Null hypothesis
In inferential statistics the null hypothesis usually refers to a general statement or default position that there is no relationship between measured phenomena, or no difference among groups.
The concept of a null hypothesis is used differently in two approaches to Statistical inference. In the significance testing approach, a null hypothesis is rejected on the basis of data that is significantly unlikely if the null is true, but the null hypothesis is never accepted or proved. This is analogous to a criminal trial, in which the defendant is assumed to be innocaent (null is not rejected) until proven guilty (null is rejected) beyond a reasonable double.