The sort of error most commonly made by skeptics is going beyond the bounds of rational argument or beyond the available evidence in order to maintain a particular skeptical viewpoint. This includes failing to draw obvious conclusions from evidence and failure to obtain available evidence.
When conducting a skeptical investigation, it is not uncommon to find what appears to be a solution with only a modicum of effort. With the application of a little more effort, however, such solutions may quickly fall apart. I discovered this first hand in my investigation of the psychic detective claims of Scottsdale astrologer/psychic Jonathan Chris (Lippard 1988b). Chris claimed to have worked for the Tempe Police Department on the Christy Fornoff murder case in 1985. To check this claim, I did the obvious thing and contacted Lieutenant Steve Graheling, head of investigations for the TPD. Graheling told me that no psychics were used in the case. I might have stopped the investigation right there and simply concluded that Jonathan Chris was lying in his literature. But I would have been wrong. Further queries enabled me to discover that in fact, Tempe Police Sergeant Mike Palmer, the chief investigator on the Fornoff case, had consulted with Chris after all.
Something similar occurred in James Randi's investigation of psychic detective Dorothy Allison. Allison claimed to have given the name "Williams" to the Atlanta Police Department regarding the Atlanta child murders, for which Wayne Williams was eventually convicted. Randi (1982- 83) reports that, according to the APD's Sergeant Gundlach, Allison "had given them some 42 possible names for the murderer(s) but not the correct one." But when Marcello Truzzi (Hoebens with Truzzi 1985) checked with two Atlanta police officers whose names were given to him by Allison as witnesses, one of them did recall her having mentioned the name "Williams" (among others). Apparently the moral here is not to accept the word of police spokesmen regarding psychic detectives without independent corroborating evidence.
Another, more serious, example of not going far enough in a skeptical investigation may be found in the "News and Comment" section of the Spring 1980 Skeptical Inquirer in a brief article by Elie Shneour. Shneour's article was regarding a report in the October 23, 1979 issue of the tabloid Star regarding an experiment by "Professor Elizabeth Rauscher, a physicist of the Nuclear Division" at the Lawrence Radiation Laboratory (now the Lawrence Berkeley Laboratory) at the University of California at Berkeley. This experiment involved faith healer Olga Worrall successfully controlling the growth of bacteria.
According to Shneour, not only did no such experiments ever take place at the Lawrence Berkeley Lab (LBL), but there was no such person on the research staff or faculty or with any connection to the lab by the name of Elizabeth Rauscher. He stated that he obtained this information by contacting former colleagues at Berkeley. However, as I discovered while researching Mesa hypnotist Frank Baranowski's claim that a physicist named Elizabeth Rauscher was doing ghost research (Lippard 1988a), Shneour's second claim is false.
Rauscher was indeed on the staff at LBL at the time she conducted the experiment with Olga Worrall and bacteria (results published as Rauscher & Rubik 1979). Further, as she told me in a telephone conversation, she had written a letter of correction to the Skeptical Inquirer at the time, but it was never printed (Rauscher 1988). On the other hand, the work was not conducted at LBL, so Shneour was right about that part. But his failure to find Rauscher's existence and connection with the Lab is evidence of extremely poor research. All he needed to do to verify these facts was to examine a copy of what was then the most recent edition (14th, 1979) of American Men and Women of Science: Physical and Biological Sciences--Rauscher is listed there along with her affiliations. (For the record, Rauscher, who is active in parapsychology, indicates that she hasn't done "ghost research.")
Another case is CSICOP's handling of the "Mars effect" affair. In this case, a challenge to French "cosmobiologist" Michel Gauquelin resulted in the verification of his claim that correlations he found between the position of Mars and sports ability were not the result of factors such as births tending to occur at particular times of day. (For all the gory details of this mess, see Curry 1982 and Kammann 1982. Cherfas 1981 gives a brief summary.)
But what is by far the worst example of skeptical failure I have come across is a description of a March 18, 1988 debate between creationist Duane Gish of the Institute for Creation Research (ICR) and Ian Plimer, associate [sic] professor of geology at Newcastle University. The description of this debate which appeared in an article in the Australian Skeptics' publication The Skeptic, by Steve Roberts of the Canberra Skeptics and Skeptic editor Tim Mendham (Roberts & Mendham 1988) was filled with serious misrepresentations. I discovered this by viewing a videotape of the debate, which took place at the Clancy Theatre of the University of New South Wales in Sydney, Australia.
In the debate, Gish trotted out his standard anti- evolutionary arguments, and Plimer responded in extremely poor form with an unrelenting series of ad hominem attacks and a criticism of the worldwide flood theory. Plimer's behavior was so rude that the audience began shouting at him.
