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Sibship size and birth order

It became apparent that the North East of Scotland Psychiatric Case Register could be used to study a variety of social and familial factors in mental illness (Birtchnell, 1973); but it must be emphasised that the NESPCR was unique in recording these kinds of data, and that other case registers could not have been used in this way. Gradually I moved away from parent death studies; and sibship size and birth order was one area I moved into.

Up to this time, studies of sibship size and birth order had relied upon calculating expected birth order positions using the Greenwood Yule method. In many studies, using this method, it was shown that there was an overrepresentation of psychiatric patients in the younger sibling positions. Workers did not seem to appreciate that this was because, by the time the study was carried out, the older siblings would have died. In my postal survey for the parent death comparisons I had enquired about sibship size and birth order. This enabled me to show that there was a clear relationship between year of birth and sibship position. When I did direct comparisons between patient data and control data I was able to demonstrate that there was no association between sibship size or birth order and proneness to mental illness. With the large numbers of subjects in the case register and the population samples I was able to examine sibship constellations in detail, and again demonstrate that no sibship position carried an increased risk for mental illness.

In those days there was an influential book by the German psychologist called Walter Toman, which proposed various reasons why people were attracted to those who occupied reciprocal sibship positions, e.g. younger brothers were attracted to older sisters; and why people who had such reciprocal relationships would prosper. Using data collected (1) from market research interviews and (2) from a student survey carried out by Julie Mayhew, I was able to demonstrate that Toman's (1993) ideas could not be supported.



Birtchnell, J. (1970) Sibship size and mental illness. British Journal of Psychiatry, 117, 303‑308.

Birtchnell, J. (1971a) Mental illness in sibships of two and three. British Journal of Psychiatry, 119, 481‑487.

Birtchnell, J. (1971b) Birth rank and mental illness. Nature, 234, 485‑487.

Birtchnell, J. (1972) Birth order and mental illness: a control study. Social Psychiatry, 7, 167‑179.

Birtchnell, J. (1973) The use of a psychiatric case register to study social and familial aspects of mental illness. Social Science and Medicine, 7, 145‑153.

Birtchnell, J. & Mayhew, J. (1977) Toman's Theory: tested for mate selection and friendship formation. Journal of Individual Psychology, 33, 18‑36.

Toman, W. (1993) Family Constellation: Its Effects on Personality and Social Behavior. (4th Edition) New York: Springer.