Quote:
In Reply to Parent Post by jackylpt
As Homogeneity of Varirance( Mintab) can test normal and nonnormal data for variance.
My question is does t test can do it? if not, how we can compare two nonnormal data mean value? thanks

Yes, the ttest is based upon an assumption of normality. If you are concerned about the normality of your data, here are some options:
1. Assume the Central Limit Theorm will get you to "good enough". Generally if you have more than 10 samples you probably are getting close.
2. Ignore the issue. With only 5 samples (for example) it is pretty hard to prove your data are not normal anyway.
3. If you know what distribtution the data are, or theoretically "ought to be", run a mathematical transform to shift them to normality. An example is time to failure data can tend to be exponential.
4. Run your own tests using random numbers and check distributions like what you have been seeing to see how good the ttest is at avoiding false alarms and avoiding failure to detects.
5. Shift to nonParametric tests.