Optimal Design

How do you know when to use a time series and when to use a linear mixed model for longitudinal data?

What’s the difference between repeated measures data and longitudinal?
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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. (more…)

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