September 18th, 2014 (Permalink)

Letter to the Editor

Letters to the editors of magazines and newspapers often provide brief arguments that are good for exercising your skill in understanding reasoning, and even occasionally spotting a fallacy. So, brush up on your logical skills if you need to―see the Lessons, below―and let's get started. The following letter is taken from the Sunday book review section of The New York Times. First, read through the entire letter―see Source 1, below, it's short―or read the following excerpt, which is most of it:

William Deresiewicz argues in his new book, “Excellent Sheep”…that Ivy League schools graduate narrow, dissatisfied and purposeless students. But his anecdotal accounts do not jibe with my 20 years of experience on the faculty of Stanford University, where the majority of undergrads are happy, passionate and thriving. These amazingly talented and diverse students are working side by side with our faculty to reinvent the world. … Based on his unduly negative outlook, I would guess that Deresiewicz feels he was unfairly denied tenure at Yale. But it is time for him to stop whingeing and get back to the teaching and mentoring that he excels at and loves.―Ben Barres

Just what is Barres trying to argue? As I mentioned, this is a letter to the editor of the book review section of The N. Y. Times, and Barres is responding to a review of the book Excellent Sheep. However, unlike many such letters to the book review, he is not writing to defend the author of the book from criticism. Rather, he is criticizing what he takes to be the author's thesis which, according to the letter's first sentence, is: "Ivy League schools graduate narrow, dissatisfied and purposeless students."

Now, I haven't read Excellent Sheep, so I don't know whether this is an accurate characterization of the book's claims. I also don't know whether Barres has read it or is relying on the review's characterization of it. In any case, there is a possibility that the letter is criticizing an inaccurate version of the book's thesis, in which case it's attacking a straw man.

After stating what he takes to be the book's portrayal of Ivy League students, Barres proceeds in the next two sentences to testify against it based on his own experience as a faculty member of Stanford University. Stanford is not, strictly speaking, a member of the Ivy League, though it is the sort of elite university that Deresiewicz appears to be dealing with in his book. The problem with Barres' testimony is that he is just one person at one elite institution: his testimony is some evidence against the book's claims, but quite weak evidence. Barres' experiences may well be based on an unrepresentative sample of students at elite institutions.

Besides, Barres is just one guy. One person at one school is the smallest sample you can have, so it would be quite a hasty generalization to conclude that the book is wrong based on such a small, possibly biased sample. Barres refers to Deresiewicz' "anecdotal accounts", so perhaps he intends to place his own anecdotal account against Deresiewicz. Given my ignorance of the book, this is another possibility I can't verify or dismiss.

Finally, in the last two sentences of the letter, Barres turns to an ad hominem attack on the author of the book. He engages in some amateur psychoanalysis, suggesting that Deresiewicz is complaining bitterly―"whingeing"―just because he was denied tenure at Yale. This, of course, is also a sneaky way to put Deresiewicz down by alluding to the tenure denial. If turnabout were fair play, one might suggest that Barres is bitter because Yale really is an Ivy League school and he's just envious of Deresiewicz. Given that it seems possible that an untenured professor at Yale, or even at Stanford, could write a good book about Ivy League education, this is a fallacious personal attack.

To sum up, there is one glaring fallacy committed by the letter, namely, the ad hominem at the end. More importantly, the letter's argument is a very weak, anecdotal one at best.


  1. Ben Barres, "Poor Little Lambs", The New York Times Sunday Book Review, 9/5/2014
  2. Dwight Garner, "The Lower Ambitions of Higher Education", The New York Times, 8/12/2014. Another review from The Times, which also claims that Deresiewicz was denied tenure.
  3. Anthony Grafton, "The Enclosure of the American Mind", The New York Times Sunday Book Review, 8/22/2014

10 Brief Lessons in Logic: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10


September 12th, 2014 (Permalink)

