Desiring to grade timber mechanically, engineers studied the modulus of rupture in lb/in.2, for a sample of untreated green, 7 inch by 9 inch, mixed oak timbers, sorted by grade: select structural, No. 1, No. 2, and below grade. A one-way ANOVA was performed to test
H0: µselect = µNo. 1 = µNo. 2 = µbelow grade. The null hypothesis was rejected with a P-value of 0.018. The engineers proceeded to conduct Tukey's test to determine which pairwise means differed using Minitab. The results are presented next. Which pairwise means differ? What do you conclude from the test?
1 = select structural, 2 = No. 1, 3 = No. 2, and 4 = below grade.
Tukey's Pairwise Comparison
Family error rate 5 0.0500
Individual error rate 5 0.0108
Critical value 5 3.86
Intervals for (column level mean) 2 (row level mean)

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-6.914 13.064 1.936 -1.139 18.839 21.914 -2.989 -6.064 -14.914 16.989 5.064 13.914 2. 3.