Student's t-Test
Message posted by Jane on July 7, 2000 at 12:00 AM (ET)

I am illiterate when it comes to stats. However, I have a thesis to finish and need help!!
I have two groups of mice that are being fed different diets and I am using an unpaired Student's t-Test to compare their weights. An online calculator figured out all the details and returned these results to me:
"t=0.528 sdev=3.76
degrees of freedom=51
The probablility of this result, assuming the null hypothesis, is 0.600"

What does that tell me? Can anyone explain?

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Re: Student's t-Test
Message posted by Phil on July 7, 2000 at 12:00 AM (ET)

Your results (small t-statistic) shows that you "cannot reject the null hypothesis" and you conclude that the diets had no significant effect on the weight.

The 0.60 is a "p-value". That is what the level of "Type I error" (alpha) would have to be before you would have rejected the null hypothesis in favor of the alternative.

So, if you were hoping the two diets would produce different weights, your data did not show that at all.

Re: Student's t-Test
Message posted by Phil on July 7, 2000 at 12:00 AM (ET)

If you have the beginning weights for each subject, you could also consider doing an "analysis of covariance". This analysis would remove any influence of higher or lower starting weights. It could be that by correcting for starting weight you could get a significant difference after all.