GMAT Test Prep: CR-58863384 GMAT Critical Reasoning

Because of steep increases in the average price per box of cereal over the last 10 years, overall sales of cereal have recently begun to drop. In an attempt to improve sales, one major cereal manufacturer reduced the wholesale prices of its cereals by 20 percent. Since most other cereal manufacturers have announced that they will follow suit, it is likely that the level of overall sales of cereal will rise significantly.

Which of the following would it be most useful to establish in evaluating the argument?