The first misrepresentation in the Roberts and Mendham (henceforth R&M) article involved Plimer's claim that Michael Denton, author of the book Evolution: A Theory in Crisis, had recanted his attack on evolution. Gish responded to this claim in his rebuttal, stating (as I have transcribed it from the videotape): "Dr. Denton did not deny or go back on anything he put in his book. This is what he did say: that if he were going to write a book on this subject that he'd take a different approach. The evidence that he discussed in here he said is subjective. ...But from the perspective now in genetic research he believes that possibly it's possible to objectively establish that [sic] if evolution is possible or not. And certainly from his present state of knowledge he believes it can be objectively proven that it's impossible." In R&M's description of this exchange, they state that Gish said Denton's remarks were that "if he were to rewrite [his book] he would take a different approach altogether, and that evolution was possibly now a provable reality given recent advances in technology." (p. 12) This misrepresentation was repeated in the July/August 1988 issue of the Creation/Evolution Newsletter (Anonymous 1988b).
Further misrepresentations are found in R&M's summary of Gish's presentation. They write that "Dr. Gish did make some truly remarkable admissions with respect to the body of beliefs held by creationists including himself, such as  that the universe is not necessarily very young,  that belief in the Biblical story of Noah and the Flood was suddenly optional and uncommon,  that the fossil record really is genuine and does not contain monkeys or human remains at an early era,  that data written and published by him was false and known by him to be false but had not been corrected,  that creation research institutes can do whatever they like with money acquired by them,  that there was a choice of various theories of creation including non-Christian ones. None of these revised policies were volunteered: they all came out under questioning." (p. 13, numbers added)
The quoted summary is full of errors. Gish's comments regarding points 1 and 6 were in response to questions from the audience. His comments regarding 2, 4, and 5 were in response to remarks made by Plimer in the debate. I am unable to ascertain what Gish said that R&M interpreted as point 3. Points 1, 4, and 6y are more-or-less true but slightly misleading, and points 2 and 5 are gross distortions.
1. In response to a question regarding the age of the universe and light from stars more than 10,000 light years away, Gish stated that he thought God created the light on its way to us but that this was not deception (because Gish interprets the book of Genesis to mean that God is telling us this "fact"). When the questioner asked about the recently- observed supernova which took place over 100,000 years ago, Gish stated that if that were established he would accept an old age for the universe.
2. Earlier in R&M's article Gish is quoted as admitting that "nobody really believed all that stuff about Noah and the Flood," (p. 12) which they describe so as to make it appear that Gish is denying belief in the biblical flood story. However, they have quoted Gish incorrectly and out- of-context. What Gish actually said (from the videotape) was: "Now, all of this funny stuff about Noah and the Ark and the Flood and all that, that's just a caricature. I don't know of any creation scientist who believes what [Plimer] says." He was responding to Plimer's claims about the number of animals that would have had to be on the Ark, the rate of continental drift, and so on, which he considered to be a caricature of creationist views about the flood.
3. As indicated above, I was unable to find any such admissions by Gish in the debate.
4. Plimer pointed out a number of errors (he called them "lies") in Gish's Have You Been Brainwashed? pamphlet, including the assertion that there are no Pre-Cambrian fossils. Gish responded that the pamphlet was 17 years old and that his statement was in accordance with the scientific views of the time. Plimer replied that he had just purchased a copy of the pamphlet outside the lecture hall.
5. Plimer noted the disappearance of a large quantity of money from the Australian Creation Science Foundation (CSF), implying that someone in the organization had absconded with the funds. Gish replied that the money had been invested and a dishonest person in the investment firm, not one of the creationists, had absconded with the funds.
6. In response to a question from an audience member regarding which version of creationism should be taught in schools, Gish said that none should. Instead, the creationist evidence against evolution should be presented. Which particular creationist story you believe is a matter of faith, not science.
Surprisingly, the ICR's account of this debate (Anonymous 1988a) is far more accurate than the Australian Skeptics' version, as well as being more charitable to the opposing side (e.g., the ICR account does not mention Plimer's invitation that Gish electrocute himself on bare wires to demonstrate that electricity is "mere" theory).
March 18, 1988: Duane Gish of the Institute for Creation Research (ICR) debates Australian skeptic Ian Plimer, professor of geology at the University of Newcastle. Plimer takes a very aggressive (ad hominem) stance, at one point offering Gish a chance to electrocute himself on bare wires since electricity, like evolution, is "only a theory." The ICR headlines their summary of the debate "Evolutionist Debater Descends to All-Time Low."
Winter (Australian) 1988: Steve Roberts and Tim Mendham publish an article (apparently primarily the writing of Roberts) in The Skeptic, the publication of the Australian Skeptics, describing the March 18 debate. The summary seriously misrepresents a number of Gish's statements, attributing to him such comments as "nobody really believed all that stuff about Noah and the Flood" and the claim that anti-evolution author Michael Denton now thinks evolution is "provable reality" (when Gish said quite the opposite). This latter piece of misinformation finds its way into the Creation/Evolution Newsletter (July/August 1988), under the headline "Is Michael Denton Anti-Evolution?"
