The Effect Of Air Pollution On Life Expectancy
Many scientists believe that air pollution is hazardous
to human health, yet they cannot run laboratory experiments on humans to
confirm this theory. Instead, they must make do with
“nature’s
data,” statistics
showing that life expectancies are lower and incidence of respiratory disease
is higher for people living in cities with substantial air pollution. But
perhaps these grim statistics can be explained by other factors—that
the population of cities tends to be older, gets little exercise, and can
be aggravated by a rushed lifestyle.
Multiple regression techniques can be used in place of laboratory experiments to control for these other factors. One study used biweekly data from 117 Standard Metropolitan Statistical Areas to estimate the following equation:
| Y | = | 19.61 | + | 0.041X1 | + | 0.71X2 | + | 0.001X3 | + | 0.41X4 | + | 6.87X5 |
| [2.5] | [3.2] | [1.7] | [5.8] | [18.9] |
| where | Y | = | mortality rate, per 10,000 population (average = 91.4) |
| X1 | = | average suspended particulate reading (average = 118.1) | |
| X2 | = | minimum sulfate reading (average = 4.7) | |
| X3 | = | population density per square mile (average = 756.2) | |
| X4 | = | fraction of population that is nonwhite (average = 12.5) | |
| X5 | = | fraction of population 65 and older (average = 8.4) | |
| [ ] | = | t-values |
The inclusion of the last three explanatory variables is intended to accomplish the same objectives as a laboratory experiment, in which these potential influences on mortality are held constant to isolate the effects of pollution on mortality. The two pollution measures both have substantial and statistically significant effects on mortality. For the average city, a 10 percent increase in the average suspended particulate reading, from 118.1 to 129.8, increases the mortality rate by 11.81(0.041) = 0.48. A 10 percent increase in the minimum sulfate reading increases mortality by 0.47(0.71) = 0.34.
Lave, Lester B., and Eugene P. Seskin, “Does Air Pollution Shorten Lives?,” Statistical and Mathematical Aspects of Pollution Problems. Ed. John W. Pratt. New York: Marcel Drekker, 1974.
Smith, Gary. Statistical Reasoning. 3rd edition. United States: McGraw-Hill, Inc., 1994.
