We have found and would argue that the theories of risk perception and aspects of decision-making under uncertainty have been useful for understanding the differences and similarities between pro-immunisers and non-immunisers, except for the issue of omission bias. Parents in this study, whether immunisers or not, generally did not agree that a negative outcome was preferable or more acceptable from inaction. This finding raises some doubts about the methods and/or generalisability of findings from studies of this phenomenon, which usually involve multiple, similar, hypothetical situations with limited contextual information, presented in mathematical and probabilistic language. Participants in this study responded to these omission bias statements by generally denying that either contributed to their decision to immunise their child.