ExplanationWhat a Paired T-Test Does
A paired t-test compares two samples in cases where each value in one sample has a natural partner in the other. The concept of paired samples is covered in more detail in the pages on choosing a t-test.
What a Paired T-Test Measures
A paired t-test looks at the difference between paired values in two samples, takes into account the variation of values within each sample, and produces a single number known as a t-value.
You can find out how likely it is that two samples from the same population (i.e where there should be no difference) would produce a t-value as big, or bigger, than yours. This value is called a p-value. So, a t-test measures how different two samples are (the t-value) and tells you how likely it is that such a difference would appear in two samples from the same population (the p-value). P-values and t-values are covered in more detail in the next topic.
How to use a Paired T-Test
This level assumes that you will use a software package to perform a t-test. If you want to know how to do it by hand, read level two.
Software can perform the calculations to produce t-values and p-values, but it is your responsibility to do the following:
- Pick the right kind of t-test, in this case, a paired t-test and the right direction of test (one or two tailed). See the pages on choosing a t-test for more on this;
- Ensure the distribution of your data is suitable for a t-test. See the pages on the normal distribution for more on this;
- Know how to interpret the results of doing a t-test. See the pages on t-values and p-values for more on this.
One final practical point: each value in one sample is paired with a single value in the other. When you enter your data into a computer for analysis by a software package, make sure the paired values are lined up. This usually means having data in two columns where each row represents a single pair. The fact that values are paired is very important.