What is MRS?
The idea of minimum required score was introduced by L . Nedelsky (Nedelsky L "Absolute grading standards for objective tests. Educ. Psychol. Meas. 14:3-1,1954).  According to that idea the professor analyzes the difficulty of every question from the point of view of minimum required knowledge in order to pass the test (student that will get a D). The professor should identify themselves with the student who knows just enough to pass (grade D) and evaluate how such a student should answer a question.

How to estimate MRS?
Defining of MRS can be explained in detail on the example of multiple choice questions. Other types of questions can be evaluated in the same way, but the assessment procedure is more complex. 

     If a question is very difficult and the "D" student may not recognize the right answer, but randomly choose one of equally attractive answers, their chance to guess the right answer is 1:5 (i.e. 20%), so the question is graded as MRS difficulty = 1/5 = 0,2.
     However, if one of the answers is so obviously incorrect that a "D" student simply must recognize it, is left with the other four equally attractive answers to choose from and chooses one randomly. MSR in this case is 1/4 = 0,25.
     In an even easier question they will recognize 2 distracters which are obviously incorrect, so they can randomly choose from the other three answers. In that case the MSR is 1/3 = 0,33.
     In an even easier question we allow the students with borderline knowledge to decide between two answers (while they must recognize the other three as incorrect). MPR in that case is 1/2 = 0,5.
     And finally, if the question is so easy that the student that knows enough to be graded as "D" has to recognize the right answer (or the four incorrect answers), MPR of the question is 1.


 MRS can be increased, if the correct or incorrect answer that a "D" student has to recognize is awarded 2 points (instead of 1 like in the previous case), and in an easier exam 0 points (so called Chicago scale). The advantage of this approach lies in the fact that uncertain distracters (ones for which the professors cannot decide whether a "D" student should recognize or not) are assigned one point.

 Questions should be independently graded by at least three professors, and in a case of greater discord (more than one grade on the scale), they should jointly decide on the grade. It is even better if the questions are graded by all available professors, which should, in a case of discord, all agree on the grade or leave that decision to be made by a "senior" board consisting of three members. That way a bank of standardized questions is created where each of the questions is MRS graded.

 Why MRS?
The main reason to determine the MRS for each question lies in defining the difficulty of a question, checking the distracters, comparing them with the established goals of the course and creating a unified bank. Another reason is the unification of the quality and difficulty of a test given at different times and repeatedly, as well as determining the suitable grading scale. This results in absolute objective grading standard, i.e. absolute accepted and agreed upon criteria of the professors about the minimum level of knowledge necessary for students to pass a test.