The Environmental Protection Agency releases figures on urban air soot in selected cities in the

United States. For the city of St Louis, the EPA claims that the average number of micrograms suspended particles per cubic meter of air is 82. Suppose St Louis officials have been working with business, commuters, and industries to reduce this figure. These city officials hire an environmental company to take random measures of air soot over a period of several weeks. The resulting data follow. Use these data to determine whether the urban air soot in St Louis is significantly lower than it was when the EPA conducted its measurements, assuming you want to take only 3% risk of committing a Type I error.

Data

81.6 66.6 70.9 82.5 58.3 71.6 72.4 96.6 78.6 76.1 80 73.2 85.5 73.2 68.6 74

68.7 83 86.9 94.9 75.6 77.3 86.6 71.7 88.5 87 72.5 83 85.8 74.9 61.7 92.2

A. POPULATION

• Determine the population type

• Describe (in words) the population characteristic

• State H0 and Ha ( in words and using μ or p)

• Describe a Type I error and a Type II error IN CONTEXT

B. STATISTICAL METHOD

• How much confidence is desired? determine α

• Write the formula of the test statistic (using the hypothesized value from H0)

• Write the formula for the confidence interval.

• Choose and write your decision criteria ( critical value , p-value, or both )

C. SAMPLE

• Describe the sample and check that the sample meets the necessary assumptions.

D. STATISTICAL RESULTS

• Compute the value of the test statistic

• Compute the p-value, the critical value or both ( based on your decision criteria in B )

• Construct the confidence interval for your population characteristic

E. CONCLUSION

• Make a concluding statement based on your decision criteria and your confidence interval and discuss your finding.