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Using computer simulated data, the Type I error rate and statistical power were empirically estimated for several pairwise multiple comparison strategies for situations where population variances differ. Focus was on comparing modified Bonferroni procedures with Dunnett's solutions, and determining whether or not J. P. Shaffer's suggestion of using the omnibus test would work when population variances differed. Three factors were manipulated: sample size, variance heterogeneity, and pattern of population mean differences. Twenty-four different combinations of sample sizes and variance patterns were examined for the single factor four group design. The results indicate that all eight contrast procedures considered controlled the familywise Type I error rate under the nominal 0.05 level. In terms of statistical power, the Games-Howell procedure generally provided the greater power in identifying at least one significant difference. However, the magnitude of the any-pair power difference was very small. J. P. Shaffer's (1979) enhancements to the Bonferroni approach provided greater average power per contrast as well as the greatest power in identifying all significant pairwise differences. The results of the present study indicate that previous recommendations concerning the selection of a multiple comparison procedure when population variances differ should be reconsidered, and the adoption of the new strategies for multiple comparisons is recommended. Twelve data tables and a 22-item list of references are included. (Author/RLC)

1Boy Crusoe

By Allan Eric

Also published as" A Yankee Crusoe" . A 15 year old hard working and studious farm boy finds the lure of adventure on the seas as a merchant seaman more than he can resist. This is his story. " I was born in a little town in the State of Maine, near the close of the Civil War. My boyhood life did not differ materially from that of the average farmer's son in the remote country districts of New England--except, perhaps, that I read more and thought more. Hard work on the rugged soil, two terms each year in the little yellow country schoolhouse, a day's fishing now and then filled the early years of my life full to over-flowing. " What he gets is enough excitement and adventure to overflow his wildest dreams. How he experiences disaster and uses his wits and knowledge to overcome every problem makes for a great read. - Summary by Phil Chenevert