Clinical Psychometrics is an introduction to the long-term attempt to measure the psychiatric dimension of dementia, schizophrenia, mania, depression, anxiety, neuroticism, extraversion/introversion and health-related quality of life. The two psychometric procedures, classical factor analysis and modern item-response models, are presented for readers without any requirement for particular mathematical or statistical knowledge. The book is unique in this attempt and provides helpful background information for the dimensional approach that is being used in the forthcoming updates to the diagnostic classification systems, ICD-11 and DSM-5. The book is written for everyone who is interested in the origins and development of modern psychiatry, and who wants to be familiar with its practical possibilities; how it is possible to compare different individuals with each other, how one may determine the boundary between what is normal and what is disease, or how one may assess the clinical effect of the various forms of treatment, available to present day psychiatry.