Credibility

Chapter 4Chapter 4

How believable is a claim?

How credible is a source?

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Not an all-or-nothing thing!

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Statements/sources vary incredibility.

For example:For example:

“The teacher owns a duck.”

“The teacher owns a dump truck.”

“The teacher owns a hippopotamus.”

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Why is it harder to believe theWhy is it harder to believe theteacher owns a hippopotamus?teacher owns a hippopotamus? It raises more questions.

How’d she get one?

Where does she keep the sucker?

Say—isn’t it illegal to keep a hippo?

Etc.

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In short:In short:

The idea of the teacher owning ahippo conflicts with your “backgroundknowledge.”

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Roy

alty

-Fre

e/C

OR

BIS

“Mr. Zingg drinks a pint of sulfuricacid each night before bed.”

““BelievableBelievable”” is NOT entirely is NOT entirelysubjective:subjective:

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Which is most UNBELIEVABLE?Which is most UNBELIEVABLE?

Teacher is under 20 years old.

Teacher is under 55 year old.

Teacher is under 90 years old.

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Which is LEAST unbelievable?Which is LEAST unbelievable? They’ve taught crows how to play checkers.

W. arranged 9/11 so he could invade Iraq andget its oil.

Dr. Moore is related to George Washington.

Bigfoot exists.

We have been visited by space aliens. Some ofthem are taking this class.

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Which is MOST unbelievable?Which is MOST unbelievable?

Obviously:Obviously:

The more unbelievable the claim,the stronger the argument you needto accept it.

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For example:For example:

“Dean Stooler can runa mile in less thanfour minutes.”

“Dean Stooler can runa mile in less thanseven minutes.”

More is required toestablish the firststatement.

12

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Watch out for things you acceptWatch out for things you acceptjust because youjust because you’’ve heard themve heard them

so often:so often:

A critical thinker will want EVIDENCEbefore accepting “what everyoneknows.”

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Old wivesOld wives’’ tales? tales?

Daddy long legs are the world’s most poisonousspider.

Eating carrots makes you see better.

Aspirin with Coca-Cola will make you drunk.

Pop Rocks followed by Pepsi can make yourstomach explode.

Going outside with wet hair will give you a cold.

(more…)

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Old wivesOld wives’’ tales? tales?

Reading in dim light will hurt your eyes.

Too much TV will hurt your eyes.

Chocolate causes pimples.

Coffee stunts your growth.

Crossing your eyes can make you cross-eyed.

Cracking your knuckles causes arthritis.

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Credibility of SourcesCredibility of Sources

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Two kinds of doubt:Two kinds of doubt:

1. Doubts about a source’s knowledge

2. Doubts about a source’s truthfulness,objectivity, reliability

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““SmittySmitty knows a lot, but you knows a lot, but youcancan’’t trust a word he says.t trust a word he says.””

““SmittySmitty never lies, but he never lies, but hedoesndoesn’’t know a thing.t know a thing.””

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Either way, Smitty isn’t the best source.

Q: Can you tell if a person (notsomeone you know) is lying toyou?

Are there any tell-tale clues?

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Excessive sweating?

Shifty eye movement/avoiding eye contact?

Staring up to the left/other micro-expressions?

Wimpy handshake?

Changing the subject?

Appearing lacking in self-confidence?

Nervous laughter?

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If any of these were at allIf any of these were at allreliable, we wouldnreliable, we wouldn’’t needt need

courts, ID checks, liecourts, ID checks, liedetectors, blah detectors, blah blahblah blahblah……

Why would teachers take precautionsagainst cheating, if they could just

look at a kid and tell?

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Need four volunteers!

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A more scientific experiment:Need just two volunteers…

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Here are your Here are your ““votingvoting”” options. options.

T/T: Bothtellingtruth

L/L: Bothlying

T/L: Firstpersontruthful;second islying

L/T: Firstpersonlying;second istruthful

Even a truthful source can:Even a truthful source can:

Make MISTAKES

Be BIASED

LACK EXPERTISE

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How to judge a person’s expertise?

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Self-confidence/nervousness?

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Clothes?

Posture?

Accent?Gender?

Nationality?

Those all seem prettyunreliable.

Anyone can LOOKlike an authority…

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Height?

http://news.bbc.co.uk/2/hi/health/3200296.stm

How would YOU makeHow would YOU makesomeone look like a scientist?someone look like a scientist?

Use a stereotype!

White lab coat or poor-fitting suit

Pocket protector

Glasses; thick

Gray hair

German/British accent, etc.

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Conclusion:Conclusion:

ItIt’’s difficult to measure as difficult to measure apersonperson’’s expertise by looking ats expertise by looking at

him or her.him or her.

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BEST indicators of a sourceBEST indicators of a source’’ssknowledge are these:knowledge are these:

Education

Experience

Reputation

Position

Achievements

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Does being an expert in one fieldDoes being an expert in one fieldmake you an expert in another field?make you an expert in another field? Not if the two fields aren’t related.

An expert in economics doesn’t automaticallyqualify as expert in, say, political science.

An expert in oceanography shouldn’t beassumed to be an expert in genetics.

Your business prof can’t be assumed to haveexpert knowledge of history.

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A common mistake:A common mistake:

To attach EXTRA authority to what someone saysJUST because he/she:

Is your parent

Is your friend

Is your teacher

(Being a TEACHER carries extra weight in theperson’s field, but the fact he/she is YOUR teacherdoesn’t add anything.)

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Other sources:Other sources:

Newspapers; other print media

Electronic media; TV, radio

The Internet is actually a source ofsources, not a source in itself.

University publications

Government publications

Professional journals35© 2009 McGraw-Hill Higher Education. All rights reserved.

An example of an unreliableAn example of an unreliablenews sourcenews source……??

The weekly rag available in thecheckout line.

REDNECK ALIENS TAKE OVERREDNECK ALIENS TAKE OVERTRAILER PARK!TRAILER PARK!

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A much better source:A much better source:

The website of the Sacremento Bee

http://www.sacbee.com/

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Even better (because moreEven better (because morecomplete):complete):

The New York Times newspaper

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One final ideaOne final idea……

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Sometimes you get anSometimes you get anunbelievable claim comingunbelievable claim coming

from a credible source.from a credible source.

Like, say, from a friendor a relative.

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Like, I had an aunt who wasLike, I had an aunt who wasconvinced she saw a ghost.convinced she saw a ghost.

Good old Aunt Rose…she had noreason to lie, and she was as

honest as the day is long.

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This brings us to HumeThis brings us to Hume’’ssprinciple.principle.

Hume?

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David HumeDavid Hume

David Hume(1711-1776), anice chap. Likedto play whist.Here’s what hesaid…

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© L

ibra

ry o

f Con

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s

HumeHume’’s principle:s principle:

“No testimony is sufficient to establisha miracle, unless the testimony be ofsuch a kind, that its falsehood wouldbe more miraculous than the fact itendeavors to establish.”

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“When anyone tells me he saw a deadman restored to life, I consider whether itbe more probable that this person shouldeither deceive or be deceived, or that thefact he relates should really havehappened. I weigh the one miracleagainst the other; and always reject thegreater miracle. If the falsehood of histestimony would be more miraculousthan the event which he relates, then,and not till then, can he pretend tocommand my belief or opinion.”

“When anyone tells me he saw a deadman restored to life, I consider whether itbe more probable that this person shouldeither deceive or be deceived, or that thefact he relates should really havehappened. I weigh the one miracleagainst the other; and always reject thegreater miracle. If the falsehood of histestimony would be more miraculousthan the event which he relates, then,and not till then, can he pretend tocommand my belief or opinion.”

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