Workshop: Science Meets Industry: Online Behavioral Experiments with nodeGame - Stefano Balietti, Northeastern University

Online Behavioral Experiments
with NodeGame
Stefano Balietti
Network Science Institute, Northeastern University
Harvard Institute for Quantitative Social Science
D'Amore McKim School of Business, Northeastern University
@balietti | @nodegameorg | stefanobalietti.com | nodegame.org

1. Become confident about the principles and the methodology
behind social science scientific experiments
2. Get a quick-start with the software nodeGame to conduct
experimental research online
Goals of the Workshop

Workshop Instructors
Me
Social Scientist Open Source
Developer

Me
Social Scientist
Open
Source
Developer

An experiment is a methodological procedure carried out with the
goal of verifying, falsifying, or establishing the validity of a hypothesis.
A test under controlled conditions that is made to demonstrate a
known truth, examine the validity of a hypothesis, or determine the
efficacy of something previously untried.
An experiment is an empirical method that arbitrates between
competing hypotheses.
What is an experiment?

Internal validity:
The extent to which a causal inference based on a study is
warranted by an experiment.

Control
3 Pillars of Experimental Design
RandomizationIndependence

Control
RandomizationIndependence
Deliberate choice of the variables
that will be kept constants and those
that will be varied: treatment variables

Control
Randomization
Independence
Treatment variables must not be correlated

Control
Randomization
Independence
Participants are randomly assigned to conditions
Conditions are executed in random order
Stratification might be required

Internal validity:
The extent to which a causal inference based on a study is
warranted by an experiment.
External validity:
The extent to which the results of a study can be generalized
or extended to others.

Galileo's hand-made drawing of the moon surface. Sidereus Nuncius (1610)
External Validity

External Validity
Telescope:
From Land to Sky

External Validity
Telescope:
From Land to Sky
Experiments:
From Lab to Real Life

Super-brief history of scientific experiments

• Novum Organum (1620)
• Scientific induction
• Torturing Nature to extract her secrets
Super-brief history of scientific experiments (1/3)

• Novum Organum (1620)
• Scientific induction
• Torturing Nature to extract her secrets
Ever heard of Phlogistons??

“There is a property common to almost all
the moral sciences, and by which they are
distinguished from many of the physical;
that is, that it is seldom in our power to
make experiments with them”
John Stuart Mill, 1836

“There is no laboratory in which economists can test
their hypothesis”
, 1993
Super-brief history of scientific experiments (2B/3)

Nobel prize for Vernon Smith
“for having established laboratory
experiments as a tool in empirical
economic analysis, especially in the
study of alternative market mechanisms”
2002

The Ultimatum Game
Rules:
• 2 Players (A,B)
• 100 $

The Ultimatum Game
Rules:
• 2 Players (A,B)
• 100 $
• Player A makes a proposal

The Ultimatum Game
Rules:
• 2 Players (A,B)
• 100 $
• Player B can accept or refuse the split.

The Ultimatum Game
Rules:
• 2 Players (A,B)
• 100 $
• If B accepts each one gets his/her
share.

The Ultimatum Game
Rules:
• 2 Players (A,B)
• 100 $
share.
• If B refuses both players get nothing.

The Ultimatum Game: How to Split 100$
Rules:
• 2 Players (A,B)
• 100 $
share.
• If B refuses both players get nothing.

A B

Proposer Respondent
RationalRational

Proposer Respondent
I say 99 for me
and 1 for you.
RationalRational

Proposer Respondent
I say 99 for me
and 1 for you.
RationalRational
I say OK.

Human Being Human Being
I say 99 for me
and 1 for you.

Human Being Human Being
I say…$!!@**
I say 99 for me
and 1 for you.

