A potentially valuable measure of overconfidence on probabilistic multiple-choice tests was evaluated. The measure of overconfidence was based on probabilistic responses to nonsense items embedded in a vocabulary test. The test was administered under both confidence response and conventional choice response directions to 208 undergraduate educational psychology students. Measures of vocabulary knowledge based on confidence and choice responses, overconfidence, and risk-taking propensity were obtained. The results indicated that overconfidence was significantly related in a negative direction to probabilistic vocabulary scores. A moderate correlation was found between overconfidence and risk-taking propensity. However, the scatter plot for these measures showed that this relationship may have been spurious. (Author)