# Undetermined power & retrospective study

My question is about a retrospective medical study in which no significant difference was found between two different treatments. What exactly is meant by "the lack of a significant difference does not imply equivalence because of the undetermined power of statistical tests"?

• I agree with the theoretical correctness of the above. However, there is strict equivalence, i.e, mean = 0, and there is practical equivalence, mean = 0 $\pm$ some amount considered insignificant. The latter type of equivalence can be addressed with a sufficiently powered test. – user31668 Dec 16 '13 at 15:52