Environmentalists, government officials, and vehicle manufacturers are all interested in studying the auto exhaust emissions produced by motor vehicles. The major pollutants in auto exhaust from gasoline engines are hydrocarbons, carbon monoxide, and nitrogen oxides (NOX). Researchers collected data on the NOX levels (in grams/mile) for a random sample of 40 light-duty engines of the same type. The mean NOX reading was 1.2675 and the standard deviation was 0.3332.

Researchers constructed a 95% confidence interval for the mean amount of NOX emitted by all light-duty engines of this type. Afterwards, the researchers decided that they wanted a 90% confidence level. They then re-calculated the confidence interval at the 90% confidence level.

If all else remains the same, going from a 95% confidence level to a 90% confidence level will have what effect on the width of the confidence interval? (hint: calculate a CI for 95% CL, then 90% CL; what happened to the width?)

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