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Abstract Introduction Psychometrics plays a vital role in evaluating educational research, including the analysis of multiple-choice exams. This study aims to improve the discriminatory ability of the “Médico Interno Residente” (MIR) medical exam in Spain, used to rank candidates for specialized healthcare training, through psychometric analysis. Methods We analyzed 2,890 MIR exam questions from 2009 to 2021 (totaling 147,214 exams), categorizing them based on methodology and response type. Evaluation employed classical test theory and item response theory (IRT). Classical test theory determined difficulty and discrimination indices, while IRT assessed the relationship between knowledge levels and question performance. Results Question distribution varied across categories and years. Frequently addressed knowledge areas included various medical specialties. Non-image-associated clinical cases were the easiest, while case-based clinical questions exhibited the highest discriminatory capacity, differing significantly from image-based case or negative questions. High-quality questions without images had longer stems but shorter answer choices. Adding images reduced discriminatory power and question difficulty, with image-based questions being easier. Clinical cases with images had shorter stems and longer answer choices. Conclusions For improved exam performance, we recommend using a clinical case format followed by direct short-answer questions. Questions should be of low difficulty, providing clear and specific answers based on scientific evidence and avoiding ambiguity. Typical clinical cases with key characteristic features should be presented, excluding uncertain boundaries of medical knowledge. Questions should have lengthy stems and concise answer choices, minimizing speculation. If images are used, they should be typical, clear, consistent with the exam, and presented within clinical cases using clinical semiotics and propaedeutics.

This research explores the results that an examinee would obtain if taking a multiple-choice questions test in which they have doubts as to what the true answer is among different options. This problem is analyzed by making use of combinatorics and analytical and sampling methodologies. The Spanish exam through which doctors become medical specialists has been employed as an example. Although it is difficult to imagine that there are candidates who respond randomly to all the questions of such an exam, it is common that they may doubt over what the correct answer is in some questions. The exam consists of a total of 210 multiple-choice questions with 4 answer options. The cut-off mark is calculated as one-third of the average of the 10 best marks in the exam. According to the results obtained, it is possible to affirm that in the case of doubting over two or three of the four possible answers in certain group questions, answering all of them will in most cases lead to obtaining a positive result. Moreover, in the case of doubting between two answer options in all the questions of the MIR test, it would be possible to exceed the cut-off mark.