Low power $0.05 paid per word High $1 paid per word High power threshold $23 paid if complete 23 words; $1 paid per word above this amount Charity 2 words plants one indigenous tree within Victoria (equiva- lent to $1 per word) participants received AUD$0.05 for each 5 letter “word” completed during the 5 minute time limit of round 2. The high power treatment group received AUD$1 per word in round 2. Those participants in the high power threshold treatment received AUD$23 if they completed 23 words; below 23 words they received nothing, but for each word completed above 23 they received AUD$1. Finally, participants in the charity treatment were told “every 2 words you complete will fund the planting of one indigenous tree in Victoria. A local environmental charity will receive the funds to plant these trees after the experiment.” The charity to which the funds were given, Tree Project, quotes on their website that every AUD$2 donated leads to one tree being planted. Thus, while participants were not told the monetary amount of their donation until the end of the experiment, it is equivalent to AUD$1 per word completed. The difference from the high power treatment is that donations were done in $2 increments. To ensure credibility of donations, participants were also told before round 2 started that a session-level donation receipt would be emailed to them to prove the donation had been made, which would include the average number of trees planted per person. Time preferences task The time preferences task consisted of 18 questions as shown in Table . The nine questions were repeated for today versus 5 weeks, and 5 weeks versus 10 weeks. This design means we can determine whether the participant is present or future bias, along with giving us a measure of how impatient the participants are. It was explained at the start of the task that one question would be randomly selected to be paid out. The payments for this task were made using a WISH gift card, which can be used at one of the common supermarket chains, a major department store chain and a range of other chain stores. The gift card was chosen as it can be used at a large number of stores where people commonly shop, and can be sent via the post. It does not have the transaction costs of going to a bank to deposit a cheque. 2 accessed 23 August, 2016.
Table 15: Difference in difference model for rounds 1 to 3, with NEP interaction terms included. Dependent variable: Rounds 1 to 3, words/minute Constant (1.091) 2 dummy (0.476) Round 3 dummy 0.511 (0.642) Low power 0.413 (1.318) High power 0.700 (1.445) High power thresh −1.725 (1.428) Charity 0.569 (1.422) Low power*R2 −0.553 (0.611) High power*R2 (0.629) High thresh*R2 −0.621 (0.649) Charity*R2 (0.685) Low power*R3 −0.212 (0.759) High power*R3 −1.047 (0.957) High power thresh*R3 0.143 (0.726) Charity*R3 −0.792 (0.863) NEP 0.013 (0.286) NEP*R2 −0.187 (0.128) NEP*R3 −0.026 (0.167) Low p*NEP −0.111 (0.352) High p*NEP −0.081 (0.376) High p thresh*NEP 0.489 (0.380) Charity*NEP −0.108 (0.387) Low p*NEP*R2 0.184 (0.163) High p*NEP*R2 (0.166) High p thresh*NEP*R2 0.166 (0.168) Charity*NEP*R2 (0.191) Low p*NEP*R3 0.033 (0.198) High p*NEP*R3 0.169 (0.240) High p thresh*NEP*R3 −0.082 (0.190) Charity*NEP*R3 0.208 (0.235) Notes: Standard errors clustered at the individual level are in parentheses. Level of exercise dummies are relative to high exercise.