An analysis of familial data on psychiatric patients: parental age, family size, birth order, and ordinal position.

Most mature students of human personality are agreed that normal and abnormal characteristics are determined by the complex interaction of numerous biological (e.g. genetic, neuro-endocrine, or metabolic), psychological, social, and cultural factors (Kluckhohn, Murray, and Schneider, 1953). However, there still exist wide differences of opinion as to the relative importance of various determinants in the causation of specific anomalies -of personality and behaviour. While we are sometimes told that the nature-nurture controversy has long since been resolved, there are still many who view personality and its aberrations predominantly from either a genetical or an environmental aspect. The divergent opinions frequently represent at best no more than educated guesses, and at worst merely personal bias which results in unsolved problems being approached with preconceived convictions and consequent distortion of both observations and their interpretation. Among the important consequences of differences in the orientation of the observer is the interpretation placed on studies of the families of mentally ill patients. There is much evidence of greatly increased incidence of mental illness among other members of the families of patients with certain mental disorders (e.g. Pollock, Malzberg, and Fuller, 1939; Kallmann, 1953). However, while some authorities maintain that such intra-familial concentration of these disorders represents mainly random genetic transmission (e.g. Kallmann, 1952, 1953; Slater, 1950, 1953), others regard transmission from parent to child as the result of harmful early experiences associated with intricate intra-familial relationships (e.g. Masserman, 1946; Lidz and Lidz, 1949; Weiss and English, 1949; Gerard and Siegel, 1950; Bowlby, 1952; Lidz, Parker and Cornelison, 1956). In view of the observed concentration of mental disorders in the families of some patients, and the amount of speculation concerning both genetic transmission (Penrose, 1950) and functional interpersonal relationships or dynamics (Cleckley and Thigpen, 1955), it is at first sight remarkable how little is yet known about the structure or composition of the families of the mentally ill. It might perhaps be argued that without such information our investigations of function bear some similarity to the study of physiology in the absence of any knowledge of anatomy. However, the accumulation and analysis of data concerning the families of the mentally ill present serious technical difficulties and have often yielded barren results. Nevertheless, this is a most important area deserving the attention of both the biologistand the social scientist. Among the familial studies that have been undertaken hitherto have been a number of investigations of parental age, family size, birth order, and ordinal position. Scientific interest in these variables developed during the latter part of the 19th century, in association with publications by Galton and other writers on heredity and eugenics. In the early years of the 20th century several quite extensive studies of family size and birth order were made, but early statistical techniques of analysis led to erroneous conclusions.