Professor Yarnofsky Wonders Whether Recent Acts of Airline Terrorism Have

Professor Yarnofsky wonders whether recent acts of airline terrorism have made the public more fearful of airline flight.He secures records of the number of times passengers have cancelled their travel plans within 3 days of flying,and compares the cancellation rates before the last hijacking to cancellation rates after the last hijacking.Professor Yarnofsky has employed a(n) ________ research method.

A) correlational
B) participant observation
C) archival
D) systematic observation
E) experimental