Sometime in early 1989: I obtain a videotape of the debate and a copy of the Roberts and Mendham article, compare them and find discrepancies. I incorporate it into an article about errors by skeptics.
January 1990: My article, "Some Failures of Organized Skepticism," is published in The Arizona Skeptic. Copies are sent to the Australian Skeptics and the ICR (which also receives a copy of another article, "Dissension in the Ranks of the Institute for Creation Research"). The ICR responds with a thanks for the "objective analysis" in the former article and takes some issue with the latter. The Australian Skeptics do not respond.
June 1990: The (Australian) Creation Science Foundation (CSF) Prayer News publishes an article titled "American Skeptic Slams Australian Skeptics for 'Gross Distortions'."
July 1990: The CSF publication Creation Ex Nihilo (vol. 12, no. 3, p. 15) prints an article titled "US Skeptic claims Aussie Skeptics misrepresented Gish" which quotes liberally from "Some Failures of Organized Skepticism." Copies of both CSF articles are distributed at the annual convention of the Australian Skeptics.
July 17, 1990: Mark Plummer, president of the Victoria Branch of the Australian Skeptics and former CSICOP executive director, sends me copies of the two CSF publications along with a letter asking for a copy of my article and asking me "why [I] felt it was necessary for [my] article to be written." Copies of the letter are sent to James McGaha of the Tucson Skeptical Society (TUSKS) and Mike Stackpole of the Phoenix Skeptics. I do not receive my copy for several weeks because it is sent to an old address.
August 22, 1990: I reply to Plummer, stating that I saw misrepresentations and reported on them. I say that I probably erred in not sending a copy of my article to the Australian Skeptics in advance of publication.
September 28, 1990: Mark Plummer sends me a list of 12 questions as part of his "investigation" of my criticism of the Roberts & Mendham article. He asks such things as "From where did you obtain the videotape?", "What steps did you take to ensure that the videotape you viewed was an unedited version of the debate?", "Did you consult any appropriate experts prior to writing the article?", "Did you consult any experts on the traditions of debating American religious spokesmen in Australia?", and "What is your personal position on the creation/evolution issue?" I reply on October 7 to all of his questions. (The videotape was obtained from a Canadian skeptic who obtained it from Ian Plimer. I consulted no "experts" on the matter, since it was a simply case of a summary of a debate reporting something quite different from what actually occurred.)
Spring (Australian) 1990: Barry Williams, executive director of the Australian Skeptics, addresses my "Skeptical Failures" article in The Skeptic in response to a letter from CSF director Carl Wieland. He writes, "I am finally able to comment on the opinion expressed in the Arizona Skeptic, having at last seen a copy. The author of that opinion did indeed claim that our report of the Plimer/Gish debate was the 'worst example of skeptical failure' he had come across. In this, he appeared to be unable to distinguish between his own interpretation of a tape made of the debate and an on-the-spot news report which summarised the debate. Our report did contain some minor errors, which have been acknowledged in previous issues. As one of those who actually attended the debate, I disagree with the Arizona correspondent claims but perhaps one had to be sitting in the audience to savour the full flavour of what was said."
October 31, 1990: Thinking that Plummer may not be the right person to be communicating with and being very unclear on just what Barry Williams was trying to say about my article, I write a letter to the editor of The Skeptic. In my letter, I note that the CSF seemed to misrepresent my article as an attack on the Australian Skeptics when in fact it was a criticism of "a single article in a publication which generally produces excellent material." I reiterate some of my major criticisms and ask just where corrections to the errors in the summary had been published. The letter is neither published nor replied to (but see April 10, 1991, below).
October 1990: The CSF publishes A Response to Deception, a booklet responding to Barry Price's book, The Creation Science Controversy. The booklet includes serious allegations made against Price and Ian Plimer, and also includes a few sentences about my "Some Failures" article.
November 26, 1990: Plummer replies with an admission that there were some errors in the article (specifically mentioning only that the "Noah's Ark" comments were erroneous), but attacks me for "rushing into print" without "undertak[ing] the full research necessary to understand _why_ there were discrepancies." It seems that Roberts was working from longhand notes and the debate was "very lively and rowdy" and "at times hard to hear." So, Plummer concludes, I am guilty of wrongdoing but Roberts is not (Plummer calls my original article "sensationalist" and "akin to the National Enquirer"). Plummer also encloses several newsclippings designed to show me that in Australia, it is acceptable to bash religious people with ad hominem, insults, and ridicule. One clipping is a letter to the editor of a newspaper, one is an article from a trashy People-type magazine called The Picture, and the last is an article about a debate between Mark Plummer and a minister. Plummer's argument is undercut by comments in the Roberts & Mendham debate summary, which admits that "The adjudicator summed up by saying that, rather than a debate, the evening was more like a presentation by Dr. Gish and a series of derogatory replies by Dr. Plimer. He would award poor marks to both speakers, neither of whom had properly expounded his point of view as a science." (p. 13) The same page of the summary states that "Dr. Plimer's style of speaking excited comments and polarised the passions of quite a few people. Many Skeptics have said they were disappointed in his manner of presentation and his handling of the topic, preferring that he had presented purely the scientific evidence supporting evolution in a sombre and more scientifically respectable manner." (It goes on to rebut this via Plimer, who says that scientists have been doing that for years with little to show for it.)
