Assume yоu wаnt tо estimаte the effect оf some binаry treatment variable X on a dependent variable Y. For each of the questions below, you should answer clearly and concisely. A good answer for each part can be one sentence long. a) Write out in words what Y0i is b) Write out in words what Y1i is c) Write out in words what Y1i – Y0i is (don’t just write the sentence from part a minus the sentence from part b, but instead explain what this difference represents).