Lead Poisoning and Intelligence: A Search for Cause and Effect in the Scottish Mental Surveys

Table 1

Distributions of high and low scorers by gender for both the 1932 and 1947 verbal tests as reported by the Survey’s authors.

Distribution of verbal test scores for all high and low scorers, 1932 and 1947
		Low scores (range 0–19)	High scores (range 60–76)	Total in cohort
Boys born in 1921	N (%)^+	8672 (19.6)	1881 (4.3)	44,210
Girls born in 1921	N (%)^+	7753 (17.9)	1428 (3.2)	43,288
Boys born in 1936	N (%)^+	6773 (18.9)	2168 (6.0)	37,998
Girls born in 1936	N (%)^+	4907 (14.0)	2098 (5.9)	37,213

The intelligence test used in both 1932 and 1947 was an instrument developed originally for the placement of students into secondary schools in England (Deary [4]). The test included a picture and verbal portion, the latter so called because “it required literacy and numeracy to understand and complete the items” (Deary [4]). The verbal test had a possible score of 76. Adapted from data in Tables 6–9, pp. 83–84, in: The Trend of Scottish Intelligence; The University of London Press, 1949. Used by permission. ⁺ The percentage of high and low scorers in the total cohort, sorted by gender and year of birth, and their numbers.