The accompanying observations on axial stiffness index resulted from a study of metal-plate connected trusses in which five different plate lengths—4 in., 6 in., 8 in., 10 in., and 12 in.—were used (“Modeling Joints Made with Light-Gauge Metal Connector Plates,” Forest Products J. 1979: 39–44).

Use the Kruskal–Wallis test to decide at significance level .01 whether the true average axial stiffness index depends somehow on plate length.

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i = 1 (4 in.): i = 2 (6 in.): i = 3 (8 in.): i = 4 (10 in.): i = 5 (12 in.): 309.2 309.7 311.0 326.5 349.8 409.5 331.0 347.2 348.9 381.7 402.1 404.5 357.1 366.2 351.0 382.0 392.4 409.9 346.7 362.6 384.2 410.6 433.1 452.9 461.4 410.7 419.9 465.8 473.4 407.4 441.8 316.8 361.0 367.3 441.2