Randomization Method
Participants are asked to come to the lab in groups. To run a study ‘session’ there must be at least n=6 participants. Ideally, there will be n=9 or n=12 participants at a time.
Allocation to groups is random, using a blocked design. The study managers (either Ben Weidmann or Research Assistants at the HDSL) will apply the following principles:
- Avoid allocations where people are in a group with the same person more than once. In cases where n=6, this will not be possible, but will be adjusted for the analysis.
- Avoid where people are working with people they know
- Attempt to balance groups so that the overall level (and variance) of skill in each group is as-similar-as-possible across groups
To achieve these aims, we apply the following procedures
- The n participants in each session are divided into three equal blocks of size n/3, based on their overall score in Battery A [if n is not a multiple of three, excess participants are paid for their time and asked to return to another session]. Blocks can loosely be thought of as ‘high’, ‘medium’, and ‘low’ in terms of individual skill.
- If people arrive at the lab with friends, they are automatically placed in the same block.
- There are three bags, one for each block. Each bag has n/3 balls, marked with a letter. Bags have consecutive letters. For example, in a session of 9 people, the bag for ‘high’ performance will have balls with A,B,C; the ‘medium’ bag will have D,E,F; and the final bag has G,H,I.
- Each participant draws a ball. This ball defines their 2 groups for that session. To return to the example of a 9-person session, allocations would be as follows: first set of groups: {ADG,BEH,CFI}; second set of groups: {AEI,BFG,CDH}.