Two years of rainfall acidity data was analyzed at 9 monitoring stations in the eastern United States. For each of two years, (Sept 1, 1978 to Aug 31, 1980) a rainfall adjusted yearly average pH was calculated by each monitoring station. From previous experience, the sample differences are from a normal distribution.
LOCATION 1 2 3 4 5 6 7 8 9
YEAR 1 (X) 3.78 3.96 4.22 4.00 3.96 4.02 4.16 4.30 4.30
YEAR 2 (Y) 4.08 4.06 4.27 4.29 4.09 4.27 4.31 4.31 4.29
(a) Test at alpha= .01 if there is has been a significant change in pH level over the two years. (use Excel to find d and sd, then do the rest by hand).
(b) Estimate the mean difference in pH level for the two years using a 99% confidence interval.