Trust

Defining Trust

In Class Exercise: What are things you would do with someone you trust, but would not do with someone you don’t trust? Loan money Ask for a movie / restaurant / hotel recommendation Tell a secret Ask for a recommendation letter or for a reference Ask for advice Ask the person to take care of my pets / house while I am

away Lend my car Go on a trip

Why trust?

Loan money - We expect the person will pay us back

Ask for a recommendation - The person's recommendation will match our taste and the movie or restaurant or hotel will be good.

Tell a secret - The person will keep a secret, not tell others, and not judge us for it.

Ask for a recommendation or reference - The recommendation will be positive and help us get the position we are applying to.

General Definition

Trust is putting oneself in a vulnerable position based on the belief that another person will act with our best interest in mind.

Categories of Trust

Trust with material possessions

Belief about reliability

Trust with secrets

Trust regarding physical safety

Johnson-George and Swap (1982)

How Trust Develops

Calculation-based trust – A rational decision about whether to trust someone, where the costs and benefits of trusting are factored in.

Personal-based trust – A person's propensity to trust, developed over the course of their life.

Cognition-based trust - The instant rapport and trust that can develop between people who share similar backgrounds, beliefs, and values. It often is based in first impressions.

Institution-based trust - How trust may form in the presence of guarantees and protections offered by an institution.

Trust Asymmetry

Trust is not always equal between people

Extreme example: parents and children A child must have almost complete trust in his

parent while the parent should have very little trust in a child (on substantive matters)

More common asymmetries are smaller E.g. Bosses and employees Employees tend to trust superiors more

Context and Time

Trust changes over time

Trust will vary among contexts I may trust Bob to recommend a restaurant, but not

to dog sit

Trust can also transfer between contexts I trust Bob from knowing him at work, and so I will

trust him to water my plants if I ask (even though I have no basis for trusting his plant responsibility)

Measuring Trust

Some people are more trusting than others. This is called a propensity to trust

This can be measured with a simple thought experiment called the Investment Game

The Investment Game

You are given $10. You can keep it all or invest some (or all) of it with an unknown person.

Whatever you choose to invest is tripled and given to the unknown person. E.g. If you invest $5, they get $15. If you invest $10,

they get $30

That person can keep it all, or return any amount of it to you as a return on your investment.

How much do you invest?

Trustworthiness

We can compute trustworthiness with the same game by asking how much money you would return if you receive the investment.

A great survey by Evans and Revelle (2008) also measures trustworthiness. Take it and see where you fall on the scales

Trust in Others

The investment game can be repeated for specific other people instead of strangers

Other surveys to measure trust. Examples: Overall Trust

If we decided to meet somewhere for lunch, I would be certain ______ would be there.

I could expect _____ to tell me the truth.

Emotional Trust I could talk freely to ____ and know he/she would want to listen. _____ would never intentionally misrepresent my point of view to others.

Reliability If my alarm clock was broken and I asked ______ to call me at a certain

time, I could count on receiving the call. If I were injured or hurt, I could depend on _____ to do what was best for

me.

Trust in Social Media

Apply these same estimates to people we know online

Ask people explicitly to rate trust in others E.g. Epinions

Issue: most people online are strangers

Trust Inference

Infer trust between two unknown people using network structure

If A-B have trust, and B-C have trust, how much should A trust C?

A B CtAB tBC

tAC

Trust Inference Algorithms

Use network structure to infer trust

Example approach Find neighbors who are trusted. Ask them how much to trust the stranger. Average their responses weighted by how much we

trust each neighbor. Neighbors repeat this if they do not know the

stranger.

Inferring over many paths

SourceSink

B

A

E

D

C

I

H

F

G

8

7

3

9

5

8

6

10

49

2

1

9

8

5

3

Applications of Trust

Once trust is computed, how can we use it? Filtering information

e.g. show reviews only from the most trusted people Sorting Information

Show Facebook posts from my most trusted friends first, and least trusted friends last

Aggregating Information Give more weight to restaurant ratings from

trustworthy people and less weight to lower-trust people when computing an average rating.

Brainstorming

Think of examples of places you interact with user-generated content online.

If you could compute how much to trust the person responsible for each post, how would you use that to help you?

Conclusions

Trust has an element of risk and belief in another person.

There are many ways to estimate trust users have in their friends.

In social media, we want to know how much to trust strangers and there are computational methods to do that.

Trust can be used to improve the way people interact with information in social media.