Question 527512
What if it turns out that there is really no difference between the mean self-esteem scores of black students who attend HBCUs and all black students? What kind of error have we made? 

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The Ho would have to be:
Ho: u1-u2 = 0
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The only error you could make would be to reject Ho.
That is a Type I error.
Cheers,
Stan H.