Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A test method is a definitive procedure that produces a test result. The test result can be qualitative, categorical, or quantitative. It can be a personal observation or the output of a precision measuring instrument. Usually the test result is the dependent variable, the measured response based on the particular conditions of the test or the level of the independent variable. Some tests, however, involve changing the independent variable to determine the level at which a certain response occurs: in this case, the test result is the independent variable.