2

Can someone clarify this:

My text states: If the computed p-value is less than or equal to alpha, reject the null .... If the computed p-value is greater than alpha, then fail to reject the null ...

But the software accompanying the text states: Is the p-value less than the level of significance? If yes, reject the null hypothesis .... If no, fail to reject the null hypothesis ....

Which is correct? If I go by prior discussions in the text where we use z and z_critical to make a decision, the rule was to reject the null if z > |z-critical|. If z exceeds |z-critical| then the corresponding p-value (for z) must be smaller than the corresponding alpha value (for z-critical) to reject the Null. So the z > |z-critical| rule agrees with what the software says about using p values. So, is the rule stated in the text incorrect? Is the software incorrect? Or, am I wrong in my reasoning? Thanks.

VGR
  • 21

1 Answers1

0

Those statements do agree. The text statement says that if (and only if) the computed $p$-value is less than some level ($\alpha$, which might be say 5%) then reject the null hypothesis. Of course, this rejection happens when the $z$ quantity is greater than some critical $z$ which depends on your selected $\alpha$.

The software statement is that if $p$ is less than the level of significance (which would be that same 5%) then yes, reject the null hypothesis; if not, then fail to reject. This is exactly the same as the text statement.

Mark Fischler
  • 41,743
  • Mark: The text statement says "less than or equal to" and not "less than." The software says "less than" and not "less than or equal to." So, how do the two statements agree? –  Apr 18 '15 at 02:01