Methods and materials

 
ellsberg paradox
 

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The Department of Environmental Economics and Management

The Robert H. Smith Faculty
of Agriculture, Food and Environment
The Hebrew University of Jerusalem

PO Box 12, Rehovot 76100
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Department Head:
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Choice Prediction Competition for Decisions under Risk and Ambiguity

CPC 2015 - Supported by the Max Wertheimer Minerva Center
for Cognitive Processing and Human Performance

Organized by: Ido Erev, Eyal Ert, and Ori Plonsky

In each session each participant faced 30 decision problems for 25 trials. The order of the 30 problems was random. 
Participants were told that they were going to play several games, each of which for several trials, and their task in each trial is to choose one of the two options on the screen for real money. The instructions also stated that at the end of the study one of the trials would be randomly selected, and that the participantsb obtained outcome in that trial would be realized as their payoff. In the first five trials of each problem, the participants did not receive feedback after each choice; thus they had to rely on the description of the payoff distributions. Full feedback (the outcome of each of the two prospects) was provided after each choice starting at Trial 6; that is, in the last 19 trials the participants could rely on the description of the payoff distributions and on feedback concerning the outcomes of previous trials. 
The choice problems were run in two order conditions: In the "By Problem" (ByProb) condition they faced each problem for one sequence of 25 trials. The bBy Feedbackb (ByFB) condition was almost identical to the ByProb condition with one exception: The participants first performed the five no-feedback trials in each of the 30 problems (in one sequence of 150 trials), and then faced the remaining 20 trials with feedback of each problem (in one sequence of 600 trials, and in the same order of problems they have played in the no-feedback trials). 
The final payoff (including show-up fee) ranged between 10 and 144 Shekels (M = 45.2)

The instructions to participants in the ByProb condition: 
bThis experiment consists of many games which you will play one after the other. 
In every game there are multiple trials and in every trial you will have to choose between two options presented on the screen. The choice will be made by clicking on the button that corresponds with the option you have selected, which will be located below that option. 
Following some of the trials there will appear on the selected button the outcome you obtained by selecting that option (this outcome will appear in black font). On the other button there will appear the outcome you could have obtained had you selected the other option (the forgone outcome will appear in dull font). 
In the end of the experiment one trial will be selected at random from all the experimentbs trials and your obtained outcome in that trial will be your payoff for the performance in the experiment. Trials in which outcomes did not appear on the screen may also be selected to count as your payoff. 
Please note: The more trials you have with larger obtained outcomes, the larger the chances you would get a larger monetary pay in the end of the experiment.b

The instructions to participants in the ByFB condition: 
bThis experiment consists of many games which you will play one after the other. 
In every game there are multiple trials and in every trial you will have to choose between two options presented on the screen. The choice will be made by clicking on the button that corresponds with the option you have selected, which will be located below that option.
In the end of the experiment one trial will be selected at random from all the experimentbs trials and your obtained outcome in that trial will be your payoff for the performance in the experiment. Please note: The more trials you have with larger obtained outcomes, the larger the chances you would get a larger monetary pay in the end of the experiment.b 
After completing all (150) No-FB trials (five per problem), the participants in the ByFB condition were shown the following instructions: 
bThe first part of the experiment is over. In the second part of the experiment, there will appear on the selected button the outcome you obtained by selecting that option (this outcome will appear in black font). On the other button there will appear the outcome you could have obtained had you selected the other option (the forgone outcome will appear in dull font). 
The rest of the instructions remain unchanged.b

Screenshot examples of the experimental paradigm are given in Figures B1 through B5: Figure B1 demonstrates a problem with abstract representation and Amb = 0; Figure B2 demonstrates a problem with abstract representation and Amb = 1; Figure B3 demonstrates the coin-toss framing manipulation; Figure B4 demonstrates the accept/reject framing manipulation; and Figure B5 demonstrates the feedback given to participants following a choice. Note the location of each option on the screen was counterbalanced and the information regarding correlation between options (bottom row on the screen) only appeared if both options had more than one possible outcome (i.e. when correlation information was relevant).