To demonstrate that at least one of their ideas was correct, they turned to the Philippines. Here, a study called the Cebu Longitudinal Health and Nutrition Survey has been going on since 1983. It follows the lives of Filipina mothers and those of their children born in 1983 and 1984. Among the data collected were records of the vaccinations these children received as infants and also their scores in language, maths and IQ tests at the age of ten.
The three researchers organised children whose social circumstances were similar into groups, depending on whether or not the children had been vaccinated against a range of diseases including measles, polio and tuberculosis. They then compared test scores between groups. They found a statistically significant difference in the language and IQ scores between otherwise comparable vaccinated and unvaccinated children. In both cases, those of the unvaccinated were lower. Since it is known from other studies that these scores are good predictors of adult income, the researchers concluded that childhood vaccination would have significant economic benefits.