November 30, 1990: Unconvinced by Plummer's arguments, I respond with an angry but reasoned reply, stating that The Skeptic still has an obligation to print a correction.
December 1990: Mike Stackpole's editorial piece, "Note of Importance," is published in The Arizona Skeptic. The article soundly rejects Mark Plummer's apparent opinion that skeptical groups, out of loyalty to "the cause," should not criticize each other.
December 17, 1990: Plummer responds to my letter with two sentences: "I acknowledge receipt of your letter of Nov 30th 1990. The information and rationalizations contained therein are sufficient for me to now report on your behavior." He then ceases further correspondence with me. I never receive any copy of Plummer's report or any comment on the conclusions of his "investigation."
December 31, 1990: I write to Barry Price, Ian Plimer, and the Australian Skeptics asking questions about the CSF's Response to Deception booklet. I receive replies from Price and Plimer, but not from the Australian Skeptics. For the next several months, I spend time corresponding with the CSF, Price, and Plimer about the various charges made by the CSF.
March 20, 1991: I complete a first draft of an article titled "How Not To Argue With Creationists" which criticizes Price and Plimer for various misrepresentations, and send copies to them for comment. Barry Price responds with an angry letter saying that I may end up being sued if I publish, that complaint will be made to my department head, and that a copy of my article has been forwarded to the Australian Skeptics. Meanwhile, Price himself was already being sued for defamation over remarks made in his book, The Creation Science Controversy.
April 10, 1991: I receive a letter, at long last, from Barry Williams (after Price sends him a copy of "How Not To Argue"). He says he sees no point in publishing my letter to The Skeptic because "I see no useful purpose being served by reopening a debate that took place more than three years ago" (despite the fact that he reopened the subject in the Spring 1990 issue of The Skeptic). He admits that there were factual errors in the article "which only became apparent to Steve Roberts the author, after he studied the tape some considerable time after the article had been published." As for The Skeptic's alleged publication of corrections, Williams notes that "We published three letters from people who had some comment to make on the debate, including one correcting an admitted error. This was from Ian Plimer's brother, taking issue with the description of Ian as a 'mild mannered Christian'." In other words, the only "error" corrected had nothing to do with my criticisms, contrary to the impression given by Williams' only published remarks about my article ("Spring (Australian) 1990," above). Williams went on to emphasize the cultural differences between the U.S. and Australia regarding creationism in an apparent attempt to dissuade me from publication of "How Not To Argue With Creationists."
April 22, 1991: I reply to Williams, reiterating The Skeptic's responsibility to correct its errors and noting my dismay at his misleading published comments about my article. I never receive a reply.
Summer 1991: NCSE Reports (formerly the Creation/Evolution Newsletter) prints my correction to "Is Michael Denton Anti-Evolution?" (under the headline "Michael Denton's Views Have Not Evolved After All"). In the editing process, my letter is altered to refer to Denton as a creationist (he isn't one). (The editor apologized for the mistake and a correction is forthcoming.)
July/August 1991: Wendy Grossman of the UK Skeptics writes in The Skeptic (British and Irish, not Australian) about the "fooferaw (US term for kerfuffle)" between the Australian Skeptics and the Phoenix Skeptics. Although she admits that "I wasn't there, and I haven't read all the letters, and I haven't seen the videotape" she doesn't "let that disqualify me from making a point of my own." She agrees that skepticism involves inquiry, a passion for truth, and no stifling of dissent, but criticizes me for sending my article to the ICR. She states that had she been in my place, she "would have mailed my criticisms to the Australian Skeptic for inclusion in the next issue or to give them a chance to publish a correction." While I don't agree that the article should not have been sent to the ICR, I do agree that the Australian Skeptics should have been given a chance to correct the error before I did so (but as the timeline above shows, the Australian Skeptics did nothing in the five months before the creationists published anything regarding my article). I submit a brief letter of response noting my opinions.
November 1991: "How Not To Argue With Creationists" is accepted and slated for publication in the next issue of Creation/Evolution.
[Added 5 August 2009: And the further "How Not to Respond to Criticism" has been available online since 1993.]