We considered a stress test of experimenter demand effects.
Altruism towards the experimenter is unable to explain the key finding of destruction of coupons by roughly one subject out of three, the same as the fraction of subjects who returned money to the experimenter.
While the latter can be explained by altruism, the former cannot ; the strong positive correlation between coupons destroyed and money returned to the experimenter is also left unexplained by an explanation based on altruism towards the experimenter.
Confusion is unlikely to be behind this as the tasks were simple, subjects' understanding was checked, and variables for clarity of the instructions on the destruction task were either statistically non significant or positively rather than negatively correlated with destruction. Subjects valued the coupons (see footnote 9) and our analysis also controlled for the pleasure of physical destruction by ensuring that the same physical destruction activity took place regardless of how many coupons were destroyed; and for the possibility of benefiting the café coupon providers by having a relevant question that went into our regression analysis.