null hypothesis

A statement about statistical data set up by the investigator to allow statistical testing of an aspect of the data. The null hypothesis is often the opposite of what the investigator believes to be true, but is put forward in the hope that the data will contradict it. When this happens the null hypothesis is rejected and the alternative hypothesis (usually what the investigator is interested in showing) is understood to be supported by the data. This rather tortuous approach is favored because it avoids the logical problem of assuming the truth of a hypothesis on the basis of one measurement or set of measurements (since there is no logical way to be certain that measuring again wouldn't give a different answer).