Valuations and appraisals are the product of human judgement. This paper explores the contention that such judgement may incorporate elements of cognitive bias. It assumes that a clearer grasp of the impact of such bias may assist in understanding what leads to 'inaccuracy' in valuations. It outlines the case for questioning the validity of the rational assumptions that underlie models of valuation behaviour, and focuses upon one particular form of deviation from rationality: confirmation bias. It presents and discusses the results of a survey designed to test for associations of characteristics that might support the case for the presence of confirmation bias in valuer behaviour. It concludes that the case for the presence of confirmation bias is unproved.