oTree: Individual decision making

Forms

Submitting information

• Each page in oTree can contain a form
  • The player fills with some value and then submits it
    • Cardinal values
      • Integer, Float
    • Ordinal values
      • Integer, Categorical
    • Text
      • Strings of numbers and letters
• Several formats to collect values
  • Open fiels
  • Buttons
  • Radio buttons
  • Dropdown lists
  • …

Basic structure of forms

• First create fields in models.py
• As an example, if you want to collect name and age

class Player(BasePlayer):
    name = models.StringField(label="Your name:")
    age = models.IntegerField(label="Your age:")

• Then in pages.py, you will create a class

class Anag(Page):
    form_model = 'player'
    form_fields = ['name', 'age'] # saved as player.name, player.age

• Finally, in the template Anag.html the form will be displayed with

{% formfields %}

• To display the forms separately

{% formfields player.age %}

Input formats

Examples

• In the following examples the participant receives a random number
• The participant is asked to report features of the number
  • Several input interfaces are presented
    • Radio
    • Button
    • Checker
    • Dropdown
    • Radio Sequence
    • Text
    • Value
    • Tabular

Radio

• Models

input_radio = models.CharField(
    choices=['Odd', 'Even'],
    widget=widgets.RadioSelect)

• Pages

class Radio(Page):
    form_model = 'player'
    form_fields = ['input_radio']

• Template

{% block content %}

{% formfield player.input_radio label="The number is:"%}

  {% next_button %}

{% endblock %}

Button

• Models

class Player(BasePlayer):
    input_button = models.CharField()

• Pages

class Button(Page):
    form_model = 'player'
    form_fields = ['input_button']

• Template

  • This widget does not rely on oTree functionalities
  • Raw HTML with bootstrap features

{% block content %}

The number is:
<button name="input_button" value="Even" class="btn btn-outline-primary" btn-lg">Even</button>
<button name="input_button" value="Odd" class="btn btn-outline-primary" btn-lg">Odd</button>

{% endblock %}

Checker

• Models

class Player(BasePlayer):
  input_checker = models.CharField(
    choices=[
            ["Even", 'Yes'],
            ["Odd", 'No']
            ],
    widget=widgets.RadioSelectHorizontal,
    label="Is the number even?")

• Pages

class Checker(Page):
    form_model = 'player'
    form_fields = ['input_checker']

• Template

{% block content %}

{% formfield player.input_checker %}

    {% next_button %}

{% endblock %}

Dropdown

• Models

class Player(BasePlayer):
    input_dropdown = models.IntegerField(
    choices=[1, 2, 3, 4, 5, 6, 7, 8, 9])

• Pages

class Dropdown(Page):
    form_model = 'player'
    form_fields = ['input_dropdown']

• Template

{% block content %}

{% formfield player.input_dropdown label="The number is:"%}

    {% next_button %}

{% endblock %}

Radiosequence

• Models

class Player(BasePlayer):
    input_radiosequence = models.IntegerField(
        choices=[1, 2, 3, 4, 5, 6, 7, 8, 9],
        widget=widgets.RadioSelectHorizontal
        )

• Pages

class RadioSequence(Page):
    form_model = 'player'
    form_fields = ['input_radiosequence']

• Template

{% block content %}

{% formfield player.input_radiosequence label="The number is:"%}

    {% next_button %}

{% endblock %}

Text

• Models

class Player(BasePlayer):
    input_text = models.CharField()

• Pages

class Text(Page):
    form_model = 'player'
    form_fields = ['input_text']

• Template

{% block content %}

{% formfield player.input_text label="The number is:"%}

    {% next_button %}

{% endblock %}

Value

• Models

class Player(BasePlayer):
    input_value = models.IntegerField(min=1, max=9)

• Pages

class Value(Page):
    form_model = 'player'
    form_fields = ['input_value']

• Template

{% block content %}

{% formfield player.input_value label="The number is:"%}

    {% next_button %}

{% endblock %}

Tabular (i)

• Models

class Player(BasePlayer):
    tab_1 = models.BooleanField(blank=True)
    tab_2 = models.BooleanField(blank=True)
    tab_3 = models.BooleanField(blank=True)
    tab_4 = models.BooleanField(blank=True)
    tab_5 = models.BooleanField(blank=True)
    tab_6 = models.BooleanField(blank=True)
    tab_7 = models.BooleanField(blank=True)
    tab_8 = models.BooleanField(blank=True)
    tab_9 = models.BooleanField(blank=True)

• Pages

class Tabular(Page):
    form_model = 'player'
    form_fields = ['tab_1','tab_2','tab_3','tab_4','tab_5','tab_6','tab_7','tab_8','tab_9']

