By using confidence marking (CM) along with multiple-choice questions, an examiner needs to measure the consistency and adequacy of CM usage with the instructions given to the student. This measure is called the “realism of the subject”. Although it is easy to compute, the current realism formula entails some conceptual, probabilistic and computational weaknesses. Relying on probability theory and a set of statistically justified arguments, this paper shows a new approach to calculate realism that has a better match to the definition of CM and to the way examiners ask the students to use it. Moreover, the new realism is more precise with respect to the previous and gives a better indication of the student’s self-evaluation skills and his ability to use CM. Finally, this will improve the reliability of items quality indicators which use realism in their calculations such as Gilles’ rpbisSCT (2002).