The disorders discussed here are mental disorders, because one or more significant symptoms of psychological disorder. It does not mean that the cause is psychological. The modern principle of psychology is that every psychological phenomenon is caused by a physical process. Psychiatric disorders are common, though few people are out there. It's (still) a taboo. You may be something wrong with your leg, but if you have a psychological problem, it's your own fault, is the idea. Yet it appears that about half of the population once in their life has had a mental disorder. And nearly one third during the past year had a mental disorder.