Implementation Details ---------------------- **UPDATE (posted 4/26)** This update is to document a change in the show-up fees that went into effect on March 2nd, 2016. The original pre-registration plan was to recruit subjects at a show-up fee of \\$5. However, show-up rates were very slow and several sessions had to be cancelled in February 2016 because fewer than 12 participants had shown up for the session. While the exact cause for the slow show-up rate is unclear, the university's lab manager believes that it is because researchers using the same subject pool at Harvard have started paying above-market show-up wages to attract more subjects, which has led participants to expect higher payments overall. In response to this circumstance, and after consulting with RRR Editor Daniel Simons on February 25th, I decided to raise the show-up fee from \\$5 to \\$8. The increased show-up fees took effect in March 2016 and continued for all remaining sessions throughout March and April 2016. Specifically, the last session to be conducted with a \\$5 show-up fee was on February 23rd; the first session with a \\$8 show-up fee took place on March 2nd. The increase in show-up fees worked as expected: the \\$8-show-up-fee sessions were well attended and data collection could be completed successfully. **ORIGINAL PROTOCOL FROM HEREON** This page describes how our lab implemented the procedures required by the official protocol for the RRR. It also describes and justifies any additions to or departures from that protocol. You can view the official protocol and the main project page for this RRR using these links: - Official Protocol: [https://osf.io/ypd78/][1] - Main RRR project page: [https://osf.io/scu2f/][2] ---------- #### Experimenters #### Oliver Hauser is a fourth-year doctoral student at the Program for Evolutionary Dynamics at Harvard University. His research lies at the intersection of behavioural economics and evolutionary game theory. He has gained much experience running experiments, both online and in the physical laboratory (Harvard Decision Science Lab [HDSL]). The replication experiment will be carried out by Hauser and HDSL research assistants. The research assistants will be trained on the protocol by Hauser. The research assistants will help with seating participants, reading instructions out loud, and bringing payment to them at the end of the study. **Note**: Two of the original authors (David Rand and Martin Nowak) of Rand et al. *Nature* (2012) are, or at some point were, affiliated with the Program for Evolutionary Dynamics at Harvard, at which the author of this replication study (Oliver Hauser) is currently working. Nowak is the faculty director of the program and Hauser's doctoral advisor. Neither Nowak nor Rand are, however, advising Hauser on this replication project. Rand brought the APS call of this RRR to Hauser's attention, with the intention of having one of the replication studies being conducted at the original study site and with the original subject pool. (Rand was encouraged to contact labs with expertise in this topic area by the editor.) ---------- #### Setting/Lab/Equipment #### The Harvard Decision Science Lab (HDSL) is part of the Harvard Kennedy School of Government, located on the Cambridge campus of Harvard University. Participants enter the HDSL waiting room and will be checked in and seated by a research assistant. Each participant is seated at a cubicle that contains a computer, mouse and keyboard. Privacy is ensured through separating walls between the cubicles. In total, HDSL provides room for up to 36 participants in a given session. More information about the lab equipment can be found on their website at [http://decisionlab.harvard.edu/about/capabilities][3] ---------- #### Sample, subjects, and randomization #### **Target sample size:** I will aim to recruit at least 160 participants in total (80 per condition). To achieve this target sample size, I plan to conduct 5 sessions with up to 36 participants each. Depending on sign-ups and show-ups on any given day, the total number of participants might be as high as 180 participants if the lab is full in all sessions, or it could be less if fewer participants show up. **Target sample demographics:** I will recruit participants using HDSL's internal recruitment system (SONA). I will keep with the protocol requirements for recruitment: ≤ 35 years, between 20-80% female, and naïve subjects. (In the past, this recruitment has also led to representative show-ups.) Compensation will be twofold: first, participants will receive a show-up fee of $5 for participating. Second, they can earn more money depending on their and others' decisions. **Minimum sample size after exclusions:** The minimum sample size for this study will be 80 participants in each condition. **Stopping rule(s):** I will schedule 5 sessions of 36 participants (160 total). If due to no-shows or exclusions, there are fewer than 80 participants in either condition, I will schedule additional sessions of 36 participants until there is a minimum of 80 usable participants in each condition. **Randomization to conditions:** Participants will be randomly assigned to conditions by the provided Qualtrics Script. **Blinding to conditions:** Participants will read the instructions on their computers, which provide privacy through cubicle separation walls. Participants will not be allowed to speak to one another. Thus there should be minimal risk of contamination between conditions. **Exclusion rules:** I will use the same exclusion rules as outlined in the official protocol. **Procedures for handling testing sessions for which the number of participants is not a multiple of 4:** As participants arrive at the HDSL waiting room, they are being checked in by a research assistant. Participants will then be seated by the research assistants one at a time. Participants will only be seated when at least 12 participants are in the waiting room and each time when approximately 6-8 participants are available for seating thereafter. (I will avoid seating people in groups of exactly 4 at a time in order to minimise the probability that participants (erroneously) believe the seated people are also their group members.) Any remaining (not multiple of 4) participants will not be able to participate in this study and will not be seated. In accordance with HDSL procedures, they will be paid the show-up fee for arriving on time and invited to sign up for another study or another session of the same study if they wish. (Since they have not been seated, they will not have read any instructions or learned anything about the experiment at this point.) ---------- #### Software/Code #### I will use the officially provided materials. They will be verified at HDSL after IRB permission has been secured but before recruitment begins. ---------- #### Differences from the official protocol #### No differences or additions are planned. [1]: https://osf.io/ypd78/ [2]: https://osf.io/scu2f/ [3]: http://decisionlab.harvard.edu/about/capabilities