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Centre for Experimental Social Sciences EXPERIMENT March 2010 INSTRUCTIONS Please wait for the experimenter to indicate the start of the experiment. These instructions will be read aloud by the experimenter shortly. Dear participants, Welcome and thank you for participating to this experiment. Before we describe the experiment, we wish to inform you of a number of rules and practical details. Important rules Your participation is considered voluntary and you are free to leave the room at any point if you wish to do so. In that case, we will only pay you the show-up fee of £4. No writing: You are not allowed to use a pen or take notes during this experiment Silence: Please do remain quiet from now on until the end of the experiment. Those who do not respect the silence requirement will be asked to leave the experimental room. You will have the opportunity to ask questions in a few minutes. Finally, note that the CESS lab prohibits deception of subjects – thus you can be assured that all the information you will receive during the course of this experiment is true. What will happen at the end of the experiment Once the experiment is finished, please remain seated. We will need around 10 minutes to prepare your payment. We will move to another room and you will be called up successively by the number on your table; you will then receive an envelope with your earnings and you will be asked to sign a receipt. Description of the experiment The experiment consists of a short memory task. Your performance in the task will be important in determining your earnings. Each of you (each computer in front of you) has been assigned a set of 24 pictures. Each picture is associated with a “value” (a number between 10 and 70, see illustration below), value that will be important in determining your earnings. The experiment is structured in three stages. The first stage is a viewing stage – you will see the sequence of 24 pictures, together with the associated value. The second stage is a selection stage – you will see the same pictures again, but without their associated value, and will be asked to select 8 pictures among these 24, pictures that will enter a lottery. The third and last stage is a lottery, whereby one of the 8 pictures selected in stage 2 will be picked at random by the computer and your payment will be equal to the value corresponding to the picture, divided by 10 (e.g. if the selected picture has a value of 50, you will earn £5). We will explain each stage successively in more detail. STAGE 1: VIEWING In the first stage, you will see an automated sequence of the 24 pictures, together with their values. Each picture will be shown for 3 seconds and then the screen will move automatically to the next picture. At the end of the sequence, you will automatically come back to a screen that will enable you to proceed to stage 2. This is an example of what you could see on your screen: 52 Picture not shown for copyrights reasons STAGE 2: SELECTION STAGE The second stage will last for 3 minutes (180 seconds): you will see the pictures of the same 24 people again, but without their value and in a different sequence. You can use these 3 minutes to select up to 8 pictures in total. The selected pictures will enter a lottery that will determine your final earnings (stage 3, described further in the instructions). To select a picture, simply tick the box below the picture. The display of the pictures is not automated at this stage. You can go back and forth freely between pictures by using the mouse and clicking on the arrows at the bottom of your screen. Ticks can be removed and added until the end of the 3 minutes. However, you will not be able to select more than 8 pictures. You can unselect pictures by clicking again on the box you have previously ticked. If you wish to exit stage 2 before the end time; you can validate your selected pictures by pressing the button on the bottom right. This will end stage 2, so press this button only if you are sure you want to submit your choices. Alternatively, the computer will automatically stop stage 2 when the time is over (after 180 seconds). EXAMPLE OF A SCREEN VIEW IN STAGE 2 Picture not shown for copyrights reasons Box to tick Select or unselect this person Previous Go to the first picture Indicates number of pictures already selected Next Go to the last picture Press this when you have made selected all pictures of your choice (this will end stage 2) Important notes The pictures in stage 2 will be shown - without the associated value in a different sequence than in stage 1 will be from a different angle than in stage 1 – See the illustration below. Example of two different picture angles for the same person: STAGE 1 Picture not shown for copyrights reasons STAGE 2 Picture not shown for copyrights reasons If you have selected less than 8 pictures by the end of the 3 minutes, the computer will automatically add pictures to complete the selection. The computer will select pictures at random among the remaining pictures (that is, among those you have not selected) and add