Table 15.5.4 shows the average quality scores for production, averaged according to which supplier (A, B, or C) provided the materials and which shift (day, night, or swing) was active at the time the part was produced; this is followed by the computer version of the ANOVA table. For this experiment, there were five observations for each combination (a combination specifies both supplier and shift). Note that the last row (and column) represents the averages of the numbers in their column (and row), respectively (e.g., 82.42 is the average quality for Supplier A across all shifts).
a. Compare the overall average for supplier A to that for suppliers B and C. Does it appear that there are large differences (more than two or three quality points) among suppliers?
b. Are the average supplier scores significantly different? How do you know?

TABLE 15.5.4 Average Quality Scores and ANOVA Table Supplier A Supplier B Supplier C Average Analysis of Variance for Quality Day Shift 77.06 81.14 82.02 80.08 Night Shift 93.12 88.13 81.18 8748 Swing Shift 77.06 78.11 79.91 78.36 Average 82.42 8246 81.04 81.97 DF MS shift supplier shift supplier Error Total 2 4. 36 704.07 19.60 430.75 1062.05 2216.47 352.04 9.80 107.69 29.50 11.93 0.33 3.65 0.000 0.720 0.014