The Beck depression inventory is used by this researcher in order to determine the effectiveness of the drug treatment. The BDI has a test-retest reliability of .86 which can be taken to mean what? People who score high on test one will show an 86% probability of improvement following an effective treatment, 86% of people who take the test at time one will show the same score at two, score at first testing, and then again at the retesting correlate highly (r = .86), there is no significant difference between testings (p = .86)