Tests of EvidenceTests of EvidencePart 2Part 2

the grounds of argumentthe grounds of argument

What is evidence?What is evidence?

Definition: “information, taken from material of fact or opinion, used to establish the probable truth of a claim (Rybacki & Rybacki, 2008, p. 100)

equivalent to the “grounds” in the Toulmin model

Forms of evidenceForms of evidence

personal experience examples facts, or conditions

that are empirically verifiable

authorities reports, studies,

official documents

physical artifacts testimony (quotations

from other sources) beliefs or premises

accepted by listeners statistics

Facts versus InferencesFacts versus Inferences

Two basic types of evidence• fact: empirically verifiable

phenomena– example: JFK was

assassinated in Dallas, TX• inference: anything requiring an

inference or judgment– example: cigarettes are more

dangerous than marijuana

Fact or inference?Fact or inference?

Which of the following is an empirically verifiable fact, which requires an inference?• More than 1 million

civilians have been killed in the Iraq war.

• All mammals give live birth.• Barry Bonds is the greatest

slugger of all time.• Hip hop music promotes

sexism, glorifies violence and embraces crass materialism.

• There are nine justices on the U.S. Supreme Court.

• The Great Pyramid of Giza was completed in 2560 B.C..

• Dark chocolate is good for you.

• Americans are the fattest people in the world.

RecencyRecency

is the evidence current, timely, up to date?

the advent of the 24 hr news cycle

recency is critical for traffic reports, election returns, stock market performance, weather forecasts,

in general, recency is more important in factual disputes than value disputes

On the Web: recency versus accuracy

RecencyRecency

Dewy Defeats Truman John McCain, Sept.

15, 2008:"Our economy, I think, is still -- the fundamentals of our economy are strong”

Recency: Is music piracy Recency: Is music piracy increasing or decreasing?increasing or decreasing?

May 12, 2006: the CEO of the Recording Industry Association of America says unauthorized song swapping has been “contained.”

Recency: Are abortions increasing Recency: Are abortions increasing or decreasing in the U.S.?or decreasing in the U.S.?

Legal elective abortions,Legal elective abortions,1972-2004, based on CDC1972-2004, based on CDCdatadata 1972:1972: 586,760 586,760 1980:1980: 1,297,6061,297,606 1985:1985: 1,328,5701,328,570 1990:1990: 1,429,2471,429,247 1995:1995: 1,210,8831,210,883 1997:1997: 1,186,0391,186,039 1999:1999: 861,789 861,789 20002000 857, 857,

475475 2001:2001: 853,485 853,485 2002:2002: 854,122 854,122 2003: 2003: 848, 163 848, 163 2004:2004: 839, 226 839, 226

The abortion rate in the U.S. The abortion rate in the U.S. is at its lowest rate in three is at its lowest rate in three decades.decades.

Current abortion rates are Current abortion rates are similar to those in 1975similar to those in 1975

Roe V. Wade decided was in Roe V. Wade decided was in 19731973

Recency: Are homicides in the Recency: Are homicides in the U.S. increasing or decreasing?U.S. increasing or decreasing?

Murder rates (per 100, 000 people) from Murder rates (per 100, 000 people) from 1990-20051990-2005•1990= 9.41990= 9.4•1991= 9.81991= 9.8•1992= 9.31992= 9.3•1993= 9.51993= 9.5•1994= 9.01994= 9.0•1995= 8.21995= 8.2•1996= 7.41996= 7.4•1997= 6.81997= 6.8•1998= 6.31998= 6.3•1999= 5.71999= 5.7•2000= 5.52000= 5.5•2001= 5.62001= 5.6•2002= 5.62002= 5.6•2003= 5.72003= 5.7•2004= 5.52004= 5.5•2005= 5.62005= 5.6

