I figured it would be fun to make a Shiny app that plots different analytical adjustments to the coefficient of determination, or R2, at different effect sizes, sample sizes, and number of predictors.
There's some discussion on this topic over at StackExchange, see e.g. here, here and here.
I used formulas from Walker, D. A. (2007). A Comparison of Eight Shrinkage Formulas under Extreme Conditions. Journal of Modern Applied Statistical Methods, 6(1), available here.
The app is hosted here.