Statistical Power Guidelines

Are there standard guidelines used for choice of statistical power?  This really depends on the situation and the business, safety, customer, and other risks associated with Type 2 error.

Having offered this disclaimer, here are some thoughts that might provide a useful starting point for the discussion.

In the absence of an informed decision based on business risk it may be useful to start with the following suggestions:
  • For safety-critical issues, a statistical power no less than 90% might be appropriate. (Type 2 error of no greater than 10%.) Perhaps higher if warranted.
  • For standard business/engineering applications a statistical power no less than 80% is sometimes used. (Type 2 error of no greater than 20%.)
  • For those who suggest that even lower statistical power is OK, this begs the question as to whether or not the testing is a good use of business resources.
Of course if the testing is performed with smaller sample sizes (and lower statistical power) but from the testing a statistically significant difference IS found, then Type 2 error is no longer an issue.


The choice of statistical power depends on the business situation as noted above and is the decision of those sponsoring the study, who should seek advice from a statistician who works with the statistical methods that will be employed.