Correlation is not causation. Really?

"Correlation is not causation." Is that a true statement?

Edward R. Tufte says, "In fact, probably the shortest true statement that can be made about causality and correlation is "Empirically observed covariance is a necessary but not sufficient condition for causality."

Edward R. Tufte, "The Cognitive Style of PowerPoint: Pitching Out Corrupts Within," second edition, January 2006.

Knight's Reading List VII: July 2007

Knight’s Reading List VII: July 2007

Now that I’ve posted a reading list – see “Knight’s Reading List VI: June 2007” posted October 6, 2008 – I keep thinking how long ago I read those books. I feel the need to bring things closer to the present, to my present concerns and what I’ve been reading lately. In part, I think this may be helpful to those who read my other contributions to this blog, by letting them know more about my sources and inspirations.

In July 2007 I finished seven books. One of them had been “in the works” for a couple of years. Several were books about Al-Qaeda and the war in Iraq that I read while traveling in the Pacific Northwest. One was a mediocre historical novel set in Byzantium. This was, perhaps, an odd mix.

1 July: Michel de Montaigne, The Complete Essays of Montaigne, translated by Donald Frame. 1958. xxiii + 883 pages, including Index. I began reading this book in 2004 or early 2005, and started up again in July 2005. It took me an incredibly long time to read Montaigne, particularly as I enjoyed the essays greatly while reading them. The very richness of the essays was part of the problem I had; the classical allusions alone in some of the essays would give me material for reflection for days. Montaigne sends one scurrying off to Ovid’s Metamorphoses or Plutarch’s Lives, just to find out the meaning of some intriguing passage. There is in these essays a model for the would-be essayist, as well as reflections upon many affairs of interest. The man was his work, and the work is the man, and many will find Montaigne a good companion.

4 July: H. N. Turtletaub, Justinian. 1998. 511 pages. I began reading on 12 May 2008. I had read a number of books by Harry Turtledove, who writes alternate universe science fiction. He is workmanlike, but he is, if anything, too prolific. He spreads himself and his subject matter a bit thin at times. This historical novel was readable. Compared to Gore Vidal, however, Turtletaub is crude and amateurish at his task.

7 July: Lawrence Wright, The Looming Tower. 2006. 470 pages. I began reading it on 7 June 2008. This is a sinister book. It starts with Said Qutb, the Egyptian Islamist who visited the United States back in the 1950s, and went back to Cairo determined to reject the materialist ways of the West. It picks up with the Egyptian Dr. Ayman al-Zawahiri, and it comes, eventually, to Osama bin Laden himself. Part biography, part the history of a political movement, The Looming Tower doesn’t really explain why bin Laden became the head of Al Qaeda, or how it works, but it provides a lot of interesting insights into the revolutionary as capitalist manqué. I found that my concept of how the U.S. and the West could deal with the challenge of Islam challenged by the complex implications of Wright’s description of this multi-faceted movement.

13 July: Thomas Ricks, Fiasco. 2006. xiv + 482 pages, including Notes, Acknowledgements and Index. I began this one on 2 July 2007. As you can tell, Fiasco was a pretty fast read. Ricks is a reporter for the Washington Post, and he got to meet a lot of people, both in Washington and in Iraq. This is almost as high-level as Bob Woodward’s book, and gives one the same sense that a lot of the people charged with setting Iraq policy either didn’t know what they were doing, are were so encumbered by ideological blinders that they couldn’t bring themselves to do what needed to be done. I have the feeling that instant history of this sort will be supplanted, one day, by more thoughtful histories, which may, however, lose a lot of the atmosphere.

15 July: Bob Woodward, State of Denial. 2006. xiv + 560 pages, including Sources and Index. I began reading this on 4 July 2007. This is the third of Woodward’s books on the post 911 military actions of the U.S. Government. I intentionally read the first two – Bush at War and Plan of Attack before tackling State of Denial. My main reason for that choice was that I read in many reviews, favorable and unfavorable, from the right and from the left, that Woodward in this book “turned on” George W. Bush. (I finished Bush at War in October 2006, and Plan of Attack in November, so it took me a while to execute my program.) I don’t think Woodward changed at all. A lot of comments in the earlier books sounded like compliments as long as everything was going well; once the war turned sour, the same kinds of comments seemed uncomplimentary. Woodward’s technique is much like Ricks’, or any good reporter: He talks to a lot of people, records what they say, and then collates all of these interviews into a picture. That picture becomes grimmer and grimmer in the course of State of Denial, but I don’t think that Woodward was cooking the books. Like a good camera, he was presenting what he saw, and what he saw no longer made the White House look good.

