What is the difference between the t and Z statistics and when do I use each of them?

I have the equations, but i don't know which stat to use when.

What is the difference between the t and Z statistics and when do I use each of them?
(I'm remembering from a class I took a year ago so you might want to check my answer) Z statistics are used when you have a standardized standard deviation (sigma). For example if you are using a machine that has a known standard deviation associated with it. You use t statistics when you have to calculate the standard deviation (s) from the data you have.





Hope that helps
Reply:t- relates to a normal distribution on a bell curve and allows the comparison of two groups. The Z score is used to convert non-normal distributions to be able to compare two groups. They relate directly to parametric and non-parametric tests.