Jaspers' dissatisfaction with the popular understanding of mental illness led him to question both the diagnostic criteria and the methods of clinical psychiatry. He published a paper in 1910 in which he addressed the problem of whether paranoia was an aspect of personality or the result of biological changes. Although it did not broach new ideas, this article introduced a rather unusual method of study, at least according to the norms then prevalent. Not unlike Freud, Jaspers studied patients in detail, giving biographical information about the patients as well as notes on how the patients themselves felt about their symptoms. This has become known as the "biographical method" and now forms a mainstay of psychiatric and above all psychotherapeutic practice.