The participants of the Lothian Birth Cohort 1936 were recruited to the project because they had taken part in the Scottish Mental Survey 1947.
The Scottish Mental Survey 1947 was carried out by the Scottish Council for Research in Education. The Survey's chairman was Professor Godfrey Thomson of the University of Edinburgh. The Survey aimed to test the intelligence of all children born in 1936 and attending Scottish schools on June 4, 1947. It was intended to repeat, and for its results to be compared with, the Scottish Mental Survey 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.
The United Kingdom's Population Investigation Committee of the Royal Commission on Population took advantage of the fact that all Scotland's 1921-born schoolchildren had been tested in 1932. They asked for the idea of the declining national intelligence to be tested in Scotland by the Scottish Council for Research in Education. Thus, the Scottish Mental Survey 1947 was funded by the Nuffield Foundation and the Eugenics Society, via Population Investigation Committee.
On June 4, 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 1932. Intelligence test data were obtained for 70,805 children: 35,809 boys and 34,996 girls. Scotland is the only country ever to have tested an entire year-of-birth in its population, and it did it twice.
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. The items were of a variety of types of mental task: following directions (14 items), same–opposites (11), word classification (10), analogies (8), practical items (6), reasoning (5), proverbs (4), arithmetic (4), spatial items (4), mixed sentences (3), cypher decoding (2), and other items (4). A score of 76 was the maximum possible in the Moray House Test. Eight practice items preceded the test.
The results were the opposite of those that the Population Investigation Committee 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 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 organized the Surveys and analysed and wrote up the results.