I analyzed and formulated components related to diagnosis and treatment in psychiatry with special emphasis on patients' individuality in clinical settings. The word "diagnosis" has two meanings: 1) identification of diseases, and 2) conclusion reached, namely, "diagnostic action" and "diagnostic classes", respectively. The diagnostic classes include those led by the conceptual definition and those led by the operational definition. The diagnostic action comprises a naturalistic method and an operational method. I contend that the conceptual definition of diagnostic classes and the naturalistic method of diagnosis should receive more attention. Patients immediately after the first contact or in an early stage of the disease may be given a "vector diagnosis", a set of plural diagnostic options with probability values. As for treatment in the above situation, a framework integrating three components, namely, diagnostic options with probability, treatment options, and gain/risk evaluation, should be kept in mind. In the treatment of a patient after the acute phase and with definite diagnoses, attention should be paid to the patient's unknown variation in the effectiveness of drug treatment. Thus, the protracted use of a single drug with even the most powerful effect may not be superior to algorithm-type drug treatment, where the first drug is changed to the second drug if the patient has not improved satisfactorily, and, again, the second drug is changed to the third, to the fourth, and so on, if favorable remission has not been achieved.
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