### ExplanationThe paired t-test is calculated to take into account the fact that pairs of subjects (one from each condition) go together. It is based on the differences between the values of each pair - that is one subtracted from the other. In the formula for a paired t-test, this difference is notated as *d*.When you look at the formula for the paired t-test below, you will see that it uses just d and n (the number of values in the data), and nothing else. The way these two values effect the value of t are as follows: - As the average of the differences gets bigger, t gets bigger;
- As the variation in the differences gets bigger, t gets smaller;
- As the number of values gets bigger, t gets bigger.
There is another way of writing the paired t-test formula, that you might see in a book. It makes the above points clearer, but is not so easy to use to calculate a t-value from data. It is shown in the help topic below if you are interested in seeing it. |