Originally Posted by

**newbie2008** I am trying to calculate some t-test results for a rather large dataset. The dataset has been log transformed because it has a positive skew. The distributions I am trying to compare are independent and are different sizes, so I am using Welch's approximation. I get the below equation:

(xbar1-xbar2)/sqrt(s1/n1)+(s2/n2)

(5.74-4.32)/sqrt((0.50/21936158)+(0.16/65008))

where xbar is the mean of the sample, s is the variance (the square of the standard deviation), and n is the number of samples.

The variance of the log transform is obviously quite small, but the amount of samples is large. I am therefore getting a very large negative number for the t-test result. This can't be right can it? I think I must be misinterpreting one of the parameters, but I'm not sure which. When I try to calculate the degrees of freedom I get a ridiculous number too.

Thanks for any assistance