In today’s item response theory (IRT) the response to the test item is considered as a probability event depending on the student’s ability and difficulty of items. It is noted that in the scientific literature there is very little agreement about how to determine factors affecting the item difficulty. It is suggested that the difficulty of the item increases with the number of key elements, which are the data elements used in solving the item. Based on the statistical analysis of solutions of specially designed test items it has been concluded that there is a linear dependence of the item difficulty in the Rasch model on the number of key elements of the solution. The result allows taking an unbiased look at the difficulty of test items at the stage of their development, as well as predicts the outcome of testing. 

Andreev, V.I. (2000). Education: Training for creative self-development. Kazan: Center for Innovative Technologies.

Ball, G.A. (1990). The theory of academic pursuits: Psychology and education aspect. Moscow: Pedagogic.

Chelyshkova, M.B. (2002). Theory and practice of designing educational tests. Moscow: Logos.

Crocker, L. & Algina, J. (2010). Introduction to classical and modern test theory. Moscow: Logos.

Dzhalmuhambetov, A.U. & Stefanova, G.P. (2009). Tasks - problems, tasks assessment on physics, methods of their solution: the manual. Astrakhan: Izd Gos.ped.un.

Gilev, A.A. (2007). Cognitive analysis of the process of training solutions of physical problems. Physics in Higher Education, 2, 26-37.

Gilev, A.A. (2008). Workshop on the decision of physical problems in a technical college: the manual. St. Petersburg: Lan 'Publisher.

Gilev, A.A. (2011c). Cognitive competences: development and diagnostics in the physics course of the higher technical school. Samara: SGASU.

Gilev, A.A. (2011b). Level measurement logical inference. Proceedings of the SFU. Jurisprudence, 8, 175-180.

Gilev, A.A. (2011a). Quality diagnosis of cognitive processing verbal information in solving physical problems. Physics in Higher Education, 17, 16-27.

Gilev, A.A. (2016). Methodical system of cognitive competence development of students in teaching physics: monograph. Samara: SGASU.

Kim, V.S. (2007). Testing of educational achievements. Ussuriisk: University press UGPI.

Lerner, I.Ya. (2000). Problem-based learning, The theory and methods of learning physics in school: General quesrions. In S.E. Kamenetski, N.S. Purysheva (Eds.). Moscow: Publishing center “Academy”.

Neiman, Yu.M. & Khlebnikov, V.A. (2000). Introduction to the theory of modeling and parameterization of education tests. Moscow: Nauka.

Osipov, P.N. & Marshalova, I.N. (2013). Formation of research competence of the future engineers in design activity. Herald of Kazan Technological University, 16, 194-197.

Popov, L.M. & Ibragimov, E.N. (2007). Psychology intellectual development of the student-activity. Scientific notes of the Kazan State University, 149, 5-19.

Popov, L.M., Ustin, P.N. & Molchanov, E.I. (2009). Orientation of students on the intellectual and ethical self-development and self-development. Education, 6(16), 3-8.

Stenner, A.J., Wright, B.D. & Linacre, J.M. (1994). From P-values and raw score statistics to logits. Direct access:  http://www.rasch.org/rmt/rmt81.htm.

Volov, V.T. & Kaptsov, A.V. (2009). Methods of diagnosis and management of the dynamics of socio-psychological characteristics of the person based on the information and thermodynamic approach. Bulletin of the University of RAO, 9, 60-64.

Volov, V.T. (2007). On the principles of the system of education. Philosophy of Education, 4(21), 4-11.