Fig. 3: Study 2b, monetary vs pooled non-monetary conditions in the United States and Mexico.

Effects of a monetary incentive (green) and pooled non-monetary treatments (flat fee and social norm; blue) in Mexico (N = 1,053 participants recruited on Prolific) and two samples in the United States: one with the same nominal pay (N = 1,098 on Prolific) as in Mexico and one with the same subjective¹⁰⁷ pay (N = 1,122 participants recruited on Prolific) as in Mexico. a, The central tendency and distribution of effort by incentive type and country. The black line within each box represents the median and the red dot shows the mean; upper and lower bounds show the third and first quartiles, respectively; whiskers represent 1.5× the interquartile range, with black dots showing observations outside of this range. The width of each violin corresponds to the frequency of observations at any given number of images rated on the y axis. The interaction between country and incentive type in a multiple linear regression model is statistically significant (b = 13.93, t(2,143) = 3.42, P < 0.001, 95% CI 5.94–21.92 for the comparison between Mexico and the US sample with the same nominal pay; b = 19.28, t(2,167) = 4.71, P < 0.001, 95% CI 11.26–27.30 for the comparison between Mexico and the US sample with the same subjective pay). b, The money advantage, that is, how much more effective money is than the pooled non-monetary treatments in each sample. In b, error bars are bootstrapped 95% CIs for the mean relative difference in the number of images rated in the monetary vs pooled non-monetary conditions.