 The diagnostic reliability is still an essential component to modern versions of the Manual.He was also among the first psychiatrists to study twins as a way to investigate the role of heredity in mental illness and contributed to the knowledge of genetic vulnerability to alcoholism and schizophrenia.Feighner, JP, Robins, E, Guze, SB, Woodruff, RA Jr, Winokur, G, Munoz, R. Diagnostic criteria for use in psychiatric research.