19 July: Deborah J. Bennett, Logic Made Easy. 2004. 256 pages, including Notes, References and Index. I began this book on 4 July 2007. I’ve read quite a few books on logic, some more academic than others. I’m not sure where Deborah J. Bennett goes wrong, but this is less engaging than the ultimate dry logic book, W. V. Quine’s Elementary Logic. I don’t recommend this one. Not at all. Nope.

24 July: Rajiv Chandrasekaran, Imperial Life in the Emerald City. 2006. 320 pages. I started reading this on 10 July 2007. This is most enjoyable of the several Iraq books I read during this period. The “emerald city” of the title is a play on the “Green Zone” in Baghdad, and the resemblance to Oz is not accidental. An American outpost in a Muslim country where pork chops, bacon, ham, and hot dogs were served in huge quantities by the Muslim kitchen staff, the Green Zone had very little connection to the real world, and most of the people there treated it entirely as a way station en route to their next assignment in the States. Chandrasekaran, who, like Dexter Filkins of the New York Times, lived outside the Green Zone, tries to focus on the contrast between what was happening in the real Iraq, and the perceptions inside the hothouse atmosphere of the Pentagon’s Middle Eastern branch.

Knight's Reading List VI: June 2007

I haven't posted one of these in a while. I think it's about time to remind people that one of my primary activities is, and always has been, reading. I read a lot, I read widely, and some of what I read is pretty ephemeral - mystery novels, fantasies, and so on. But even a blind pig finds an acorn sometimes, and I sometimes come up with a good book.

In June 2007 I finished only six books, but a couple of them were extraordinarily good.

2 June: Stanley Portny, Project Management for Dummies. 2007. xviii + 366 pages. Begun on 4 May 2007. I like the "for Dummies" books, and doggone it! this was a pretty good one.

4 June: Nicholas Falletta, The Paradoxicon. 1983. xx + 230 pages. Begun on 2 June 2007. Interested in logic? Interested in strange, mind-twisting paradoxes? Interested in how paradoxes helped to develop the theory of logical thinking? Then this is a terrific book for you. It's a collection of paradoxes, with solutions when they are soluble. Of course it includes the riddle of "Who shaves the barber?", a paradox that changed modern thought. This is a lot of fun.

9 June: Gore Vidal, Lincoln. 1984. 657 pages. Begun on 12 May 2007. I read this book at the same time as the next one. They're both about Abraham Lincoln. They're both solidly based in good historical research. They were in some ways complementary, as when I used the maps in Kearns Goodwin's book to retrace the movements of Vidal's characters. But Vidal uses the power of fiction to fill in the gaps in the historical record, and leaves us a fascinating portrait of a great man, surrounded by rivals and enemies, and eventually brought down by them. They killed Lincoln, but they couldn't defeat him.

15 June: Doris Kearns Goodwin, Team of Rivals. 2005. xix + 916 pages. Begun 20 May 2007. This history is a welcome addition to the enormous volume of Lincolniana and Civil War histories. Goodwin's focus, like Vidal's, is on the personalities and interests of the men in Lincoln's cabinet, and the women who loved them. This book has some excellent illustrations, but Goodwin's descriptions of these personalities penetrate behind the paralytic photographs of the day.

23 June: John McPhee, Uncommon Carriers. 248 pages. Begun 18 June 2007. I note that I got through the 248 pages of McPhee's Uncommon Carriers in just six days. This is a collection of seven essays about transportation workers, and the systems within which they work. McPhee rides with a long-haul trucker, travels up the Illinois River on a tugboat pushing a raft of barges, and retraces Henry David Thoreau's canoe trip on the Concord and Merrimack rivers. McPhee is a terrific essayist. Gay Talese, in his introduction to a volume of The Best American Essays, mentions that McPhee came up as one of the "new journalists." I've read several of McPhee's books, including Annals of the Former World and The Founding Fish, and his technique is always the same: he finds someone who works in a field, and lives with that person, drawing out the individual life, the career it represents, and the subject matter upon which that career depends. Always worth reading, often surprising, sometimes touching.

30 June: Bill Bryson, The Lost Continent. 1989. 314 pages. Begun 20 June 2007. Bill Bryson spent twenty years living and working in England. Then he came back to the United States, and started to relearn his native land. In this book Bryson describes his travels from Iowa around the United States, visiting and sometimes revisiting various quarters of the country. He stays away from the coasts, preferring to travel the inland roads, through the small towns and rural areas of the country. This book invites comparison with William Least Heat Moon's Blue Highways, written fifteen or twenty years earlier.

