Consider the following summary data on the modulus of elasticity (×10^6 psi) for lumber of three different grades [in close agreement with values in the article "Bending Strength and Stffness of Second-Growth Douglas-Fir Dimension Lumber" (Forest Products J., 1991: 35-43), except that the sample sizes there were larger]:
Grade J xi si
1 10 1.63 .27
2 10 1.56 .24
3 10 1.42 .26
Use this data and a significance level of .01 to test the null hypothesis of no difference in mean modulus of elasticity for the three grades