FalsifiabilityFalsifiability

• One requirement for a valid scientific theory is that it satisfies the Falsifiability criterion

• Predictions derived from it could potentially be shown to be false.

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PsychicsPsychics

• If prediction is right, you believe they are truly psychic• If prediction is wrong, shrug it off thinking they can’t

be right all the time• There’s no way to show that its false to believe in this

person’s psychic ability• Note: most psychics make such vague predictions that

they are always right, their predictions can explain anything

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The Girl with X-ray EyesThe Girl with X-ray Eyes

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Natasha Demkina: • 17 y/o girl from Russia claims to be able to ‘see’ medical illnesses that doctors miss• Mother claims she is 100% accurate• Makes a pretty good living!

• Tested by Committee for the Scientific Investigation of Claims of the Paranormal (CSICOP) for a Discovery Channel Documentary

Testing the Girl with X-ray EyesTesting the Girl with X-ray Eyes

• 7 volunteers, 6 with known medical conditions and 1 in perfect health

• Given list of ailments, just had to match them to the correct person

• Refused use of fabric screen

• Everyone agreed to the criteria = Correctly ID 5 of 7

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The Girl with Normal EyesThe Girl with Normal Eyes

• She only got 4 right

• Missed the man with the

metal plate in his skull- thought he

was the one missing his appendix

• Took 4 hours to complete the test

• Reading on journalist: many vague/misread symptoms, missed true ailments

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Martians in your headMartians in your head

• Someone in this class told me that Martians live in his head.

• If you X-ray his head and show no Martians, he says they're invisible to X-rays.  If you open his head up surgically and see no Martians, he says they disappear when exposed to oxygen. 

• No matter what test you come up with, you never show any evidence of the Martians in his head, but that makes no difference.  He always has an explanation. 

• His idea about the Martians cannot be falsified and therefore is not scientific.

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Karl PopperKarl Popper

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• Developed the idea of

falsifiability as a criterion

for scientific research

• “the criterion of the scientific status of a theory is its falsifiability, or refutability, or testability”

1902 - 1994

Violating FalsifiabilityViolating Falsifiability

• Theories that are so vague they can explain anything (ex. Psychic readings – P.T. Barnum Effect)• The more specific a theory it is, the more likely

it is falsifiable (Knocking Rhythms)

• Theories that multiple ‘outs’• Ex. Martians in my head disappear when

exposed to oxygen

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Freud & FalsifiabilityFreud & Falsifiability

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• Psychodynamic theory failed the falsifiability criterion

• It explains things after the fact, but does not predict behavior (Tourette’s)

Freud & FalsifiabilityFreud & Falsifiability

• “Psychoanalytic theorizing of this kind in effect leaves no base untouched. Tics are a conversion symptom but not hysterical, anal but also erotic, volitional but also compulsive, organic but also dynamic in origin… These papers, because of their subsequent widespread influence, had a calamitous effect on the understanding and treatment of this syndrome”

• Psychodynamic theories can explain everything and are therefore scientifically useless

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Confirmation of a TheoryConfirmation of a Theory

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• Not all confirmations are created equal• More impressive when the confirmation is of a

risky prediction (30 y/o female vs under 100)

• While replication is important, quality of the replication must be considered

Its OK to be Wrong!Its OK to be Wrong!

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Risky & specific

UncertaintyUncertainty

• Psychological scientists are at the front line of uncertainty• Pro: this is where the interesting questions are• Con: makes us look ‘uncertain’ to the public

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