Hi Olivia, I have several questions. Can we use Zelig this time? As for #2(a), should we include not only the treatment indicator but also intercept, too? As for #2(c), if we fit separate regressions for control and treatment, treatment can not be an independent variable? I'm afraid I misunderstand the problem, but could you give me any hint? How can we output R data frame into another format such as csv? Thank you in advance. Kentaro