The article shows that two active dispersion effects may create a serious dispersion effect in their interaction column,and the existing methods for dispersion-effect testing in unreplicated 2~k-p are subject to those spurious effects. The exact dispersion-effect test (D~BH test),developed by Bergman and Hynen (Ref. 1),is biased in the presence of multiple dispersion effects. The authors illustrate by conducting simulation studies that the F~ML test has many desirable properties lacking in other tests.If two active dispersion effects occur in columns that are not in the adapted location model,F~ML is biased for their interaction column only but no other.Also,unidentified location effects though create bias for both D~BH and F~ML tests,F~ML seems less susceptible.(23 refs.)
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