Abstract: A stereotypy test apparatus 10 is disclosed, which is suitable for interactive use in the diagnosis of a psychiatric disorder. The apparatus comprises an input means in the form of a keypad 14 adapted for physical entry of input signals to the apparatus 10 and a control means 28 which is adapted to prompt a candidate to enter during a test session a succession of said input signals. The control means 28 analyses entered said input signals in order to derive and output from said analysis one or more output signals indicative of at least one value RC, RS which is used in the diagnosis of the presence or absence in said candidate of at least one predetermined psychiatric disorder or of the candidate's predisposition theretowards. The input signals comprise a succession of choices (1-9) selected freely by said candidate from a plurality of mutually independent choices (1-9) and a said output signal RC, RS is indicative of repetitive patterns among said candidate choices.