confirmation bias

Confirmation Bias

CCC8001 Logic and Critical Thinking

COURSE REVIEW

Course Instructor

Office: HSH (Ho Sin Hang) 213

Office Hours

Friday 14:00-16:00

My Email

[email protected]

mailto:[email protected]



Course Website

michaeljohnsonphilosophy.com

SUBJECT REVIEW

Critical Thinking

Is there any evidence to support the claim?

Is the evidence reliable and trustworthy? How reliable is it? Should you accept it?

Does the evidence actually support the claim?

Is there other evidence you should consider?

WASON SELECTION TASK

Even vs. Odd

Even numbers: 2, 4, 6, 8, 10, 12…

Odd numbers: 1, 3, 5, 7, 9, 11, 13…

Wason Selection Task

Suppose that I present you with four cards. On each card there is a number on one side and a color (blue or red) on the other. I claim:

If a card has an even number on one side then it is blue on the other side.

Which of the four cards do you need to turn over to tell whether this claim is true or false?

A B C D

Results!

Note

Finding out whether a claim is true or not true is the same thing as finding out whether the claim is false or not false.

• If it’s true, then it’s not false.• If it’s false, then it’s not true.


Card A doesn’t matter. First possibility:

1. The other side is blue. The claim says if it’s even, then it’s blue. It does not say that if it’s not even, then it is not blue.

Example

True claim: if a student makes an appointment, she can see me in my office.

Does not mean false claim: if a student does not make an appointment, she cannot see me in my office.


Card A doesn’t matter. Second possibility:

2. The other side is red. The claim says even cards can’t be red. It does not say odd cards can’t be red.

A B C D


Card D doesn’t matter. Two possibilities:

1. The other side is even (for example, it’s “4”). The claim says if it’s even, then it’s blue. It does not say that if it’s blue, then it’s even.

Example

True claim: If something is a dog, then it is an animal.

Does not mean false claim: if something is an animal, then it is a dog.


Card D doesn’t matter. Two possibilities:

2. The other side is odd (for example, it’s “3”). The claim says if it’s even, then it’s blue. It does not say that if it’s not even, then it is not blue.

A B C D


Card B is important.

4 is an even number. If other side of card B is red, then the claim is false, because B is a card with an even number on one side but it is not blue on the other side.

You must turn over B and make sure it is not red on the other side.

A B C D


Card C is also important.

If the claim is true, this card must have an odd number on the other side. If it has an even number on the other side, then the claim is false.

You must turn over #3 and make sure there is not an odd number on the other side.

Statistical Results

Around ½ of people studied say “B: 4” and “D: Blue”.

About 1/3 say just “B: 4”.

Only about 1/20 get the right answer: “B: 4” and “C: Red”!

Analysis

People look for results that would agree with the claim.

Turning over B and D, you could get agreement– for example, [4, Blue] and [6, Blue].

You cannot get agreement by turning over C. But you can get disagreement and that is why the card is important!

CHERRY PICKING

Cherry Picking

If you see cherries in the store, you might notice that most or all of them were ripe and healthy.But you couldn’t conclude that most or all cherries are ripe and healthy. These ones have been selectively picked for good condition.

Fluoride and Oral Health

Fluoride is a chemical that is known to prevent tooth-decay. It is in most toothpastes and many places in the world put it in the drinking water. The US CDCP says water fluoridation is “one of 10 great public health achievements of the 20th century.”

Precious Bodily Fluids

Some people have decided that fluoridation of the water is bad. In the 1950’s US, some thought it was a communist conspiracy. Now some people think it’s a conspiracy of the UN or the “New World Order” or whatever.

Cherry Picking

“The 2011 figures show little difference [in cavity-free 5 year olds], with the rate for fluoridated areas being 59.91% and that for non-fluoridated areas being 59.18%.”(See course website for reading.)

% Cavity-Free

Decayed, Missing, Filled Teeth

CONFIRMATION BIAS

Confirmation Bias

People tend to look for evidence that agrees with what they already believe.

This is called confirmation bias.