Tabular (ii)

• Template

  • raw HTML, bs table

{% block content %}

  <table class="table table-bordered">
    <tbody>
      <tr>
          <td><button name="tab_1" value="True" class="btn btn-outline-primary" btn-lg"> 1 </button></td>
          <td> <button name="tab_2" value="True" class="btn btn-outline-primary" btn-lg">2</button></td>
          <td> <button name="tab_3" value="True" class="btn btn-outline-primary" btn-lg">3</button></td>
        </tr>
        <tr>
          <td><button name="tab_4" value="True" class="btn btn-outline-primary" btn-lg">4</button></td>
          <td><button name="tab_5" value="True" class="btn btn-outline-primary" btn-lg">5</button></td>
          <td><button name="tab_6" value="True" class="btn btn-outline-primary" btn-lg">6</button></td>
      </tr>
      <tr>
        <td ><button name="tab_7" value="True" class="btn btn-outline-primary" btn-lg">7</button></td>
        <td><button name="tab_8" value="True" class="btn btn-outline-primary" btn-lg">8</button></td>
        <td><button name="tab_9" value="True" class="btn btn-outline-primary" btn-lg">9</button></td>
<!--    <td><button name="tab_8" value="True" class="btn btn-outline-primary" btn-lg">8</button></td> -->

      </tr>
    </tbody>
  </table>

{% endblock %}

Setting up an individual decision-making task

Our task

• First we investigate individuals’ risk attituted
  • Multiple Price List questionnaire (Holt and Laury 2002)
    • Trade-off between lotteries
• Second we collect pieces of demographic information
  • Age,gender, …

Screens

Instructions

Choices

Outcomes

Final questionnaire

Code

models.py

• Define session constants
  • Outcomes of lotteries in MPL

class Constants(BaseConstants):
    name_in_url = 'MPL'
    players_per_group = None
    num_rounds = 1
    # these are the lottery payoffs, f1 and f2 refer to lottery A and f3 and f4 to lottery B
    f1 = 2.00
    f2 = 1.60
    f3 = 3.85
    f4 = 0.10

• Group and Subsession are empty
  • Typical of one-shot individual decision making

class Group(BaseGroup):
    pass

class Subsession(BaseSubsession):
    pass

models.py (ii)

• In Player class we define the “templates” for data collection
  • MPL table

class Player(BasePlayer):

    # This is for main choices, each variable is one row in the choice table MPL
    HL_1 = models.PositiveIntegerField(choices=[[1, 'A'],[2, 'B']],widget=widgets.RadioSelectHorizontal)
    HL_2 = models.PositiveIntegerField(choices=[[1, 'A'],[2, 'B']],widget=widgets.RadioSelectHorizontal)
    HL_3 = models.PositiveIntegerField(choices=[[1, 'A'],[2, 'B']],widget=widgets.RadioSelectHorizontal)
    HL_4 = models.PositiveIntegerField(choices=[[1, 'A'],[2, 'B']],widget=widgets.RadioSelectHorizontal)
    HL_5 = models.PositiveIntegerField(choices=[[1, 'A'],[2, 'B']],widget=widgets.RadioSelectHorizontal)
    HL_6 = models.PositiveIntegerField(choices=[[1, 'A'],[2, 'B']],widget=widgets.RadioSelectHorizontal)
    HL_7 = models.PositiveIntegerField(choices=[[1, 'A'],[2, 'B']],widget=widgets.RadioSelectHorizontal)
    HL_8 = models.PositiveIntegerField(choices=[[1, 'A'],[2, 'B']],widget=widgets.RadioSelectHorizontal)
    HL_9 = models.PositiveIntegerField(choices=[[1, 'A'],[2, 'B']],widget=widgets.RadioSelectHorizontal)
    HL_10 = models.PositiveIntegerField(choices=[[1, 'A'],[2, 'B']],widget=widgets.RadioSelectHorizontal)

    # This is needed for the instructions
    HL = models.PositiveIntegerField(choices=[[1, 'A'],[2, 'B']],widget=widgets.RadioSelectHorizontal)

    # These variables are collected in the final questionnaire
    sex = models.StringField(widget=widgets.RadioSelectHorizontal(),choices=['Male', 'Female'])
    age = models.IntegerField(choices = range(18,60,1))
    comment = models.TextField(label="Your comment here:")
    like = models.IntegerField(choices=[1,2,3,4,5],widget=widgets.RadioSelectHorizontal)

models.py (iii)

• In Player class we compute the payoffs
  • Typical of individual decision making

