Background: the relationship between sample size and errors of the first and second type, which are taken in those studies, where there are properly supported hypotheses, who is detailed in the classical literature; but without indicating a design of the methodology to follow. Aims: to design a methodology to establish the concordance between the sample size, the first and second gender errors of the experimental data. Method: mathematical and statistical methods, procedures, and algorithms are applied, combined with theoretical methods: analysis-synthesis, induction-deduction, and abstraction-concretion to determine the size of the sample, based on fixing the errors first and second gender. The empirical methods applied are framed mainly in the observation of the records of the experimental data, the bibliographic review, in order to deepen the problem and obtain information on the main difficulties that affect the research process.. Results: a methodology is designed, in which the correspondence between the minimum size of the sample and the errors of the first and second gender is established with a preset significance level, according to the experimental data of the study. Conclusions: through elaborated health situations, the need to establish a methodology as a work tool to determine the concordance between the sample size, the errors of the first and second gender a and b is evidenced; in research with a predetermined significance level, based on experimental data in clinical trials, controlled and randomized studies in medicine.