1. General relationship between health and air quality widely accepted Empirical estimates should inform public policy Difficult to establish cause/effect

2. For example: polluted air typically is polluted in a number of ways Difficult to separate effects of individual pollutants “External Health Costs of a Steel Mill” studies relationship between operation of steel mill in Utah and local health Utah Valley is an area in Utah that includes cities of Provo and Orem

3. Steel mill, built in 1940’s, is large source of air pollution in the valley During winter temperature inversions, mill found to contribute over half total particulate matter in area PM 10, air pollution generally would have greatest health effect on respiratory system Associated with such diseases asthma, bronchitis and influenza

4. Paper looks at relationship between hospitalizations/deaths and operation of mill Compares Utah Valley to nearby Cache Valley Two areas are similar in characteristics that can affect health – Smoking incidence, temperature, housing etc. Steel mill too far from Cache to affect air quality in area

5. Utah valley violated PM 10 standards on average 12 days a year when the mill is open, zero when it is closed Cache Valley never recorded PM 10 violation The mill closed for a year in 1986

6. Study argues natural experiment might capture effect of mill that are missed by studies based on measured pollution levels Difficult to measure exactly what’s in the air PM 10 caused by mill may be more toxic than normal Closing of mill represented large, discontinuous change in air quality

7. Collects hospital admissions data for respiratory and cardiovascular diseases over 1985 to 1991 Compares statistics when mill is open to when it is closed Summary Statistics