We run six treatments: HOM, HET, BEL-MULTI, BEL-FULL, SPEC-FULL and PRIV.
In HOM and HET we run markets identical to FULL where matching in groups is determined by IDM evaluations. In HOM we will form homogeneous groups including the 50% of the subject population that is closest to the median evaluation. In HET we will form heterogeneous groups, including the 50% of subjects that are most distant from the median.
We further run two market treatments, BEL-MULTI and BEL-FULL, which are identical in all aspect to, respectively, MULTI and FULL, except for the introduction of a belief elicitation task during trading, where subjects report their belief that trade will continue for the next unit as well as the number of active traders they expect there to be. Here, before the trade of unit 10, 12, 13 and 15, subject reports beliefs about: (1) how many other traders (other than themselves) will be active in the trading of the next unit; (2) the probabilities that: (i) their choice to trade is consequential for trade to happen; (ii) trade stops irrespective of what they do; (iii) trade continues irrespective of what they do.
In SPEC-FULL, subjects will only act as observers of the market and report beliefs. That is, each subject in SPEC-FULL is linked to a subject of a previous BEL-FULL matching group. The "observer" subject monitors how play unfolded in the linked matching group. At identical moments as in BEL-FULL, the "observer" subject reports beliefs about: (1) how many other traders (other than the linked trader) will be active in the trading of the next unit; (2) the probabilities that: (i) the linked trader's choice to trade is consequential for trade to happen; (ii) trade stops irrespective of what the linked trader does; (iii) trade continues irrespective of what the linked trader does.
In PRIV, we run a market treatment with private demand and supply schedules which are assigned such that aggregate demand and supply are equal to the MULTI/FULL market setup.
Because the subject pool of the University of Amsterdam is not large enough to run all treatments, we will run approximately 65% of the sessions of each treatment (excluding PRIV) at Tilburg University. The exception will be for PRIV, that we intend to compare to the previous treatments FULL and MULTI. Given that the previous treatments were all run at the University of Amsterdam, we will do the same for PRIV.
For completeness, we report below the experimental design details from Ziegler et al. (2021) that remain common features of the treatments in the present study.
All markets consist of 10 participants, 5 per market side (buyers/sellers). In BEL-MULTI and PRIV each participant can trade up to 3 units; in HOM, HET, and BEL-FULL, each participant can trade up to 15 units. Across all markets (excluding PRIV), there is a common supply/demand schedule, which means that costs/values for trading a unit only depend on the aggregate number of units traded previously. In all treatments (except SPEC-FULL) participants first participate in the elicitation of their valuation of charity donations. Afterwards, they participate in the markets; lastly, they face the identical individual elicitation as before the start of the market.
Across all treatments (except SPEC-FULL) , the experiment will conclude with elicitations of: i) the median of the distribution of valuations of charity donations; ii) social norm elicitation about behavior in markets and in individual decision-making; iii) risk preferences.