This study aimsto explain theconjunction fallacy (Tversky&Kahneman, 1983) in terms of degree of confirmation (Crupi, Tentori, & Gonzalez,2007) by employing corpus data analysis. To accomplish this, wecalculated indexes of the degrees of confirmation fromthe British National Corpus and fitted them to dataof the previous study (Shafir et al., 1990). The resultsshow that a major index of the degree of confirmation(Crupi et al., 2007) can significantly predict theconjunction fallacy, indicating a relationship betweenthe conjunction fallacy and degree of confirmationas well asthe importance of corpus data to explain biasesin judgment.