Samuel H. Preston, UW sociology professor from 1972 to 1977, resolved a long-standing controversy about the reasons for the rapid decline in mortality experienced worldwide during the first half of the twentieth century. And he did so by seemingly doing the impossible: He assembled and analyzed an historical data base of mortality measures from 165 populations, representing 43 nations, for the decades of 1900, 1930, and 1960.
Preston is currently on the faculty of the University of Pennsylvania. But while at the UW, he published findings that shed new light on a controversy that demographers and medical historians had been debating. Some scholars had argued that medical and public health measures were chiefly responsible for the observed decrease in mortality; others had maintained that increasing levels of income and improved nutrition were the cause. Each camp cited evidence from different case studies on specific countries for different time periods.
The solution required Preston to tackle a Herculean task. He had to assemble a comprehensive, worldwide database and study the correlations between national income and life expectancy from the historical data over the entire time period in question. By doing so, Preston showed that economic development, as measured by national income, could only account for about 15-20% of the improvement in life expectancy from the 1930s to the 1960s.
Most of the significant gains in longevity were due to non-economic factors such as public health interventions, improved sanitation, greater access to curative medicines, and behavioral changes that resulted in decreased exposure to disease. In the course of the study, Preston uncovered a common structure in mortality rates by age, sex, and cause of death that varied in predictable patterns as overall mortality fell from high to low levels.