Air samples. The air quality data in Exercise 12.5

(Table 12.9) are associated with the summary statistics reported in Table 12.12.

TABLE 12.12 Means and standard deviations for Exercise 12.7.

(a) Calculate the standard error of the mean difference without assuming equal variance.

(b) Calculate a 95% confidence interval for μ1 − μ2 , again without assuming equal variance. Use the conservative degrees of freedom to help calculate the confidence interval.

(c) Determine the two-sided P-value for testing H0 : μ1 = μ2 .