Nowak (2006) 5 rules for Cooperation

Traditional Laboratory Research
• Decision making tools, heuristics, models of human behavior

• BUT

• BUT
• Small groups of individuals, generally 4-12 (bounded by uni. Lab)

• BUT
• Behavior of individuals in social networks under-researched

• BUT
• Limited in the number of hypotheses that can be tested

• BUT
• Observations are limited in time

• BUT
• Limited(?) external validity

• BUT
• Limited(?) external validity
• Generally high costs for an academic budget

The Present/Future of
Behavioral Research

Me
Social Scientist
Open Source Developer

Install nodeGame 3.x
1. Go to http://nodegame.org
2. Click on the “Get Started” button
3. Follow instructions to install Development version
4. Keep following my talk!

nodeGame 3.x Architecture Overview

nodeGame 3.x Architecture Overview
~46.000 lines
(including comments)

Launch nodeGame 3.x
Open a terminal and browse to the nodegame folder
Start the server with the command: node launcher.js
Open a browser and access the default ultimatum game at the url:
localhost:8080/ultimatum
Start an automated player (bot) at the url:
localhost:8080/ultimatum?clientType=autoplay
Access the administrator interface at the url:
localhost:8080/ultimatum/monitor/

Create a New Game
cd nodegame/bin/
node nodegame create-game gamename <author> <email>
Creates a new game in the games/ folder (usually nodegame/games/)
Important! Windows users must install the nodegame-generator package
manually from the git repository (or npm)
git clone https://github.com/nodeGame/nodegame-generator.git
cd nodegame-generator
npm install

Anatomy of a Game
Features:
- Define game variables and treatments
- Define the game sequence with the Stager API
- Implement the game sequence into client types

The Game Sequence and Client Types
Game Sequence Client Types
stager.stage("instructions")
.step("instructions_1")
.step("instructions_3");
stager.stage("quiz");
stager.repeat("game", 3)
stager.stage("questionnaire");
stager.extendStage("game", {
steps: ["offer", "respond",
. "display_results"]
});
Code Snippet

stager.stage("instructions")
.step("instructions_3");
stager.stage("quiz");
stager.repeat("game", 3)
stager.stage("questionnaire");
steps: [ "offer", "respond",
. "display_results" ]
});
Code Snippet

Client types implement the game sequence
by extending its steps and stages.

Game Sequence Client Types Code Snippet
stager.setDefaultProperty("coins",100);
coins: 200
});
stager.extendStep("offer", {
coins: 50
});

Game Sequence Client Types Code Snippet
stager.setDefaultProperty("coins",100);
coins: 200
});
stager.extendStep("offer", {
coins: 50
});
node.game.getProperty("coins") returns 50 in
step 'offer', 200 in steps 'respond' and 'display results'
inside the 'game' stage, and 100 in any other step.
Step/Stages Properties are hierarchical

Some Built-in Step-Properties
Property Description Type
init Executed upon entering the step/stage function
exit Executed upon exiting the step/stage function
timer Sets the maximum execution time for step (ms) number
timeup Executed if the timer expires function
done Executed when the step terminates function
cb The actual step execution function

Logic Client Type
Executed on the server, governs a game room
- Makes groups
- Keep track of game history
- Handles disconnections and reconnections
- Access to:
- internal Database NDDB: node.game.memory
- player list: node.game.pl
- channel and registry object

Player Client Types
Executed on a client, e.g. a browser
- Display/manipulate information on screen
- Exchange messages with the server and other players
- Respond to user events
- Determine when the current step is finished (“done”)
W (Window): manipulates information on screen and the behavior of user interface,
e.g. disabling right click, locking screen, etc.
At the end of each step, the game developer must call the method
node.done, which triggers a procedure that advances the client to the next step.

Inside a Step Callback Function
Instructions Step
- Player client type
- No interaction with other players
- No interaction with the page
- No time limit
- Simply click “Done” when
finished reading and advance to
next step

stager.extendStep('instructions_1', {
frame: "instr1.htm"
});
Instructions Step
- No time limit
next step

frame: "instr1.htm"
});
Widget Step
- No interaction with other players (at
the moment)
- Standardized interaction
- With or without time limit
- Register the mood of the participant
using the PANAS method.
Instructions Step
- No time limit
next step

frame: "instr1.htm"
});
Widget Step
- No interaction with other players (at
the moment)
- Standardized interaction
- With or without time limit
- Register the mood of the participant
using the PANAS method.
Instructions Step
- No time limit
next step
widget: "MoodGauge"
});

