6.1 A Quick Introduction

Let’s consider that there are two groups: group \(i)\) receives the treatment and group \(ii)\) does not receive the treatment. We term group \(i)\) as the treatment group and group \(ii)\) as the control or untreated group. We want to compare the two groups in the pre-treatment period versus the post-treatment period. While doing so we will be utilizing both within and across variation in outcomes between the two groups.