Evidence and Proof

Where’s Your Proof?

Don’t believe everything you read or hear. One of the authors has a scar on his right leg because he failed to heed this advice. As a kid, he scraped his leg. A buddy informed him that dog saliva had healing powers, so he gladly let the family pooch lick away at the abrasion. That’s when the infection developed. He learned the hard way that dog drool has no antiseptic qualities whatsoever.

Unfortunately, the author’s childhood friend is not the only one handing out bad advice. It’s not uncommon to hear people support their claims with statements such as:

“I read somewhere that . . ..”

“Hey, trust me on this.”

“They couldn’t say it, if it weren’t true.”

“I know a guy, who knows a guy, who told him that . . ..”

When a person offers proof for a claim by asserting that there is proof for the claim, be wary. Just because someone claims to have seen “Bigfoot,” as some do (see www.bigfootencounters.com), doesn’t make it true. The same caution applies to tabloid gossip. For example, in 2017, actress Rebel Wilson won a $4.56 million defamation suit against an Australian publisher who branded her as a “serial liar.” The judge ruled that Bauer media had engaged in a “calculated, baseless and unjustifiable” attack that cost the actress movie roles (Ackerman, 2017, para. 1). Even legitimate news sources get their facts wrong—more often than one might think. For example, in a segment on CBS’ 60 Minutes that aired in 2004, Dan Rather relied on faked documents suggesting that George W. Bush shirked his duties while serving in the National Guard (Krauthammer, 2005; Memmott, 2004). Four producers were fired over the scandal and Rather left the show soon after. Since then, the incident has been called “a watershed moment in American TV journalism” (Anderson, 2015).

Prove It to Me

The problem is that we can’t always get our information first-hand. We must rely on media reports, government agencies, and social networks to find out what is going on in the world. But how can

“It’s a bedtime story. It doesn’t need corroboration.”

Figure 6.1 Budding skepticism

© Michael Maslin/Ihe New Yorker Collection/www.cartoonbank.com.

we know if such information is accurate? What tests might we use to assess the quality of evidence that is offered by others or that we might want to use in our own arguments? Learning to evaluate such information is not always easy. Indeed, Sadler (2004) noted that people of all ages “have difficulty in constructing well-substantiated arguments” (p. 516). With that in mind, this chapter examines the nature of evidence and how it is used, and abused, to support claims. In it, you’ll learn important tests for evaluating source credibility and evidence, including statistical proof.

Field Dependent and Field Invariant Proof

Some forms of evidence are field invariant, meaning that the standards for evaluating evidence can be understood by the general public, without special knowledge or training. A reasonable person standard is often applied in such cases. The reasonable person standard asks how an ordinary, reasonable person would judge the proof that is presented. The kinds of evidence found in Op-Ed pieces, offered by pundits on news shows, and included in position pieces in popular magazines fall into this category.

Other forms of evidence are field dependent, meaning that what constitutes acceptable proof is specific to a particular context, field, or discipline. In some specific fields, standards for collecting, presenting, and evaluating evidence are quite specific. In criminal law, for example, the exclusionary rule bars evidence obtained from an illegal search from being presented at trial. In journalism, reputable news organizations abide by a “two-source” rule, whereby two independent sources must corroborate a story before it can be published. In social science research, statistical significance (often at the p < .05 level) is commonly recognized as the threshold for proof. This means a researcher is 95 percent confident the results obtained are not due to chance. With the distinction between field invariant and field dependent standards for evidence in mind, we turn to some of the most basic field invariant tests of evidence next.

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