The Puzzle of the Four Conspirators

A little over a year ago the police consulted with you about a bank-robbing gang, and thanks to your help the gangsters are doing hard time. Now, a police informant has revealed that another gang is planning a heist. Each robber will have one of four specific jobs: the Brains, the Muscle, the Safecracker, and the Wheelman. Having managed to plant bugs in the room where the four criminals are planning the heist, the police overheard the gang discussing the upcoming job:

  1. Artie was heard saying that Danny was the smartest and so ought to be the Brains.
  2. Benjy argued at length that they ought to hit an armored car instead of a bank.
  3. Charlie loudly insisted that Artie was not strong enough to be the Muscle.
  4. Danny claimed that Benjy was not skilled enough to be the Safecracker.

Later, after the decisions were made, the police heard all but one of the crooks complaining that their recommendations had not been followed. Fittingly, the only member of the gang whose advice had been taken was the man who became the Brains. Also, the conspirators had definitely decided to hit either a bank or an armored car, but the police couldn't tell which.

Can you help the police by determining what job each conspirator has been assigned in the heist, and whether they have decided to rob a bank or an armored car?


September 9th, 2014 (Permalink)

New Book: The Organized Mind

Psychologist Daniel J. Levitin, author of a couple of books on music, has a new book: The Organized Mind: Thinking Straight in the Age of Information Overload. Of course, it's the "thinking straight" part that is most relevant for us. Levitin was a student of the late Amos Tversky (p. xxii), so he should know a lot about how cognitive biases and illusions interfere with straight thinking.

September 5th, 2014 (Permalink)

One "myth" that's not quite dead yet

A few years ago I wrote about a shocking statistical claim: "Up to 300,000 girls between 11 and 17 are lured into the U.S. sex industry annually…." At the time, I searched but failed to discover where this claim originated, or what evidence supported it. Instead, I did a "back-of-the-envelope calculation" (BOTEC) to test its plausibility, since I found the number intuitively implausible―see the Resource, below, for the results. According to an article in The Village Voice―see Source 1, below―that appeared a few months after my original entry but which I just recently discovered:

The "100,000 to 300,000"…―the same number that's found its way into dozens of reputable newspapers―came from two University of Pennsylvania professors, Richard J. Estes and Neil Alan Weiner.

Presumably, the "300,000" in the claim that I wrote about is the high end of this estimated range. Unfortunately, the Voice article doesn't explain exactly where the estimate is supposed to come from, though they do quote from a 2001 report authored by Estes and Weiner (E&W)―see Source 2, below. However, though I haven't read the entire report―it's over 200 pages―I don't see any indication that the 100k-300k estimate is due to E&W or the report's own estimate. Instead, the report gives low, medium, and high estimates of 244,181, 286,506, and 325,575, respectively―for those of you playing along at home, these numbers are over-precise. However, if you were to state them as a range from low to high, you'd probably come up with 250k-350k, rather than 100k-300k. For this reason, it seems unlikely that they are the source for the latter estimate.

The Voice article makes a big deal about the fact that E&W's estimate was of children "at risk" for commercial sexual exploitation rather than those actually being so exploited, which is true but beside the point. If the 100k-300k estimate did not come from E&W, then a clearer example of ignoratio elenchi would be hard to find.

So, where did the 100k-300k estimate come from? Of course, I can't be certain, but the 2001 report says the following:

…[T]he first World Congress Against the Commercial Sexual Exploitation of Children …confirmed that large numbers of prostituted children are to be found in rich countries, including in the U.S. for which the "End Child Prostitution, Child Pornography, and the Trafficking of Children for Sexual Exploitation"…estimated their numbers to be between 100,000 and 300,000…. (P. 4)

The passage cites a 1996 report (p. 215) which I have not been able to find online or elsewhere―if you should happen to know where I can find a copy of this report I would be obliged if you let me know. As a result, it's impossible to check the report's methodology for arriving at this estimate, though the wording indicates that this is not supposed to be an estimate of "at risk" children, but of those actually exploited. If so, and if this is the actual source of the original estimate, then the Voice criticism misses the mark. However, the same report quoted above goes on to say:

