I have created a Shiny app to calculate the required sample size for a two-group linear mixed model.

It uses the `power.mmrm`

function from the `longpower`

package (see Lu, Luo, & Chen, 2008, for more information).

The input is simplified, whereby users are limited to five time-points, the correlation matrix is a compound symmetry correlation structure that is identical for both groups, and the attrition rate is assumed to be the same for both groups.

# Shiny App

https://sammancuso.shinyapps.io/power/

# Code

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