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Short answer: It is not posible to have "significant factor effect while there is no significant difference between the two factor level means." If the equations 'exactly equivalent,' which they are, then when you reject the null hypothesis with one of them, you will reject it with the other, as well.


Try some sample data, and see how it comes out.

Cheers,
Jay

Gang Chen wrote:

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Suppose there is one factor with two levels. I could either run one-way
ANOVA or unpaired t test. I always thought that the unpaired t-test would be
the same as one-way ANOVA in the following sense: the F test in ANOVA for
two factor level means being equal (or factor effect) would be equivalent to
the unpaired t test for the difference betwen the two factor level means
since F = t^2 holds in this case.

After I took a close look of the formulas, I now realize that unpaired t
test is exactly equivalent to a one-way ANOVA when the latter is used to
test for a difference in means between two factor levels. Then I have
problem understanding the subtle difference: It seems that it is possible to
have significant factor effect while there is no significant difference
between the two factor level means. My question is: How is this possible?

Thanks,
Gang Chen






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