FAQ/powposi - CBU statistics Wiki

Upload page content

You can upload content for the page named below. If you change the page name, you can also upload content for another page. If the page name is empty, we derive the page name from the file name.

File to load page content from
Page name
WHat wOrd is made by the captiaL lettErs?

location: FAQ / powposi

A quick method for performing power analyses on Poisson counts

[From Thom Baguley]

More in Thom's book at https://seriousstats.wordpress.com/2012/02/. Chapter 17 focuses on generalized linear models (mainly Poisson and logistic regression).

As far as a quick and dirty sample size calculation goes you could take the square root of the counts and use a normal approximation* (i.e., the method that you'd use for regular ANOVA or t tests). For anything fancy it is more elegant to use simulation - but there will not be much gain from the quick and dirty approach unless you have a lot of information about the problem.

* The Poisson distribution has a single parameter that is both mean and variance - the square root transformation is well known as a (very) approximate normalizing transformation in this case.