as many as necessary to obtain a set of 8 pictures. Thus, there will always be 8 pictures recorded in the computer at the end of stage 2. STAGE 3: LOTTERY The third stage is a lottery: The computer will choose at random one of the pictures among the set of 8 pictures selected in stage 2. Each picture is equally likely to be selected. Think of a deck of 8 cards, each card corresponding to a picture selected in stage 2, and one of these 8 cards is drawn at random. This is illustrated in the drawing below. IMPORTANT: The value of the picture drawn by the computer lottery will determine your final earnings! Your earnings will be equal to the value of the picture drawn in the lottery divided by 10. Examples Example 1 – Complete selection by yourself in stage 2 - Suppose you selected 8 pictures yourself in stage 2 and the values corresponding to these pictures in stage 1 are 50, 65, 68, 12, 45, 56, 39 and 28. Your payment will be equal to one of these 8 values; for example if the picture picked by the computer lottery has a value of 45, then your payment will be equal to £4.5 Example 2 – Incomplete selection - Suppose that you only selected 6 pictures in stage 2, which have the following corresponding values: 50, 65, 68, 12, 45, 56. Then the computer would pick 2 additional pictures at random among the remaining non-selected pictures, pictures that could for example have the following values: 37 and 52. Then the computer will select one of these 8 pictures to determine your payment. For example, if the picture picked is 52, then your payment will be equal to £5.2 You can see from both examples that your earnings crucially depend on the values of the 8 pictures selected in stage 2. A selection of pictures with high values is more likely to translate into high earnings than a selection of pictures with low values. What you will see on your screen You will see a screen summarising the selection of pictures that entered the lottery: one column indicates the pictures you selected and the other column indicates the pictures selected by the computer. Your final score (the outcome of the lottery) will be indicated on top of the screen. You can scroll down the screen to see all pictures. Please leave this window open (to ensure we know your score). EXAMPLE OF SCREEN IN STAGE 3 The values It is useful to know how the values of the pictures have been determined. These values are numbers between 10 and 70 that have been pre-assigned by the computer. To understand how these values have been pre-assigned, it is easiest to imagine that each value has been determined by the outcome of a roulette game as the one shown below. You can see that the roulette is not a standard roulette; the value can be any round number between 10 and 70, but all numbers are not equally likely to be drawn. Numbers closer to 40 (the mean) are more likely to be drawn than numbers further away from 40. In fact, the ball has 70% chances of falling on a value between 25 and 55. Thus, you are more likely to see values close to 40 than values close to 10 or 70. The roulette has been played for each picture separately; the computer recorded the number drawn and assigned it to the picture. Thus, the roulette was played 24 times (see the illustration on the next page). This is how the values have been assigned. Note: The description above is sufficient to understand the experiment, but those who are familiar with statistics may find it useful to know that the value corresponds to a random draw from a discrete normal distribution (truncated at 10 and 70), with mean equal to 40 and standard deviation 15. ILLUSTRATION: Pre-assignment of values to pictures by the computer Intermediary stage Note that between stage 2 (selection stage) and stage 3 (lottery and results), you will be asked to fill in a small questionnaire asking for some background information. This questionnaire has no implications for your earnings but is useful for our study. The information will be kept confidential and anonymous. We would be grateful if you can fill it in carefully. End of the experiment Once you have finished the experiment, please remain seated and wait for the experimenter to indicate the end of the experiment. Once everyone in the room has finished, you will be allowed to leave the experimental room and go to the waiting room for your payment. Please do take with you the number you have been assigned to. Summary Stage 1: Viewing stage: 24 pictures for 3 seconds each (automated sequence) Stage 2: Selection stage: You select up to 8 pictures among the 24 (go back and forth between pictures for 3 minutes) – computer completes the selection if necessary Participant information (Questionnaire) Stage 3: Lottery and results The computer picks at random (lottery) 1 of the 8 pictures selected in stage 2. The value attached to the picture determines your earnings. The exchange rate is 10 points = £1 Thus, your final earnings = £4 (show-up fee) + earnings of stage 3 If you have any questions, please raise your hand now and wait for the experimenter to come to you. Please leave these instructions on your table when you leave the room.