The regulatory board of health in a particular state speci?es that the ?uoride levels in water must not exceed 1.5 parts per million (ppm). The 20 measurements given here represent the randomly selected daily early morning readings on ?uoride levels in water at a certain city.
0.88 0.82 0.97 0.95 0.84 0.90 0.87 0.78 0.75 0.83
0.71 0.92 1.11 0.81 0.97 0.85 0.97 0.91 0.78 0.87
Test the hypothesis that the median ?uoride level for this city is 0.90 against the alternative that the median is different from 0.9 at α = 0.01, using (a) the large sample sign test, and (b) the Wilcoxon signed rank test. Interpret the results.