Elicited bid functions in (a)symmetric first-price auctions

Subjects could participate in only one session. At the outset of each session, they received
instructions that were read aloud (a translation of the instructions is reported in Appendix 1)
and they were provided a demonstration of the software, using values drawn from different
distributions than those used in the experiments.⁸

Subjects were then randomly assigned to computer terminals. They were informed that they
would keep their respective types for the whole experiment. In each group of subjects, three
subjects were of the Strong type and three subjects were of Weak type. Each subject
interacted only with the three subjects of the other type that were in her/his group. Although
bidders in the SYM treatment are all of the same type, we used the same matching procedure
as in the asymmetric treatments so as to keep the statistical analysis of subjects’ behavior in
terms of types comparable across treatments.

All subjects participated in 100 auction rounds. At the end of each auction, each participant
was informed on the own value, the own bid (that resulted from applying the chosen bid
function to the value), the winning bid, and the own payoff (0, if they lost the auction; [value
- bid], if they won). This information (including the complete own bid function) was
appended to a “History” window that could be retrieved at any time during the experiment.

3. Results

Most of our conclusions are based on the outcomes of randomization tests for independent or
related samples of independent observations (Siegel and Castellan, 1988). When we state that
we have found no significant effect, we mean that the test result was not significant, even at
α = .10, one-tailed. Furthermore, we recall that after each round, subjects are randomly re-

⁸ A screenshot of the software (based on RatImage by Abbink and Sadrieh, 1995) is included in the appendix.

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