GMAT Test Prep: CR-79005445 GMAT Critical Reasoning

A researcher studying corporate executives found that they tend to have "take charge" personalities, with the predominant traits of assertiveness, decisiveness, and self-confidence.

The researcher concluded that people who are more "take charge" than the average person are more likely to become corporate executives. Which of the following, if true, most seriously weakens the researcher's conclusion?
Select one of the following answer choices