The Null Hypothesis

A good quote to remember:

Research reports in the literature are frequently flawed by conclusions that state or imply that the null hypothesis is true. For example, following the finding that the difference between two sample means is not statistically significant, instead of properly concluding from this failure to reject the null hypothesis that the data do not warrant the conclusion that the population means differ, the writer concludes, at least implicitly, that there is no difference. The latter conclusion is always strictly invalid. Jacob Cohen. 1988. Statistical power analysis for the behavioral sciences. 2d ed. Hillsdale, NJ: Lawrence Erlbaum. p. 16