Published online 1 November 2011 | Nature 479, 15 (2011) | doi:10.1038/479015a

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Investigation claims dozens of social-psychology papers contain faked data.

Dutch psychologist Diederik Stapel. Persbureau van Eijndhoven

When colleagues called the work of Dutch psychologist Diederik Stapel too good to be true, they meant it as a compliment. But a preliminary investigative report (go.nature.com/tqmp5c) released on 31 October gives literal meaning to the phrase, detailing years of data manipulation and blatant fabrication by the prominent Tilburg University researcher.

"We have some 30 papers in peer-reviewed journals where we are actually sure that they are fake, and there are more to come," says Pim Levelt, chair of the committee that investigated Stapel's work at the university.

Stapel's eye-catching studies on aspects of social behaviour such as power and stereo­typing garnered wide press coverage. For example, in a recent Science paper (which the investigation has not identified as fraudulent), Stapel reported that untidy environments encouraged discrimination ( Science 332, 251–253; 2011).

"Somebody used the word 'wunderkind'," says Miles Hewstone, a social psychologist at the University of Oxford, UK. "He was one of the bright thrusting young stars of Dutch social psychology — highly published, highly cited, prize-winning, worked with lots of people, and very well thought of in the field."

In early September, however, Stapel was suspended from his position as dean of the Tilburg School of Social and Behavioral Sciences over suspicions of research fraud. In late August, three young researchers under Stapel's supervision had found irregularities in published data and notified the head of the social-psychology department, Marcel Zeelenberg. Levelt's committee joined up with sister committees at the universities of Groningen and Amsterdam, where Stapel has also worked, to produce the report. They are now combing through his publications and their supporting data, and interviewing collaborators, to map out the full extent of the misconduct.

Mistakes made

Stapel initially cooperated with the investi­gation by identifying fraudulent publications, but stopped because he said he was not physically or emotionally able to continue, says Levelt. In a statement, translated from Dutch, that is appended to the report, Stapel says: "I have made mistakes, but I was and am honestly concerned with the field of social psychology. I therefore regret the pain that I have caused others." Nature was unable to contact Stapel for comment.

The report does not identify specific papers that contain manipulated or fabricated data, pending the completion of the investigations. The investigators conclude, though, that Stapel acted alone. "The co-authors, and in particular the PhD students, were absolutely not involved, they really didn't know what was going on in this data fabrication," Levelt says.

Often, the report says, Stapel and a colleague or student came up with a hypothesis, and then designed an experiment to test it. Stapel took responsibility for collecting data through what he said was a network of contacts at other institutions, and several weeks later produced a fictitious data file for his colleague to write up into a paper. On other occasions, Stapel received co-authorship after producing data he claimed to have collected previously that exactly matched the needs of a colleague working on a particular study.

The data were also suspicious, the report says: effects were large; missing data and outliers were rare; and hypotheses were rarely refuted. Journals publishing Stapel's papers did not question the omission of details about where the data came from. "We see that the scientific checks and balances process has failed at several levels," Levelt says.

At a press conference, Tilburg University's rector, Philip Eijlander, said that he would pursue criminal prosecution of Stapel. The committee is also producing a list of tainted papers to guide co-authors and journal publishers in what will probably be a long list of retractions.

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Joris Lammers, a psychologist at Tilburg who did his PhD under Stapel's supervision, says he is "shocked" by the findings. Lammers says he worked independently of Stapel and collected all the data in his PhD himself — the report notes that his dissertation is not under suspicion. Several other former collaborators contacted by Nature declined to comment.

Hewstone, who has never worked with Stapel, had initially fretted that Stapel's fraudulent oeuvre would undermine other findings in the field of social psychology. While editing a new edition of a social-psychology textbook, however, Hewstone turned up no references to Stapel's work in 15 chapters, suggesting that Stapel's work was not as influential as he had thought. "I think the impact is going to be particularly devastating for the young people he worked with, but not for the field of social psychology as such," he says.

Science has published an Editorial Expression of Concern (http://go.nature.com/rLnV7Q) about Stapel's April paper on stereotypes and environment.