Disentangling the Sources of Pro-social Behavior in the Workplace: A Field Experiment

To summarize, the distribution of productivity changes displays a significant shift to the right
for both treatments compared to the control group, while there is no difference between treatments.
This implies that action-oriented altruism is motivating subjects to work harder, while there is no
evidence of output-oriented altruism. Looking at the data disaggregated by gender, we find that
the effect is very strong for women, while it is insignificant for men. We now proceed to quantify
the strength of this motivation, both non-parametrically and through regression analysis. One way
to estimate the shift in the distributions between the two treatments and the control group non-
parametrically is to use the Hodges-Lehmann median difference. For females, this equals 0.104,
implying a 10.4% additional increase in productivity compared to the control group due to action-
oriented altruism, and is significant at the 5% level.

Table 2 - Statistical Test Results

All   Men  Women

Control vs Treatment A

Mann-Whitney test    0.066  0.379   0.028

Kolmogorov-Smirnov  0.044  0.349   0.030

Control vs Treatment B

Mann-Whitney test    0.084  0.418   0.041

Kolmogorov-Smirnov  0.115  0.679   0.040

Treatment A vs Treatment B

Mann-Whitney test   0.482  0.478   0.413

Kolmogorov-Smirnov  0.429  0.380   0.438

One-tailed p-values are reported.

The magnitude of this effect is in line with the one obtained in a regression setting. Due to
the presence of several outliers (see the box-whiskers graphs, Figure 4), we use a quantile (median)
regression approach. The following equation is estimated

^yi — ^βo % ^βi^DAi + β%DOi + ɛj,

where y⅛ is the percentage change in productivity between the first and the second sessions for
subject г, DO is a dummy equal to 1 if the subject is in treatment B, while DA is a dummy equal
to 1 if the subject has been treated. Thus, β₂ measures the increase in productivity due to output
oriented altruism, while β ₁ measures the increase in productivity due to action-oriented altruism.
Consistently with the non-parametric tests, for the whole sample the coefficient of the dummy

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