ConsistencyConsistency

Consistency: inconsistent or contradictory evidence is suspect• Iraq claimed it had no chemical

weapons, but Hussein previously used chemical weapons on his own people

• Cigarette manufacturers say they aren’t targeting children, but Philip Morris gave away thousands of free book covers to elementary schools with Philip Morris name on the cover

Internal versus external Internal versus external consistencyconsistency

Internal consistency: is the evidence consistent within itself (e.g., not self contradictory)?

example: A politician blames lower life expectancy in Cuba on communism, but doesn’t blame lower life expectancy in the U.S. on capitalism. (the U.S. ranks 45th in longevity, Cuba ranks 76th out of 221 countries)

Internal inconsistency:Bush on Internal inconsistency:Bush on wiretapswiretaps

Bush, April 2004: “Now, by the way, any time you hear the United States government talking about wiretap, it requires — a wiretap requires a court order. Nothing has changed, by the way. When we’re talking about chasing down terrorists, we’re talking about getting a court order before we do so.“

CNN, Jan 1, 2006: President Bush on Sunday defended his administration's use of wiretaps on U.S. citizens without a court order

Bush speech April 2004Bush speech April 2004

External consistencyExternal consistency

External consistency: does the evidence contradict other well-known, highly regarded evidence?

The Bush administration claimed “The jury is still out” on global warming, but the consensus of climatologists is that global warming is real.

External inconsistency: no gays, External inconsistency: no gays, no holocaustno holocaust

Iranian president Mahmoud Ahmadinejad, “In Iran we don't have homosexuals like in your country ... I don't know who's told you that we have this.” (Sept 25, 2007)

“They have invented a myth that Jews were massacred and place this above God, religions and the prophets…”

“The West has given more significance to the myth of the genocide of the Jews…” (Dec 14, 2005

Since the 1979 Since the 1979 revolution, homosexual revolution, homosexual acts are considered a acts are considered a capital crime in Iraq, capital crime in Iraq,

Correct interpretationCorrect interpretation

Correct interpretation: does the evidence really support the claim? Is the interpretation of the evidence correct?• Does sex education

increase teen promiscuity?• Does hiring more police

officers result in increased crime?

Unknowable StatisticsUnknowable Statistics Unknowable statistics: can

the phenomenon actually be counted, measured, are the numbers actually ascertainable?• Amount of illegal wagering in the

U.S.• Street value of illegal narcotics

trafficking While unknowable, some

estimates are still better than others

In his autobiography, In his autobiography, Wilt Chamberlain Wilt Chamberlain claimed he had slept claimed he had slept with over 20,000 with over 20,000 women!women!

Now Now thatthat is a scoring is a scoring record!record!

Unknowable statisticsUnknowable statistics March 2001: The INS estimated the

number of illegal aliens as 6 million. Scholars at Boston's Northeastern

University are now suggesting that the actual number might run as high as 13 million.

But the margin of error for the two estimates is 7 million, a number greater than the lower estimate itself!

March 2005: the PEW Hispanic Center estimates the undocumented population at 11.1 million including more than 6 million Mexicans.

March 2006 : The PEW Hispanic Center estimated there were 11.5 to 12 million undocumented immigrants.

Suppressed evidenceSuppressed evidence

Clinton’s convenient definition of “sexual relations”• Clinton: “I never had sexual

relations with that woman, Ms. Lewinsky, and I never asked anyone to lie about it.”

• Selectivity in ads quoting movie reviews, “the best feel-good movie of the summer,” “incredible special effects”

Suppressed evidenceSuppressed evidence

Merck and Vioxx risks: Since the recall of Vioxx in 2005, reports clearly show Merck knew as early as 2000 that Vioxx was killing arthritis patients.

Rather than doing something about it, Merck advertised the drug even more aggressively and engaged in a sophisticated campaign to hide the facts.

Conclusionary evidenceConclusionary evidence

Does the evidence contain a reason or rationale? (vs. conclusionary evidence)• A politician says: “I’m for

family values.”• “Smoking marijuana is

like holding a loaded gun to your head”