If you learned much about calculating power or sample sizes in your statistics classes, chances are, it was on something very, very simple, like a z-test.

But there are many design issues that affect power in a study that go way beyond a z-test. Like:

- repeated measures
- clustering of individuals
- blocking
- including covariates in a model

Regular sample size software can accommodate some of these issues, but not all. And there is just something wonderful about finding a tool that does just what you need it to.

Especially when it’s free.

Enter *Optimal Design Plus Empirical Evidence* software. [Read more…] about Sample Size Estimates for Multilevel Randomized Trials