1. While we assumed that the above experiment is flawless to answer Q1-3, the experiment is in fact subject to a critical error. If shoppers of store A innately consume more cereals than the shoppers of store B (perhaps shoppers of store A have a large family on average), it is possible that the 0.5 box difference per shopping trip (1 box from Store A 0.5 box from Store B) may result from the difference in the shoppers innate consumption habit not from the difference in package design. In this case, the experimental results in Q1 loses internal validity because the difference in sales results not from the difference in package design. You can resolve this issue by applying the two-group before-after design. Refer to the Week 3 lecture about the schema of the two-group before-after design to answer the following questions.

2-1) What should be EG, CG, O1, O2, O3, O4, and X (10 points)

2-2) Suppose that O2 and O4 are 1 box and 0.5 box, respectively (same as in Q1). Suppose further than O1 is 0.9 box and O3 is 0.2 box. Does it make sense to replace the current package with the new one? Show your computation (20 points) (Hint: In a two-group before-after design, the effect of new package is computed as (O2 O1) (O4 O3) )