I am trying different methods for propensity score matching, and I have an issue on matching with replacement.
I use standardized difference to measure the "quality" of my match, and for this specific case where I can have the same control for different pairs I do not get how to compute the mean of any variable for my control group.
I know how many different control observation are used to form the pairs and the number of times each control is used to form a pair. I heard it has something to do with weighted mean, but I do not get how/why.
count the number of time each control is used to form a pair
The mean of case group a is just (70+60+90)/3 (if I am not mistaken) But what about the mean (and variance) of the control group.
Thank you for your help.