A letter submitted to the editor of a national newsmagazine was written and signed by a Dr. Shirley Martin who, in th...

smilde11 September 2, 2018

PT 14, S2, Q25

When I read answer E, I understand how the flaws are parallel, however doesn't it require the assumption that there is no male professor by the name Shirley? Similar to the boy named Sue example used in the lessons. Or am I totally missing something else? I ran out of time on this one because I kept reading the passage over and over to understand the flaw before moving on to the answer choices, but had I gone over the answers, I definitely would have gotten this. Thanks for your help!

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Max-Youngquist September 2, 2018

@smilde11 think about it this way: we can combine the two probabilities together to get the following:

Probability professor is male: 95%
Probability Shirley is male: unknown % (we'll use the variable PSM)

So the probability that this particular professor named Shirley is a male is: .95 x PSM.

So note that the only way this formula could equal .95 is if 100% of Shirleys were MALE. In other words, if there's even one FEMALE named Shirley, then the conclusion is invalid. So it doesn't even matter if someone answering this question decides whether Shirley is "typically" a male or female name; as long as you recognize that there is at least one female Shirley, then the conclusion is flawed.

I hope that helps!

Anna20 February 10, 2021

Hi Team - thanks very much for the above. I'm not sure I understand the flaw in this argument? I picked D as the answer because of the similarity in language, grateful if you could please explain why this and the other answer choices are incorrect and why E is actually correct? Thank you!

Emil-Kunkin June 23, 2024

The flaw in the argument is that the author assumes that since 95 percent of a group has characteristic X, that each individual in the group has a 95% chance of being X, even if there is disconfirming evidence. In both cases, the group as a whole plans overwhelmingly in one direction. However, there is evidence that the individual in question is a member of the minority. While there are some flying mammals (well one really, I cant think of any besides bats), most flying things are birds. Likewise, while Shirley can be a mans name, it is far more common that a Shirley is a woman. D doesnt commit this same flaw, it applies what is true of one group to be true of another group.