The fraudulent research practices of social
psychologist Diederik Stapel
The scientific fraud committed by Diederik Stapel, which came to light in Tilburg in early September 2011,
sent shock waves across the academic world in the Netherlands and internationally. Ultimately, trust forms
the basis of all scientific collaboration. If, as in the case of Mr Stapel, there is a serious breach of that trust,
the very foundations of science are undermined.
Is science’s purported self-cleansing ability really up to the challenge of dealing with such a serious
infringement of scientific integrity? From the outset, the Rector Magnificus of Tilburg University decided
to opt for full disclosure. He established a committee of enquiry, the Levelt Committee, charged with
establishing the nature and extent of the fraud and examining the research culture that had allowed this
fraud to persist over such a lengthy period. This picture could not be complete without involving Mr
Stapel’s previous places of employment within the scope of the investigation: the University of Amsterdam
(UvA), where he studied from 1993 until 1999 and was awarded his doctorate in 1997, and the University
of Groningen, where he held the position of full professor from 2000 until 2006. In mutual consultation
between the three universities, the Drenth Committee was established in Amsterdam and the Noort
Committee in Groningen. In this final report, the three Committees present their findings jointly.
When the fraud was first discovered, limiting the harm it caused for the victims was a matter of urgency.
This was particularly the case for Mr Stapel’s former PhD students and postdoctoral researchers, whose
publications were suddenly becoming worthless. In an interim report, published in late October 2011,
the Committees reported on the extent of this harm and also concluded that none of these authors or coauthors
had been accessories in Mr Stapel’s fraud. The report also outlined the nature of the fraud and of the
research culture in which it had occurred. This interim report was made public immediately.
However, the Committees were of the opinion that the main bulk of the work had not yet even started. The
case involved an extensive body of scientific work that was now tainted. In a well-functioning scientific
world, the task now was to separate the wheat from the chaff. Journal publications can often leave traces
that reach far into and even beyond scientific disciplines. The self-cleansing character of science calls for
fraudulent publications to be withdrawn and no longer to proliferate within the literature. In addition, based
on their initial impressions, the Committees believed that there were other serious issues within Mr Stapel’s
publications, even if they were not fraudulent. These issues are referred to in this report as ‘sloppy science’:
a failure to meet normal standards of methodology. This brought into the spotlight a research culture in
which this sloppy science, alongside out-and-out fraud, was able to remain undetected for so long. This also
necessitated a scientific self-cleansing operation.
It is to the credit of the three universities involved that they gave the Committees a free hand to analyse
all of Mr Stapel’s publications. In this process, cooperation was requested from the co-authors. They all
offered this without exception, by submitting research materials and data and in many cases by informing
us in interviews of the circumstances of their research. In addition, all three universities placed statisticians
at the disposal of the Committees in order to subject all of Mr Stapel’s publications to a rigorous analysis.
Obviously, this was a labour-intensive and expensive operation. As far as we are aware, this was the
first time ever that the whole of a fraudster’s body of scientific work had been scrutinized in this way.
Committees usually restrict themselves to an investigation of articles reported to be suspect or to a small
random sample. In many cases, this can indeed deliver proof of fraud. However, there is always a greater
interest at stake. The scientific literature must be cleansed of everything that is fraudulent, especially if it
involves the work of a leading academic. Of course, this is of particular importance in medicine, where
fraudulent publications can have harmful consequences for large groups of patients. But it is also the
case for less applied sciences, including social psychology. No more time and money must be wasted on
replications or meta-analyses of fabricated data. Researchers’ and especially students’ too rosy view of the
discipline, caused by such publications, should be corrected. In this particular case, journals, reviewers,
assessment committees and graduate schools must learn a methodological lesson: it appears that too much
can go wrong in the discipline’s critical functions.
Nevertheless, the most important reason for seeking completeness in cleansing the scientific record is that
science itself has a particular claim to the finding of truth. This is a cumulative process, characterized in
empirical science, and especially in psychology, as an empirical cycle, a continuous process of alternating
between the development of theories and empirical testing. A theory has a provisional claim on truth/
validity, as long as it has not been empirically disproven. Ultimately, cumulative evidence can result in
consensus within the peer community on a theory’s validity. This fundamental cumulative process is
seriously disrupted by interference from fraudulent data and findings based on questionable methodology.
The scientific researchers and institutions involved are duty bound to call a halt to this disruption.
Sadly, some of the Committees’ findings are echoed in the recent open e-mail on the current situation in
social psychology published by Nobel prizewinner Daniel Kahneman: ‘Your field is now the poster child
for doubts about the integrity of psychological research. Your problem is not with a few people who have
actively challenged the validity of some priming results. It is with the much larger population of colleagues
who in the past accepted your surprising results as facts when they were published. These people have
now attached a question mark to the field, and it is your responsibility to remove it.’ Kahneman can see ‘a
train wreck looming. I expect the first victims to be young people on the job market.’ If this report and the
wrongdoings it highlights can contribute to this cleansing process, the Stapel fraud may still have a positive
impact, alongside all of the damage and personal harm it has caused.
The Committees would like to express their gratitude to the three University Rectors for their actual and
moral support in their work. They would also like to thank the devoted statisticians who conducted their
painstaking analyses often under extreme pressure. Without the open discussions with co-authors and with
others involved, the in-depth analysis included in this report would not have been possible. Especially for
the victims of this fraud, these discussions were often fraught with emotion. Therefore, their contributions
to the work of our Committees deserve a special mention of gratitude. Finally, the Committees offer
their thanks to their excellent executive secretaries, who have organized the work of the Committees for
more than one year and are responsible for much of this report. The names of all of the people who have
supported the work of the Committees in this way are listed in Appendix 1 of this final report.
This final report now brings the work of the Committees to its conclusion.
Willem J.M. Levelt, Chair of the Coordinating Committee