Download npeNPE20131060instructions3nopictures1

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.