Investments in the different options in games with and without a group resource.

aParticipants invested significantly lower absolute amounts in keeping, taking and defense in CKTD than in KTD (all Fs >24; all ps <0.001).
bThere was no significant difference in the relative amounts invested in each of the three options in CKTD versus KTD (all Fs <2; all ps >0.2).
cParticipants invested significantly more in taking money than in either defense or keeping money (F(1,17) = 5.21, p = 0.017) in the KTD condition. In the CKTD condition, the results were in the same direction but were not significant (relative amounts: F(1,17)  = 3.15, p = 0.069; absolute amounts: F(1,17)  = 2.60, p = 0.103).
dTotals may not sum exactly to 100 due to rounding.
Mean (± s.e.) investments in lab dollars in the experimental conditions with and without the option to contribute to a public good (CKTD and KTD respectively). Participants could spread their money among four options in the CKTD condition, compared to three in the KTD condition; in order to control for this, the “relative amount” column shows the amounts participants kept and invested in taking and defense relative to the sum of investments in these three options.