One of the principal objectives of the present study was to place some reasonable though tentative parameters around the magnitude of the contemporary CSEC [Commercial Sexual Exploitation of Children] phenomenon in the United States. Previous estimates of the number of such cases ranged from a low of 300,000…to a high of as many as 1,000,000 cases…. Neither estimate, though, was based on empirically-derived evidence, and both assertions have been widely criticized as lacking scientific merit. Thus, the present investigation was initiated in the absence of reliable baseline data against which our own findings could even be compared…. (P. 143)

It's odd that this passage claims that 300k is a "low" estimate given that the previous passage gives a range starting at 100k, and both passages cite the same 1996 report. However, the authors indicate that the earlier estimate was not "empirically-derived" nor such that they were willing to rely on it for baseline data.

Also, it should be noted that none of this affects my earlier critique of the claim that "up to 300,000 girls between 11 and 17 are lured into the U.S. sex industry annually". This claim picks the upper end of the estimated range in order to use the larger, more shocking, number. Moreover, the 1996 estimate, as described by E&W, does not say that this number is added "annually", so presumably it is supposed to be the absolute number of exploited children. This is still an implausible claim, but less so.


  1. Martin Cizmar, Ellis Conklin & Kristen Hinman, "Real Men Get Their Facts Straight", The Village Voice, 6/29/2011
  2. Richard J. Estes & Neil Alan Weiner, "The Commercial Sexual Exploitation of Children in the U.S., Canada and Mexico", 2001 (PDF)

Resource: BOTEC, 2/6/2011

Via: Christina Hoff Sommers, "5 Feminist Myths That Will Not Die", Time, 9/2/2014, Myth 2. Sommers seems to have made the mistake of taking this "myth" uncritically from The Village Voice.

August 30th, 2014 (Permalink)

New Book: Standard Deviations

Michael Shermer's latest "Skeptic" column in Scientific American―see Source 2, below―is not a review exactly, but is at least based on a new book by Gary Smith, Standard Deviations: Flawed Assumptions, Tortured Data, and Other Ways to Lie with Statistics.

In the column, Shermer discusses "survivor bias", which I think is the same thing as "survivorship bias", though I'm not certain for a reason I'll explain later. This caught my attention because the first story told in Jordan Ellenberg's new book, How Not to be Wrong, is an illustration of survivorship bias. I've mentioned Ellenberg's book here previously―see Resource 2, below― and you can read the first part via the "Look inside" feature at Amazon, if you're interested.

After the first two paragraphs, Shermer's article is a description of the same statistical phenomenon that Ellenberg discusses. I'll leave it to you to read either Shermer's short account or the longer one given by Ellenberg. However, I'm puzzled by Shermer's first two paragraphs where he tells two similar anecdotes, of which I'll quote the first:

When I purchased my latest vehicle, I was astonished to get the license plate 6NWL485. What are the chances that I would get that particular configuration? Before I received it, the odds were one in 175,760,000. (The number of letters in the alphabet to the power of the number of letters on the plate times the number of digits from 1 to 10 to the power of the number of digits on the plate: 263 × 104.) After the fact, however, the probability is one. This is what Pomona College economist Gary Smith calls the “survivor bias,” which he highlights as one of many statistically related cognitive biases in his deeply insightful book Standard Deviations….

By the way, I've fixed two typos that are in the online version of this article―they're not in the print version―namely, the exponents are not shown in superscript, so that it appears that 263 × 104 = 175,760,000. Not even close.

Anyway, here's what puzzles me: both of the little stories that Shermer tells seem to be related to Stephen Law's "lottery fallacy", which I've discussed in the context of the fine-tuning argument and the multiverse theory―see Resource 1, below. In other words, Shermer claims to have been "astonished" at the license plate he received because it was so unlikely that he would receive that particular one. Of course, he wasn't really astonished, because it would have been just as unlikely for him to have received any other plate. I won't recapitulate the whole argument here, which you can read in the Resource and other sources and resources linked to it.

