Empirical approach to sample size estimation for testing of AI algorithms

Calculation of sample size is one of the basic tasks in the field of correct and objective testing of artificial intelligence (AI) algorithms. Existing approaches, despite their exhaustive theoretical justification, can give results that differ by an order of magnitude under the same initial conditions. Most of the input parameters for such methods are determined by the researcher intuitively or on the basis of relevant literature data in the subject area. Such uncertainty at the research planning stage is associated with a high risk of obtaining biased results, which is especially important to take into account when using AI algorithms for medical diagnosis. Within the framework of this work, an empirical study of the value of the minimum required sample size of radiology diagnostic studies to obtain an objective value of the AUROC metric was conducted. An algorithm for calculating the threshold value of sample size according to the criterion of no statistically significant changes in the metric value in case of increasing this size was developed and implemented in software format. Using datasets containing the results of testing of AI algorithms on mammographic and radiographic studies with the total volume of more than 300 thousand, the empirical threshold for the sample size from 30 to 25 thousand studies with different relative content of pathology – from 10 to 90% – was calculated. The proposed algorithm allows us to obtain results invariant to the balance of classes in the sample, the target value of AUROC, the modality of studies and the AI algorithm. The empirical value of the minimum sufficient sample size for testing the AI algorithm for binary classification, obtained by analysing over 2 million estimated values, is 400 studies. The obtained results can be used to solve the problems of development and testing of diagnostic tools, including AI algorithms.