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CONFIRMATION BIAS. Confirmation Bias: A Ubiquitous Phenomenon in Many Guises Raymond Nicholson, TUFTS Review of General Psychology 50+ pages non-technical 7 full pages of references Francis Bacon (1620) “…great and pernicious predetermination…” Poyla (1954)

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slide2
Confirmation Bias: A Ubiquitous Phenomenon in Many Guises
    • Raymond Nicholson, TUFTS
    • Review of General Psychology
    • 50+ pages
    • non-technical
    • 7 full pages of references
  • Francis Bacon (1620)
    • “…great and pernicious predetermination…”
  • Poyla (1954)
    • “…scientific thought as distinguished from everyday thought.”
slide3
BIAS

Building a Case

**no expectation of impartiality

Treatment and

Evaluation of Evidence

Motivated Bias

Philosophy

Logic

Statistics

Psychology

Impartial Evaluation

Unmotivated Bias

Hempel (1945)

Observed: A white shoe

Concluded: All ravens are black.

Logic: All observed non-black things are non-ravens (the Contrapositive)

Silly? All these insurgents are Muslim…

incarnations of confirmation bias
Incarnations of Confirmation Bias
  • Evidence interpretation
  • Evidence censoring
  • Restriction of alternative hypotheses
  • Seeking confirmatory evidence
  • Reification – over-estimating the salience of a taxonomy
  • Illusory Correlation
  • Primacy – becoming biased by the beginning of a stream of evidence, early hypothesis building
wasson 1966
Wasson(1966)
  • Four cards presented. Cards have a number on one side and a letter on the other.
  • Confirm or deny: All vowels have even numbers on the other side.

A

B

4

7

  • Most subjects (~90%) flip “A” and/or “4”
  • People seek to confirm the hypothesis, they do not seek countervailing evidence.
taylor and smyth 1860 s
Taylor and Smyth (1860’s)
  • Egyptologists and Numerologists, they discover “too strange” relationships in Pyramid dimensions.
    • (2 x base)/height = p
    • base/casing stone = 365
    • height * 109 = distance from earth to sun
    • density of the earth
    • period of the procession of the earth’s axis
    • mean temp of the earth’s surface
  • Conclusion: Space aliens directed the construction of the Pyramids
einstein and the expanding universe
Einstein and the Expanding Universe
  • Universe assumed static until mid-50’s
  • Expanding universe model could have been discovered by any post-Newton astronomer (S. Hawking, 1988)
  • Einstein actually had evidence of expansion as a by-product of General Relativity, but covered it with his now-infamous Cosmological Constant.
  • Called this the biggest mistake of his career.
type 1 error
Type 1 Error
  • recall P[type 1] = P[reject Ho|Ho] = a
  • Typical 1-tailed test runs on a = 0.025
  • In 40 independent tests, you EXPECT one false rejection
  • Sequential testing is a great temptation in simulation analysis
  • Ability to make STDERR arbitrarily small means that meaningful indifference zone needs to be determined a priori.
confirmation bias1
Confirmation Bias
  • Our leaders and customers have it
  • Our families and neighbors have it
  • We have it, but we can protect ourselves
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