Roles (version 3.5 dev)
stager.extendStep('bidder', {
matcher: {
// Available roles.
roles: [ 'BIDDER', 'RESPONDENT'],
// Each player is matched with a
// partner and is assigned a role.
match: 'roundrobin',
// How to continue matching after
// all combinations are exhausted
cycle: 'repeat_invert'
}
});
Logic Client Type

Roles (version 3.5 dev)
roles: {
BIDDER: {
frame: 'bidder.htm',
cb: function() {
// Bidder stuff.
}
},
RESPONDENT: {
frame: 'resp.htm',
cb: function() {
// Respondent stuff.
}}}
});
Player Client Type
matcher: {
// Available roles.
roles: [ 'BIDDER', 'RESPONDENT'],
// Each player is matched with a
// partner and is assigned a role.
match: 'roundrobin',
// How to continue matching after
// all combinations are exhausted
cycle: 'repeat_invert'
}
});
Logic Client Type

Inside the Step Callback Function
// The respondent receives the offer,
// displays it, and terminates the step.
// On incoming data labeled "offer",
// executes the function.
node.on.data("offer", function(msg) {
// Display offer using W.
W.setInnerHTML("offer", msg.data);
// End step.
node.done();
});
// Player made a choice
// and clicked the submit button.
submit.onclick = function() {
// Send offer to respondent.
node.say("offer", "respondent", 1);
// End step, store offer in server.
node.done({ offer: 1 });
};
I say 99 for me
and 1 for you.
Proposer Respondent

NDDB: Internal Database
// The respondent receives the offer,
// displays it, and terminates the step.
// On incoming data labeled "offer",
// executes the function.
node.on.data("offer", function(msg) {
// Display offer using W.
W.setInnerHTML("offer", msg.data);
// End step.
node.done();
});
// Player made a choice
// and clicked the submit button.
submit.onclick = function() {
// Send offer to respondent.
node.say("offer", "respondent", 1);
// End step, store offer in server.
node.done({ offer: 1});
};
I say 99 for me
and 1 for you.
Proposer Respondent
Logic Client Type
NDDB database
node.game.memory

// Set an object in memory explicitly.
node.set({ foo: "bar" });

{
stage: {
stage: 2,
step: 1,
round: 1
},
player: "respondent",
timestamp: 1480336721939
offer: 1, // foo: "bar"
// node.done specific.
timeup: false,
time: 4321, // from step.
done: true
};

var m = node.game.memory; // NDDB instance.
// Lazy loading.
m.select("player", "=", "respondent");
m.and("stage.step", "=", 1)
.and("offer")
.fetch()[0];
// Use indexes.
m.player["respondent"].last();
m.stage["2.1.1"].select("offer").fetch()[0];
{
stage: {
stage: 2,
step: 1,
round: 1
},
player: "respondent",
timestamp: 1480336721939
offer: 1, // foo: "bar"
// node.done specific.
timeup: false,
time: 4321, // from step.
done: true
};

// Modify database items upon inserting them.
node.game.memory.on("insert", function(item) {
// Decorate item or save it somewhere else.
});
// Disable internal database completely.
// Remove default event listener.
node.off('in.set.DATA');
// Add new one.
node.on('in.set.DATA', function(msg) {
// Save msg somewhere else, e.g. Mongo.
});
Event Listener
Manager
node.game.events

Events in nodeGame 3.x
Internal: generated by the game or by the nodeGame engine.
Incoming: triggered by incoming messages, 'in.[target].[action]', ‘in.set.DATA’

// Registering an internal event listener.
node.on('LOCAL_EVENT', function(a, b) {
// This is local event.
});
// Triggering a local event.
node.emit('LOCAL_EVENT', 1, 2);

// Registering an internal event listener.
node.on('LOCAL_EVENT', function(a, b) {
// This is local event.
});
// Listening for incoming DATA msgs.
node.on('in.say.DATA', function(msg) {
// I got a data msg!
});
// Listening for incoming "foo" DATA msgs.
node.on.data('foo', function(msg) {
// I got a data msg labeled "foo"!
});
node.emit('LOCAL_EVENT', 1, 2);
node.say('foo', "bar");

Events are hierarchically organized, where you register your event matters!