"""
... continue
"""
    # Define here the methods associated to Players
    # this method is needed to compute payoffs
    def set_payoff_HL(self):
        #*******************************************
        # select random row and random outcome
        #*******************************************
        self.participant.vars['HL_row'] = random.randint(1,10)
        # select one row randomly for payment (from module random)
        self.participant.vars['HL_random'] = random.randint(1,10)
        # select the number x that defines the outcome of the lottery (if x<=p, outcome is left f1 or f3, otherwise f2 or f4)
        # write it to participant.vars['HL_random']

        #*******************************************
        # select choices in correspondence to random row
        #*******************************************
        choices = [self.HL_1,self.HL_2,self.HL_3,self.HL_4,self.HL_5,self.HL_6,self.HL_7,self.HL_8,self.HL_9,self.HL_10]
        # create a list with all choices of the player (see self)
        self.participant.vars['HL_choice'] = choices[self.participant.vars['HL_row']-1]
        # select from the list the choice in correspondence to the randomly drawn row (notice the offset)
        # write it to participant.vars['HL_choice']

        #*******************************************
        # Compute here the payoffs
        #*******************************************
        if self.participant.vars['HL_random'] <= self.participant.vars['HL_row']:
        # if the random number is smaller equal than the random row
            if self.participant.vars['HL_choice'] == 1: #A
            # if the choice was A
                self.participant.vars['payoff_HL'] = Constants.f1
                # because HL_row is the same as p in the MPL
            else :
            # if the choice was B
                self.participant.vars['payoff_HL'] = Constants.f3
        else:
        # if the random number is slarger than the random row
            if self.participant.vars['HL_choice'] == 1 :#A
                # if the choice was A
                self.participant.vars['payoff_HL'] = Constants.f2
                # because HL_row is the same as p in the MPL
            else :
                self.participant.vars['payoff_HL'] = Constants.f4

        self.payoff = self.participant.vars['payoff_HL']
        # write the payoff to player.payoff

pages.py

• In the instructions we need this because we have a simulation of choice protocol

class Instructions(Page):
    form_model = 'player'
    form_fields = ['HL'] # the demo MPL

• In the main choice page we need to import a for for each row of the MPL table
• We also need the outcomes, retrieved from constants
  • Important to “declare” the variables to display with vars_for_template()

class PageHL(Page):
# which forms are needed from class player
    form_model = 'player'
    form_fields = ['HL_1','HL_2','HL_3','HL_4','HL_5','HL_6','HL_7','HL_8','HL_9','HL_10'] # all 10 options

    # values that are to be displayed (dictionary)
    def vars_for_template(self):
        # retrieve values from constants and store them in a dictionary
        return{
        'f1':Constants.f1,
        'f2':Constants.f2,
        'f3':Constants.f3,
        'f4':Constants.f4
        }

pages.py (ii)

• Before moving to the next page, we compute payoffs
  • See method set_payoff_HL() from models.py
  • This way we compute payoffs only once and not when browser is refreshed

class PageHL(Page):

"""
[...]
"""

    # before moving to next page, compute payoffs (avoids that with refreshing payoffs are recomputed again)
    def before_next_page(self):
        # built-in method
        self.player.set_payoff_HL()# see in models in Player class

pages.py (iii)

• Display outcomes
  • declare them with vars_for_template()
    • retrieve values from participant.vars and “store” them in a dictionary

class OutcomeHL(Page):
# values needed to inform subjects about the actual outcome
    def vars_for_template(self):
        # retrieve values from participant.vars and store them in a dictionary
        return{
        'payoff_HL': self.player.participant.vars['payoff_HL'],#payoff
        'row': self.player.participant.vars['HL_row'], # randomly chosen row
        'value': self.participant.vars['HL_random'],# randomly chosen value to define outcome
        'choice': self.participant.vars['HL_choice'],# actual choice
        # outcomes of the selected row
        'p_A_1': self.participant.vars['HL_row'],
        'p_A_2': 10-self.participant.vars['HL_row'],
        'p_B_1': self.participant.vars['HL_row'],
        'p_B_2': 10-self.participant.vars['HL_row']
        }

pages.py (iv)

• Forms in the final questionnaire retrieved from class player in models.py

class Anag(Page):
# forms to retrieve individual information
    form_model = 'player'
    form_fields = ['comment','like','sex','age']# player.comment, player.like, ...

