Question

The residential division of Seeger Inc. high speed Internet service uses one advertising agency while its commercial division uses another. Two analysts, are asked to test evaluate effectiveness of the two agencies. Howard proposes an H/C test that compares the click-through rates per ad for the two agencies. Carol proposes a difference-in-difference test in which the budgets for both agencies are increased by 50% and the percent change in click-through rates are compared.

What might be the sources of selection bias for the two proposals?

Which is likely to be smaller?

Answer 1