A proposition that is assumed to be true.  One examines outcomes (e.g., from an experiment) to see if they are consistent with the null hypothesis. Unfortunately, the null hypothesis is often selected for its convenience rather than for its truth. The rejection of an unreasonable null hypothesis (or nil hypothesis) does not advance knowledge. For example, testing against the null hypothesis that income unrelated to the sales of automobiles would be foolish at best and might even be misleading (see statistical significance). Unfortunately, null hypotheses are frequently misused in science (Hubbard and Armstrong 1992).

• Hubbard, R. & J. S. Armstrong (1992), “Are null results becoming an endangered species in marketing,” Marketing Letters, 3, 127-136. (Full text)