An examinee is required to express his confidence in the correctness of each choice of a multiple-choice item in a probabilistic test. For the responses to be valid indicators the confidence expressed in each choice should be determined by an examinees' knowledge. This study assessed the relationship of the certainty of examinees' responses to knowledge and selected personality traits. It was found that a reliable certainty of responses was exhibited by examinees. This certainty measure had a moderately high (.62) relationship to examinees' knowledge. The certainty of response was also related to risk taking holding knowledge constant. For related document see TM003533. (Author)