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How to do the t-test

We have two groups and we want to figure out the likelihood of being correct. Are these two groups identical?

1. Calculate the difference in the means
We use eqn 2.1 to calculate and and subtract, getting .
2. Calculate the estimated variance of this difference
We use eqn. 2.11 to do get .
3. Form t
.
3. Calculate likelihood
The number of degrees of freedom , is one less than the total number of data points, that is it equals . With that and t, we feed it into a program, or use a table to calculate the area under the curve as pictured in fig. 2.7.
4. Verdict
If this area is less than our cutoff for significance, say we reject and say the difference is statistically significant. Otherwise, we can't reject .

Keywords

• how to figure probability problems.

josh 2010-10-20