The Scottish Mental Survey of 1947

The foundation of the Lothian Birth Cohort 1936 study is a national survey of general intelligence conducted in Scotland in 1947. The participants who were recruited for the study at the University of Edinburgh in 2004 had taken part in the Scottish Mental Survey of 1947. This page reviews the origin of the data and the historical context in which the Survey was carried out.

Comparing intelligence of two birth cohorts of Scottish 11-year-olds

Old school photograph

The Survey aimed to test the intelligence of all children born in 1936 and attending school in Scotland in June 1947.  It was intended to repeat, and for its results to be compared with, the Scottish Mental Survey of 1932. The motivation for the 1947 Survey was a concern that the mean intelligence level of the United Kingdom might be decreasing. It was thought that this was because people in larger families had lower average intelligence test scores than those in smaller families.

On 4 June 1947, almost all 1936-born children attending Scottish schools were given the same Moray House Test that had been used in the Scottish Mental Survey of 1932. Intelligence test data were obtained for 70,805 children: 35,809 boys and 34,996 girls.

The Moray House Test repeated

The intelligence test used was a specially-prepared version of the Moray House Test No. 12. The test was devised by Professor Godfrey Thomson who was Bell Professor of Education at the University of Edinburgh from 1925 to 1951.

The Moray House Test No. 12 had 71 items plus eight practice items. A score of 76 was the maximum possible in the Moray House Test.

Unexpected test results

The results were the opposite of those predicted. The Scottish nation's Moray House Test scores of 1936-born children showed a slight increase from those born in 1921. The average score in the Scottish Mental Survey 1932 was 34.5 out of 76. The average score in the Scottish Mental Survey 1947 was 36.7 out of 76.

Further reading on the Scottish Mental Survey of 1947

Deary, I. J., Whalley, L. J., & Starr, J. M. (2009). A lifetime of intelligence: follow-up studies of the Scottish Mental Surveys of 1932 and 1947. Washington, DC: American Psychological Association.

  • Chapter 1 of this book describes the history of the Scottish Mental Survey 1947 and summarises its results.

Scottish Council for Research in Education. (1949). The trend of Scottish intelligence: A comparison of the 1947 and 1932 surveys of the intelligence of eleven-year-old pupils. London: University of London Press.

  • This is the detailed account of the results of the Scottish Mental Survey 1947, and how it compared with the Scottish Mental Survey 1932, by the organization who arranged the Surveys and analysed and wrote up the results.

Watch a video of exhibition ‘Godfrey Thomson: the man who tested Scotland’s IQ’ with Professor Ian Deary’s commentary