In our online Amazon Mechanical Turk (MTurk) experiment, a total of 1,600 participants made
incentivized choices as “rich” players, in groups with an equal number of rich and poor players. The
“rich” were endowed with 350 cents and the “poor” were endowed with 10 cents. We varied two key
dimensions of the decision-making environment.
First, half of our participants were part of small groups of 4 people, whereas the other half were
in groups of 200 participants. This was varied between participants.
Second, we introduced within-subject variation in the types of giving decisions. The first type
involved an option for individual giving, with the gift distributed equally among all of the poor
participants. The second type involved an individual giving decision where the gift would be assigned
to one randomly chosen poor participant, but in such a way that no poor participant received a gift
from more than one rich participant. We call both of these first two types of decisions “individual
giving” because a participant’s decision to give does not affect transfers from other rich participants.
This is in contrast to our third type of decision, where the rich participants voted on whether a
transfer should be made from all rich participants to all poor participants.
Additionally, we varied the cost of transfers to the poor within-subject, so that each participant
took part in a total of 9 decisions: 3 decision types × 3 different costs of giving. Finally, we varied
the framing of individual giving to one participant. In one frame we described the recipient as a
“matched partner” while in another frame we described the recipient as a “randomly selected person.”
This manipulation was conducted to test the malleability of perceived group size; in particular to
test whether participants who initially started out in larger groups might perceive themselves to be
in a small group of 2 when the recipient is described as a “matched partner,” and thus would more
willing to give.