# Statistics: Power

## Rough notes on power analysis

From a message from Michael Friendly, Nov. 25, 2006:

We were talking about power analysis today, and I came across this paper describing how to do them for mixed models using proc mixed in SAS. http://statistics.unl.edu/faculty/steve/802/2001/power_sas.pdf It does require that you specify the complete set of 'exemplary means' for a design.

As well, it may be useful to know that the glmpower procedure provides power analysis for designs handled by glm:

```data Exemplary;
input Variety \$ Exposure \$ HeightOrig HeightNew Weight;
datalines;
1 1 14 15 1
1 2 16 16 2
1 3 21 20 2
2 1 10 11 1
2 2 15 14 2
2 3 16 15 2
; run;

proc glmpower data=Exemplary;
class Variety Exposure;
model HeightOrig HeightNew = Variety | Exposure;
weight Weight;
contrast 'Exposure=1 vs Exposure=3' Exposure 1 0 -1;
power
stddev = 5
ntotal = 60
power = .;
run;
```

From David Flora: There's also free software made by Raudenbush and colleagues called "Optimal Design." (http://sitemaker.umich.edu/group-based/home) I've used it a little; it generates some nice power curve graphs.