I have a problem. Our experiment lasts about 2 hours, as a result of which we decided to divide it into several subexperiments. But now there is a question of how to compare events from different parts of the experiment using contrast. In the first part of the experiment there were 9 events , in the second half of the experiment there were 4 . The name of all 13 events is different, tell me how can I calculate the contrast for the events from the first half of the experiment and the event from the second half of the experiment?