Commentary: Economic growth is the basis of mortality rate decline in the 20th century—experience of the United States 1901–2000

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Abstract
Background The hypothesis that economic growth has been the principal source of mortality decline during the 20th century in the United States is investigated. This hypothesis is consistent with the large epidemiological literature showing socioeconomic status to be inversely related to health status and unemployment associated with elevated morbidity and mortality rates. Despite evidence over many years showing economic growth, over at least a decade, to be fundamental to mortality rate declines and unemployment rates showing lagged, cumulative effects on mortality rate increases, a recent paper argues that the impact of economic growth is to increase the mortality rate. Methods This study utilizes age-adjusted mortality rates over 1901–2000 in the United States as the outcome measure, while independent variables include real GDP per capita in purchasing power parity, the unemployment rate, and the employment to population ratio. A basic interaction model is constructed whereby (i) real GDP per capita, (ii) the unemployment rate, and (iii) the multiplicative interaction between real GDP per capita and the unemployment rate are analysed in relation to age-adjusted mortality rates. The Shiller procedure is used to estimate the distributed lag relations over at least a decade for variables (i), (ii), and (iii). The error correction method is used to examine these relations for both levels and annual changes in independent and dependent variables. Results While GDP per capita, over the medium- to long-term, is strongly inversely related to mortality rates during 1901–2000, in the very short term—i.e. within the first few months—rapid economic growth is occasionally associated with increased mortality rates estimated in annual changes. With respect to the unemployment rate, the first year (without lag) will frequently be associated with a decrease in mortality, but thereafter, and at least for the following decade, the effect is to increase the mortality rate. Thus, the net effect of increased unemployment is a substantial increase in mortality. This is also reflected in the entirely negative relation between the cumulative effects of the employment to population ratio and mortality rates over a decade. Conclusions Economic growth, cumulatively over at least a decade, has been the central factor in mortality rate decline in the US over the 20th century. The volatility of rapid economic growth as it departs from its major trend, has a very short-term effect (within a year) to increase mortality—partly owing to adaptation to new technology and the adjustment of the formerly unemployed to new jobs, social status, and organizational structures.