[Closi]

> we can’t say there is a statistically significant effectiveness

Agreed, although to clarify and be more precise, it also doesn't prove it's not effective. It effectively says that the sample was too small to tell anything.

> (it is not significantly different from 0% effectiveness).

This statement isn't true - it means that they are 95% sure the range of possible values is between -50 and +60, but it does not mean that the average of those two values is correct. 0% effectiveness is possible, but was not shown in this study.

[willj]

You’re right, semantics are everything. I left implicit the “in this study” part. As always, failing to reject the null doesn’t mean the null is true :)