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Following research into the statistical veracity of the data used in publications by Jens Förster, four dissertations he supervised have been reviewed.

In June 2015, three independent statistical experts found strong statistical evidence of ‘low veracity’ in the results of eight publications by social psychologist Jens Förster. The UvA subsequently notified the respective journals and requested a retraction or expression of concern. The UvA also announced that the dissertations supervised by Jens Förster would be investigated. The study into these four theses has now been concluded.

The authors Letty Koopman, Frans J. Oort and Chris A.J. Klaassen found no evidence of low veracity of the reported results in three of the four investigated theses. They did, however, conclude that two chapters in one thesis show various peculiarities in their results. These chapters have been published as Gillebaart et al. (2012). The authors conclude that ‘Gillebaart et al. (2012) shows strong evidence of low scientific veracity of its results. However, since the underlying data was collected under the responsibility of Förster, we stress that his co-authors should not be blamed for this, in our opinion.’

The full report, Evaluating the Scientific Veracity of PhD Theses Written under Supervision of Prof. Dr. Jens Förster, can be read here.

Following receipt of the report, the Executive Board of the University of Amsterdam has requested the editors of the Journal of Experimental Psychology to retract the article by Gillebaart et al. (2012).

In its request, the Executive Board writes that ‘The number of peculiarities in the results as reported by the investigators - the inexplicable linearity, the extreme effect sizes, and the lack of reliability and interchangeability on which the conclusions hinge, in combination with lack of clarity on the source of the data - leads the Executive Board to the decision to ask for retraction”.

Acting upon the recommendation by the independent statistical experts, the Doctorate Board of the University of Amsterdam concludes that the thesis containing the two chapters itself is not in question. The experts conclude that the data used by Gillebaart were collected and processed by Jens Förster or by one or more others under his responsibility. Only after processing the data, Jens Förster provided the data to Gillebaart, on the basis of which she wrote an article. Hence Gillebaart cannot be blamed for the data collection and data processing.

Gillebaart, M., Förster, J. & Rotteveel, M. (2012): Mere Exposure Revisited: The Influence of Growth Versus Security Cues on Evaluations of Novel and Familiar Stimuli. Journal of Experimental Psychology: General, 141, 699-714.