Statistical significance and decision–making
One of the defences of the use of traditional “null hypothesis significance testing” (NHST) in clinical trials is that, at some point, it is necessary to make a decision about whether a treatment should be used, and “statistical significance” gives us a way of doing that. I hear versions of this argument on a regular basis.
But the argument has always seemed to me to be ridiculous. Even if significance tests could tell you that the null hypothesis was wrong (they can’t), that doesn’t give you any basis for a sensible decision. A null hypothesis being wrong doesn’t tell you whether the treatment has a big enough effect to be worth implementing, and it takes no account of other important things, like cost-effectiveness, safety, feasibility or patient acceptability. Not a good basis for what are potentially life and death decisions.
But don’t listen to me: listen to The American Statistical Association. Their Statement on Statistical Significance and P-Values from earlier this year addresses exactly this point. The third of their principles is:
“Scientific conclusions and business or policy decisions should not be based only on whether a p-value passes a specific threshold.”
Pretty unambiguous, I think.