});

});
Valid only in Quiz stage

});
Registered in init or cb function of Step 3.3
Valid only in step 3.3 (any round).

});
Registered in the init function of “Game”
Valid throughout all steps of “Game” stage

How to register a listener valid throughout all
the game?

stager.setInitCb(function() {
});
});
How to register a listener valid throughout all
the game?
In the init function of the game!

Recruiting Participants
Free Platforms
Psychological Research on the Net
http://psych.hanover.edu/research/exponnet.html
The Web Experiment List
http://www.wexlist.net
Online Social Psychology Studies
http://www.socialpsychology.org/expts.htm
Volunteer Science
http://www.volunteerscience.com

Recruiting Participants
Commercial Platforms
ODesk, Freelancer, Elance, Guru, CrowdFlower, Innocentive, SurveySampling,
UpWork …
Most used in research:

How To Run a Game on AMT:
The Big Picture
1. Upload nodeGame server + game to a server
e.g. Heroku cloud: https://github.com/nodeGame/nodegame-heroku
2. Create a new HIT on Amazon Mechanical Turk (AMT), e.g. using the requester
interface or other service API.
3. Use the nodegame-mturk package
https://github.com/nodeGame/nodegame-mturk/
to handle:
- Connection and authentication from AMT HIT page to nodeGame server.
- Opening/expiring/extending HIT while running it.
- Payments, bonuses and qualifications after HIT is done.

Known Issues Conducting
Synchronous Experiments on AMT
1. Not a survey or classification task, need to have DIFFERENT
people at the same time on your platform

2. Btw, not too few, not too many

3. Waiting time in the waiting room should be limited and
homogenous across participants

4. Demographics should be stratified as much as possible

5. Participants should not re-take the same experiment again

6. Dropouts rate (non-completing the HIT) signigicantly affects the
whole experiment, increasing costs $$ and time to complete it

Pay minimum wage (at least). Make bonus dependent on
performance

Rule of thumb: 2.8 times desidered number of participants
Expire HIT as soon as desired number of participant entered
the experimental pipeline (+small buffer)
3x

Rule of thumb: 2.8 times desidered number of participants
Expire HIT as soon as desired number of participant entered
the experimental pipeline (+small buffer)
Dispose participants who waited too long (compensated)

Waiting room can group players based on features
Collect some demographics features in a pre-experimental part
Start 2 (or more) groups at the same time

Create one HIT (no group) with 3x rule
Keep track of turker ids (nodegame-mturk)
Assign qualification via AMT API (nodegame-mturk)

6. Rate of dropouts (non-completing the HIT) significantly affects the
• Make sure waiting time is not too long (previous advices)

• Inform about required time BEFORE and DURING experiment

• Design experiments that are robust to dropout (as much as
possible). For example, use shares instead of fixed quantities.

• Use requirements checkings.

• Use requirements checkings.
• Use “seriousness checks” and “warm-up” phases.

AMT
How To Run a Game on AMT
AMT HIT

Not Just Experiments,
also Gamification
• Industry: lots of A/B testing and customer surveys
• Gamification: applies elements of game playing to solve
complex and simple problems
• Increasing trend
• Improve engagement and understanding
• Fun
• Generate More and Better Ideas
• Train Machine Learning Algorithms
(http://quickdraw.withgoogle.com)

Contributions Welcome!
• Using it, request features, report bugs
• Help developing
• Extremely well documented source code

Thank You!
@balietti | @nodegameorg | stefanobalietti.com | nodegame.org

Workshop: Science Meets Industry: Online Behavioral Experiments with nodeGame - Stefano Balietti, Northeastern University

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Workshop: Science Meets Industry: Online Behavioral Experiments with nodeGame - Stefano Balietti, Northeastern University