Please use this identifier to cite or link to this item: https://hdl.handle.net/10419/216533 
Year of Publication: 
2020
Series/Report no.: 
CESifo Working Paper No. 8137
Publisher: 
Center for Economic Studies and ifo Institute (CESifo), Munich
Abstract: 
Factorial designs are widely used for studying multiple treatments in one experiment. While "long" model t-tests provide valid inferences, "short" model t-tests (ignoring interactions) yield higher power if interactions are zero, but incorrect inferences otherwise. Of 27 factorial experiments published in top-5 journals (2007–2017), 19 use the short model. After including all interactions, over half their results lose significance. Modest local power improvements over the long model are possible, but with lower power for most values of the interaction. If interactions are not of interest, leaving the interaction cells empty yields valid inferences and global power improvements.
Subjects: 
randomized controlled trial
factorial designs
cross-cut designs
field experiments
JEL: 
C12
C18
C90
C93
Document Type: 
Working Paper
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