Using Bayes Factors to evaluate evidence for no effect: examples from the SIPS Project

Dienes, Zoltan, Coulton, Simon and Heather, Nick (2017) Using Bayes Factors to evaluate evidence for no effect: examples from the SIPS Project. Addiction. ISSN 0965-2140

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Abstract

Aims: To illustrate how Bayes Factors are important for determining the effectiveness of
interventions.
Method: We consider a case where inappropriate conclusions were publicly drawn based on
significance testing, namely the SIPS Project (Screening and Intervention Programme for Sensible
drinking), a pragmatic, cluster-randomized controlled trial in each of two healthcare settings and in
the criminal justice system. We showhow Bayes Factors can disambiguate the non-significant findings
from the SIPS Project and thus determine whether the findings represent evidence of absence or
absence of evidence. We show how to model the sort of effects that could be expected, and how to
check the robustness of the Bayes Factors.
Results: The findings from the three SIPS trials taken individually are largely uninformative but, when
data from these trials are combined, there is moderate evidence for a null hypothesis (H0) and thus
for a lack of effect of brief intervention compared with simple clinical feedback and an alcohol
information leaflet (B = 0.24, p = 0.43).
Conclusion: Scientists who find non-significant results should suspend judgment – unless they
calculate a Bayes Factor to indicate either that there is evidence for a null hypothesis (H0) over a (welljustified)
alternative hypothesis (H1), or else that more data are needed.

Item Type: Article
Keywords: Non-significance, Bayes Factors, Evidence of absence, Alcohol brief interventions, SIPS Project
Schools and Departments: School of Psychology > Psychology
Depositing User: Ellena Adams
Date Deposited: 17 Aug 2017 12:40
Last Modified: 24 Aug 2017 16:12
URI: http://sro.sussex.ac.uk/id/eprint/69861

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