However, what do these anecdotes have to do with survivorship bias? I suppose that one can stretch the notion of "survivors" to include the numbers that come up in a lottery, but the point of survivorship bias is that we either forget, ignore, or sometimes aren't even aware of those that don't survive. In the case of the lottery fallacy, it's because we're acutely aware of just how many other numbers were not picked that we're "astonished" at our luck.

So, these don't seem to me to be related phenomena, but perhaps Smith explains what's going on here in his book more clearly than Shermer does in his short column.


  1. Jordan Ellenberg, How Not to be Wrong: The Power of Mathematical Thinking (2014), pp. 3-9
  2. Michael Shermer, "How the Survivor Bias Distorts Reality", Scientific American, 8/19/2014


  1. The Lottery Fallacy, 7/9/2011
  2. New Book: How Not to be Wrong, 6/3/2014

August 27th, 2014 (Permalink)

New Edition: Logic Gallery (Third Edition, Enlarged)

David Marans' Logic Gallery is now available in an actual paper edition―imagine that: a whole book printed on paper! Not only that, but your purchase of the paperback edition will benefit the charitable organization Doctors Without Borders. Of course, there's still a free electronic version available. See the Sources, below, for links to both versions.

The Logic Gallery is a chronological collection of pictures of famous logicians, together with short biographical information, and interesting quotes. In fact, I intend to mine it for quotes about logic and fallacies.

Sources: David Marans, Logic Gallery: Ancient Greece to the 21st Century, Third Edition, Enlarged (2014):

Resource: New Book, 8/26/2010

The Fallacy Files 2: Blurb Watch
August 22nd, 2014 (Permalink)


Here's something I've never noticed before. A newspaper ad for the new movie Sin City: A Dame to Kill For―a sequel to Sin City, of course―has a total of ten blurbs. The ad seems to be trying to impress the reader with the sheer number of quotes.

Currently, the movie has a "rotten" 43% rating on Rotten Tomatoes' "Tomatometer", an average of many reviews. Metacritic's similar "Metascore" is "44", which is described as "Mixed or Average Reviews", but is only a few points above the "Generally Unfavorable Reviews" category. As a result, there were probably few favorable reviews to quote, so where did the ad writer find so many good blurbs?

Three of them are attributed to Debbie Lynn Elias of the Culver City Observer, but I haven't been able to find a review on the newspaper's website, so I can't check them. However, two are credited to Joel Amos of the Movie Fanatic website: "STUNNING." and "JOSH BROLIN IS BRILLIANT." So, the ad writer found so many quotes partly by drawing multiple ones from the same critic. In fact, there are only six different sources for the ten blurbs.

Surprisingly, if you check Amos' review of the movie―see Source 3, below―you'll find that Amos gave the movie only two stars out of a possible five, corresponding to a 40% rating, which is in line with the Rotten Tomatoes and Metacritic averages. Not only that, but the words "stunning" and "brilliant" are nowhere to be found in the review. So, where did those words come from?

I can only speculate, but Amos did use the word "stunning" in a different article―see Source 2, below―which was a short introduction to a "featurette" on the movie, of which he writes:

The visual style is what made Sin City such a marvel and judging by what we’ve seen so far of the second film, it is even more mesmerizing on the eyes. Watching this behind-the-scenes featurette, viewers get a fantastic look at how Rodriguez and Miller [the directors] achieved this stunning look…

Presumably, this was written prior to Amos actually seeing the entire movie, which must have turned out to be not so stunning. But what about the word "brilliant" as applied to Josh Brolin?

I found an interview with Brolin conducted by Amos two years ago for Men in Black 3, the title of which refers to Brolin's "brilliance"―see Source 1, below. Could this really be what the ad is referring to? If so, this is a stunning and brilliant display of blurbing prowess!


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