The participants of the Lothian Birth Cohort 1921 were recruited to the project because they had taken part in the Scottish Mental Survey 1932.
The Scottish Mental Survey 1932 was carried out by the Scottish Council for Research in Education. The Survey aimed to test the intelligence of all children born in 1921 and attending Scottish schools on June 1, 1932. The objectives of the study were: (a) to discover the rates of mental deficiency in Scotland; and (b) to obtain information about the distribution of intelligence throughout the community. This massive exercise was Scotland's contribution to the International Conference on Examinations, funded by the Carnegie Corporation and the Carnegie Foundation, and the International Institute of Teachers College at Columbia University.
Almost every school in Scotland took part. About 95% of the available, 1921-born population was tested. A few private schools did not take part. We have since discovered other small-scale omissions, such as individual schools that did not receive test papers and others that received too few. Intelligence test data were obtained for 87,498 children: 44,210 boys and 43,288 girls. Scotland is the only country ever to have tested an entire year-of-birth in its population.
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. There were two short picture tests also, designed for the children who found the Moray House Test too difficult.
The Moray House Test did not give IQ estimates. Therefore, in the summer of 1932, a subsample of 1,000 pupils was given the Stanford Revision of the Binet Intelligence Scale. This sample is often referred to as the Binet 1000. The attempt was to make this 1,000 as representative of the Scottish 11-year-old population as possible, by sampling all educational areas. In the end, 847 children born between April and July 1921 were tested on the Binet. The Moray House Test correlated about .8 (.81 in the boys, .78 in the girls) with Stanford–Binet scores, providing validity for the Moray House Test.
Further reading on the Scottish Mental Survey 1932
- 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 of 1932 and summarises its results.
- Scottish Council for Research in Education. (1933). The intelligence of Scottish children: A National Survey of an age-group. London: University of London Press. This is the detailed account of the results of the Scottish Mental Survey 1932 by the organization who organized the Survey and analysed and wrote up the results.