On the interpretation of removable interactions: a survey of the field 33 years after Loftus

Eric-Jan Wagenmakers, Angelos-Miltiadis Krypotos, Amy H Criss, Geoff Iverson

Research output: Contribution to journalArticleAcademicpeer-review


In a classic 1978 Memory & Cognition article, Geoff Loftus explained why noncrossover interactions are removable. These removable interactions are tied to the scale of measurement for the dependent variable and therefore do not allow unambiguous conclusions about latent psychological processes. In the present article, we present concrete examples of how this insight helps prevent experimental psychologists from drawing incorrect conclusions about the effects of forgetting and aging. In addition, we extend the Loftus classification scheme for interactions to include those on the cusp between removable and nonremovable. Finally, we use various methods (i.e., a study of citation histories, a questionnaire for psychology students and faculty members, an analysis of statistical textbooks, and a review of articles published in the 2008 issue of Psychology and Aging) to show that experimental psychologists have remained generally unaware of the concept of removable interactions. We conclude that there is more to interactions in a 2 × 2 design than meets the eye.

Original languageEnglish
Pages (from-to)145-60
Number of pages16
JournalMemory & cognition
Issue number2
Publication statusPublished - Feb 2012
Externally publishedYes


  • Cognition Disorders
  • History, 20th Century
  • Humans
  • Mental Recall
  • Models, Psychological
  • Psychology, Experimental
  • Research Design


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