I am interested in making some graphs to portray 4 different research
designs:  Randomized experiment, regression discontinuity design,
instrumental variable design and matching on observables design.  These are
all economic models.  Basically, all I need is just conceptual graphs to make
it easier to understand the theory behind them.  So, I don't have any data
available.  Would anyone know how I could do that in excel.  I appreciate
your time and help very much.  Look forward to hearing from you.  

Sincerely,

Ledi