In other words, if, through the test of the research hypothesis, we find a difference and calculate that the likelihood of that difference occurring by chance is somewhat extreme, then the research hypothesis is a more attractive explanation than the null. So, if we find a z score (and remember that z scores have probabilities of occurrence associated with them as well) that is extreme (how extreme?—less than a 5% chance of occurring), we like to say that the reason for the extreme score is something to do with treatments or relationships or a real difference between groups
