The data given below were first presented by Brownlee (1965) and have subsequently appeared in Daniel and Wood (1980), Draper and Smith (1981), and Andrews (1974), among other places. The data consist of measurements taken on twenty-one successive days at a plant that oxidizes ammonia into nitric acid. The dependent variable y is stack loss. It is ten times the percentage of ammonia that is lost (in the form of unabsorbed nitric oxides) during the oxidation process. There are three predictor variables: x!, X2, and X3. The first predictor variable is air flow into the plant. The second predictor variable is the cooling water temperature as it enters the countercurrent nitric oxide absorption tower.

The third predictor variable is a coded version of the nitric acid concentration in the absorbing liquid. Analyze these data giving special emphasis to residual analysis and influential observations.

obs. Xl X2 X3 Y obs. Xl X2 X3 Y 1 80 27 89 42 12 58 17 88 13 2 80 27 88 37 13 58 18 82 11 3 75 25 90 37 14 58 19 93 12 4 62 24 87 28 15 50 18 89 8 5 62 22 87 18 16 50 18 86 7 6 62 23 87 18 17 50 19 72 8 7 62 24 93 19 18 50 19 79 8 8 62 24 93 20 19 50 20 80 9 9 58 23 87 15 20 56 20 82 15 10 58 18 80 14 21 70 20 91 15 11 58 18 89 14