A computer implemented method and computer system for generating a diagnostic tool for diagnosis of a behavioural disorder of a subject by applying machine learning to a diagnostic instrument for diagnosis of the behavioural disorder are disclosed. The diagnostic instrument comprises a set of diagnostic questions and corresponding selectable answers. The computer system comprises one or more processors； and memory to store: one or more computer programs. The one or more computer programs comprising instructions for receiving as input diagnostic outcomes and selected answers to the set of diagnostic questions of a plurality of subjects previously evaluated for the behavioural disorder, analysing the diagnostic outcomes and the selected answers of the plurality of previously evaluated subjects with the machine learning to construct a behavioural classifier to distinguish among previously evaluated subjects with different diagnostic outcomes with the behavioural classifier comprising a subset of the set of diagnostic questions and corresponding selectable answers from the diagnostic instrument, determining the accuracy of the behavioural classifier comprising the subset of diagnostic questions and corresponding selectable answers, by testing the behavioural classifier against an independent source of clinical data where the behavioural classifier comprising the subset of diagnostic questions and corresponding selectable answers has an accuracy over 90%, generating the diagnostic tool for diagnosis of the behavioural disorder, where the diagnostic tool comprises the behavioural classifier and the subset of diagnostic questions and corresponding selectable answers having the accuracy greater than 90%, and configuring a computing device accessible by a user to display the subset of diagnostic questions and corresponding selectable answers to the user, to collect user selected answers for the subset of diagnostic questions, and to provide the user selected answers as input