• Manage the sequence of pages

# the coreography of pages
page_sequence = [
                    Instructions,
                    PageHL,
                    OutcomeHL,
                    Anag
]

Templates

Instructions

• Style elements
  • size of radio buttons

{% extends "global/Page.html" %}
{% load staticfiles otree %}

{% block styles %}
   <style>
      input[type=radio] {
        transform: scale(1.5);
        margin: 12px -10px 0px -30px;
      }
   </style>
{% endblock %}

Instructions.html

• Style elements
  • size of radio buttons

{% extends "global/Page.html" %}
{% load staticfiles otree %}

{% block styles %}
   <style>
      input[type=radio] {
        transform: scale(1.5);
        margin: 12px -10px 0px -30px;
      }
   </style>
{% endblock %}

Instructions.html (ii)

• Main body and demo of MPL
  • In a bs container

{% block content %}

<h1>Instructions</h1>

<div class="container p-3 my-3 border" style="font-size:18pt">
  <h2> Part 1 </h2>

      <p>In the firt part of the experiment you are going to choose between couples of lotteries. </p>

      <p>The following is an example of the decision setting you are facing</p>
      <table class="table">
        <thead>
          <tr>
            <th scope="col">#</th>
            <th scope="col" colspan="2" style="text-align:center">A</th>
            <th scope="col" ></th>
            <th scope="col" colspan="2"  style="text-align:center">B</th>
            <th scope="col"></th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <th scope="row">1</th>
            <td > p/10 of €A<sub>1</sub>  </td>
            <td> (1-p)/10 of €A<sub>2</sub></td>
            <td style="font-weight: bold">{{ form.HL }}</td>
            <td>p/10 of €B<sub>1</sub></td>
            <td >(1-p)/10 of €B<sub>2</sub> </td>
          </tr>
        </tbody>
        </table>

<p>You must choose between lottery A and lottery B, with lottery A delivering €A<sub>1</sub> with probability p/10 and €A<sub>2</sub> with probability (1-p)/10.</p>
<p>Similarly, lottery B delivers €B<sub>1</sub> with probability p/10 and €B<sub>2</sub> with probability (1-p)/10.</p> <p>You will face 10 choices between A and B, with p changing across choices.</p>
<p>All your earnings are virtual, no cash is going to be paid to you. However, choose as if the monetary stakes were real.</p>
</div>

<div class="container p-3 my-3 border" style="font-size:18pt">

<h2> Part 2 </h2>

<p>In the second part of the experiment you are asked to report some information about you.</p>

</div>

Instructions.html

• The button to leave the page
  • Put it to the right with a container

"""
[...]
"""

<div class="container" style="font-size:18pt">
  <div class="row">
    &nbsp;
  </div>
  <div class="row" style="padding-left:135px;">
    <div class="col-md-10">

    </div>
    <div class="col-md-2">
      <button name="btn_submit" value="True" class="btn btn-primary btn-large">
         <span style="font-size:18pt">Continue</span>
     </button>
    </div>
  </div>
</div>


</body></html>

{% endblock %}

How to run and test your app

settings.py

• Add your app to the list SESSION_CONFIGS
  • Description of the app is in a dictionary
    • You can set here other parameters (e.g., treatment) that can be then accessed with session.config

SESSION_CONFIGS = [
 {
      'name': 'MPL',
      'display_name': "MPL",
      'num_demo_participants': 1, # this is the number you want for testing and debugging
      'app_sequence': ['MPL'],
      'language':"en"
  },

  ...
]

Start a you app

• Move to your oTree folder with the terminal (usually cd ~/oTree/)
  • give the command otree devserver
  • copy and paste the url http://localhost:8000/ into you browser
• You will get the following window

Test your app

• To test your app and debug just click on the name of the app
  • This creates a number of links (clients) equal to the value in ‘num_demo_participants’ in settings
  • Click on the link to open a client
    • When a number of clients equal to ‘num_demo_participants’ is open you can start your session

Run a session

• To run a session with N participants
  • Click on Sessions in the top bar menu

  

• Click on Create new session

Run a session (ii)

• Choose you app
  • Configure your settings
    • e.g., number of participants
  • Click on create
    • You will get a number of links equal to number of participants that you can distribute to your clients

Download your data

• To download your data go tp data in the top bar menu

• Click on You can download data in Excel or CSV format here. to download data in an open format
  • You can download data for all your apps or separately for each app

Thank you

🦁

To contact me just write me an email

matteo.ploner@unitn.it

or write me on the forum of the course

Appendix

Assignment

1. Easy
   • Add a field to the final questionnaire
     • Nationality
2. Less easy
   • Change the protocol of the MPL
     • Instead of a choice for each row, participants report only the row in which they switch from A to B
     • e.g., the sequence AAAAABBBBB become 6

OTree code

• The oTree app of this lecture:

Download MPL.zipDownload inputs.zip

References

Holt, Charles A, and Susan K Laury. 2002. “Risk Aversion and Incentive Effects.” American Economic Review 92 (5): 1644–55.