Omission bias in vaccination decisions: Where's the "omission"? Where's the "bias"?

Terry Connolly, Reb Jochen

Research output: Contribution to journalArticlepeer-review

103 Scopus citations


Several studies have reported that parents are often reluctant to vaccinate their own or other people's children, even when the balance of health risks and benefits clearly favors vaccination. This reluctance has been interpreted as a manifestation of "omission bias", a general tendency to prefer inactive to active options even when inaction leads to worse outcomes or greater risks. The research raises significant public health concerns as well as worries about human decision biases in general. In this paper we argue that existing research on vaccination decisions has not convincingly demonstrated any general reluctance to vaccinate nor has it made the case that such a tendency, if found, would constitute a bias. We identify several conceptual and methodological issues that, we argue, cloud interpretation of earlier studies. In a new questionnaire-based study (Experiment 1) we examined the vaccination decisions of undergraduate students (N = 103) and non-student adults (N = 192). In both groups a clear majority chose to vaccinate when disease and vaccination risks were balanced. Experiments 2 and 3 identify several problems associated with the measures used in earlier studies, and show how these problems could have led to the misleading appearance of majority anti-vaccination preferences. In our data, vaccination intentions appear to be less a function of generalized preferences for action or inaction than they are of the regret respondents expect to feel if vaccination or non-vaccination were to lead to a poor outcome. Regret-avoiding choices led some respondents to favor vaccination, others to oppose it. In two follow-up studies, few respondents mentioned action or inaction per se in explaining their choices. We conclude that there is no convincing evidence that a generalized "omission bias" plays any important role in vaccination decisions.

Original languageEnglish (US)
Pages (from-to)186-202
Number of pages17
JournalOrganizational Behavior and Human Decision Processes
Issue number2
StatePublished - Jul 2003
Externally publishedYes


  • Action
  • Justification
  • Omission bias
  • Regret
  • Vaccination

ASJC Scopus subject areas

  • Applied Psychology
  • Organizational Behavior and Human Resource Management


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