R help - Apr 2017 - difference-in-difference method for estimating causal impact,

Hello, 

i want to estimate the causal impact on a scale variable, using the
difference-in-difference-method and the following 4 groups
- control- and treatment group (counterfactual analysis) 
- two periods, measurement before and after treatment.? 

After discovering and estimating the causal effect (of course, only if existing)
i like to make deeper analysis, causal mediation analysis, and fixed effects
analyisis.??

Does anyone know a package or packages, with which one can do this estimations,
calculation and graphics?
Thanks a? lot for any information.
iksmax


   
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