The Absence of Evidence

Donald Rumsfeld made famous the saying that the absence of evidence is not evidence of absence. I don’t know anything about the origins of the saying, though I gather it was not original with Rumsfeld. The dictum itself may be unobjectionable, but Rumsfeld used it improperly and may have misled people thereby as to the meaning, and the limits, of this principle. I will explore here what the absence of evidence means.

The Absence of Elephants

You’re sitting at home on a Sunday afternoon, watching golf on television, which is to say that you are half-asleep, when the phone rings. The caller is one of your neighbors, and he says that there is an elephant in your front yard. You go to the window, you look out on the front yard, and there is no elephant there. You go back to the phone and say to your neighbor, “Good one. You made me look.” Then you hang up and go back to your golf.

I can divide your knowledge about elephants in your front yard into three states. In the first place, before the phone rings, you have no information. There is an absence of any evidence, as far as you know, regarding the presence or absence of elephants in your front yard. In fact, the possibility hasn’t even been raised. (It may be a general rule that a genuine absence of evidence coincides with a lack of interest in the question at hand.)

In the second state, after your neighbor calls, you have one piece of evidence: your neighbor’s testimony that an elephant is in your front yard. This may or may not seem likely to you, depending upon where you live and your prior experience. Under the principle of induction, if there has never been an elephant in your front yard before, it may seem unlikely that there is one at this time. However, the inductive problem, which indicates that any inductive conclusion can be overthrown by a single contrary example, implies that one should always be aware of the possibility of an instance contrary to one’s prior experience. One might call this keeping an “open mind.” Therefore, you go to the trouble of looking at the front yard, rather than dismissing your neighbor’s statement as a lame joke.

Finally, after you have looked at the front yard, you have another piece of evidence: your visual inspection of the yard shows that there are no elephants there. This evidence contradicts your neighbor’s statement, and (in your opinion) is conclusive. If you don’t see an elephant, there isn’t one. Your conclusion is that there is no elephant in your front yard.What I want to make clear with this example is that the absence of an elephant is not an absence of evidence concerning elephants. You have evidence concerning elephants, and this evidence is negative. That is, you have evidence of the absence of elephants. More generally, the absence of a phenomenon is not the same as the absence of evidence relevant to the existence of that phenomenon. Negative evidence is not the same as the absence of evidence.

The Case of Iraq’s Weapon’s Programs

Where Mr. Rumsfeld went wrong was in identifying an absence of material showing a particular outcome with an absence of evidence about that outcome. In fact, due to United Nations’ inspections, U.S. intelligence, and Iraqi reports, there was a lot of evidence about weapons of mass destruction in Iraq. On the one side, you had statements from Saddam Hussein and some of his underlings affirming that some weapons programs were in operation. (Whether they believed their own statements, or were running a bluff, is still uncertain.) On the other side, you had on-site inspections of places where such activities had taken place in the past, as well as places identified as suspicious by intelligence agencies, all of which showed that Iraq had complied with orders to terminate these programs.

In other words, the “elephant” in this case were weapons of mass destruction (WMD), and programs to manufacture and distribute them. Saddam Hussein himself, and certain intelligence sources claimed that there were active WMD in Iraq. On-site inspection, documentation, and a variety of intelligence sources contradicted those claims. Some photographic intelligence, much of which was (and always is) inherently ambiguous, supported the affirmative case. Other evidence supported the negative.

However you might wish to characterize the situation in Iraq in 2002 and 2003, an absence of evidence was not the problem. The problem was that the evidence available did not all point in one direction. It was not dispositive. It was clear that some of the weapons programs that had been in operation prior to 1991 were no longer functioning, at least not at the same scale or in the same places as they had been. It was clear that a lot of material had been destroyed under the sanctions regime, while there were no findings to show that it had been replaced. It also appeared that Saddam Hussein had the intention, or at least the wish, to develop WMD, if he ever had a free hand to do so.

In the end, by deciding to justify the invasion of Iraq on the existence of WMD, the Bush administration asserted that the affirmative evidence was more compelling than the negative evidence. A lot of people think they were wrong. To the extent that they dismissed the negative evidence as “an absence of evidence,” they were certainly wrong.

Conclusion

The absence of evidence means that one has no information about a subject. The absence of proof that something exists is not the same thing as the absence of evidence regarding its existence. Once one has evidence, one must evaluate it. Often, one needs to seek additional information to determine whether the initial evidence is credible or not. In many cases, the evidence is ambiguous or contradictory. Frequently, as in Iraq, the problem is not an absence of evidence: it is an inability rightly to assess the evidence one has.