Bacon on Confirmation Bias

“The human understanding when it has once adopted an opinion… draws all things else to support and agree with it. And though there be a greater number and weight of instances to be found on the other side, yet these it either neglects and despises, or else by some distinction sets aside and rejects; in order that by this great and pernicious predetermination the authority of its former conclusions may remain inviolate.” – Sir Francis Bacon

Confirmation Bias

“Confirmation bias is perhaps the best known and most widely accepted notion of inferential error to come out of the literature on human reasoning.” (Evans, 1989, p. 41)

Confirmation Bias

“Many have written about this bias, and it appears to be sufficiently strong and pervasive that one is led to wonder whether the bias, by itself, might account for a significant fraction of the disputes, altercations, and misunderstandings that occur among individuals, groups, and nations.” – Nickerson 1998

It’s Ordinary

“Your day might start on a sour note: you wake up late, the barista screws up your coffee (even after you’ve waited forever in line), your car won’t start again. If you mentally set yourself up to say “This is a bad day,” you will look for further evidence to support that notion throughout your day, potentially ignoring evidence that it’s a day like any other or maybe even a good day overall.” -- Satya Putumbaka

Fish vs. Obama

“There’s no mistaking what’s going on in the speech delivered last week. No preliminary niceties; just a rehearsal of Obama’s actions and expectations. Eight ‘I’’s right off the bat:”-- Stanley Fish

“I”s

“Just over two months ago I spoke with you… ““and I laid out what needed to be done.” “From the beginning I made it clear that I would not put any more tax dollars on the line.” “I refused to let those companies become permanent wards of the state.” “I refused to kick the can down the road.”“But I also recognized the importance of a viable auto industry.” “I decided then…”

Presidential PronounsUS President “I” “me” “my” Total

Obama1st Press Conf.

2.10% 0.55% 2.65%

Bush Jr.1st 2 Press

Conf.

3.58% 0.91% 4.49%

Clinton1st 2 Press

Conf.

3.14% 0.73% 3.87%

Stereotypes

Stereotypes are another instance where our expectations lead us into the wrong beliefs.

Gender stereotype: women are bad at math.

Bad at Math = Yes

Bad at Math = No

Woman = Yes A BWoman = No C D

Confirmation Bias

Bad at Math = Yes

Bad at Math = No

Woman = Yes 20 BWoman = No C 50

The Red Card Matters!

Bad at Math = Yes

Bad at Math = No

Woman = Yes 20 40Woman = No 25 50

Confirmation bias also helps us ignore those times when we are stereotyping others.

Anecdotes ≠ Data

A Strange Example

Americans were asked:

Which of these pairs of countries are more similar to one another?

1. West Germany, East Germany2. Sri Lanka, Nepal

A Strange Example

A Strange Example

They said (1), West Germany and East Germany. Others (Americans) were also asked:

Which of these pairs of countries are more different from one another?

1. West Germany, East Germany2. Sri Lanka, Nepal

A Strange Example

They also said (1).

Americans thought that West Germany and East Germany were both more similar to each other than Sri Lanka and Nepal and less similar to each other than Sri Lanka and Nepal.

How is that possible?

First, when considering the question ‘which are more similar?’ the subjects looked for all the positive evidence that West Germany and East Germany were similar, and all the positive evidence that Sri Lanka and Nepal were similar.

Since Americans know nothing about Asian countries, they had no positive reason to think Sri Lanka and Nepal were similar.

Similarly, when asked ‘which are more different?’ the subjects considered the positive evidence that West Germany and East Germany were different and the positive evidence that Sri Lanka and Nepal were different.

Again, having no knowledge of Sri Lanka or Nepal, Americans chose (1), because of all the positive evidence in its favor.

But it cannot be true that East Germany and West Germany are both more similar and more different than Sri Lanka and Nepal.

What the subjects did not do is consider the relevant negative evidence that would disconfirm their hypotheses.

ABSENT DATA

The Problem of Absent Data

Sometimes it’s not just that we only look for or evaluate the positive evidence, but that there is no negative evidence. This can lead us to think we have very well-confirmed beliefs when we do not.

Hiring Job Applicants

Suppose you’re hiring job applicants for your shoe company. You think people who haven’t studied a musical instrument would not be good employees.

Who do you hire? The people who have studied music, of course! And if they’re successful at your company, do you have good reason to believe that you were right?

No! You have positive evidence– people you predicted would be successful, who are successful– but you have no negative evidence.

What about all the people you didn’t hire, the ones who didn’t study music? They might have been successful too. They could’ve been more successful. You don’t know.

Absent evidence is all around us.

Suppose you decide to major in accounting instead of philosophy. You find that you are very happy studying accounting. Did you make the right choice? You can’t know. You could have been more happy studying philosophy. There’s just no evidence.

The Echo Chamber

Data can be absent also because we make it so: we put ourselves in a position to never hear people who disagree with us.

The Echo Chamber

confirmation bias

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