T-test

Between group variance?

difference between pts of 2 groups after they receive the tx they were assigned to

Within group variance?

difference between individuals in same group before and after tx

what are degrees of freedom?

the number of unique pieces of information in the dataset as long as we know the mean

Degrees of freedom formula?

[(n1 - 1) + (n2 - 1)] where “n” is the number of patients in one group

When to use a one tailed t-test

When you know the direction of the difference of interest in advance. EX: Pt will get better. Lets you decide whether or not to accept or reject the null and alternative hypothesis

When to use a two tailed t-test?

When there is a possibility that the direction of the difference of interest could go either way. EX: Pt could get better or worse)

What is a two-tailed test?

A test of any difference between groups regardless of the direction of the difference.

What is a paired t-test?

same group, two different times (or twins) EX: before and after tx

What is an independent sample t-test?

difference between the mean scores of two different populations