A research team is studying the effects of a new energy drink on athletic performance. One researcher, who believes the drink is highly effective, is responsible for timing the athletes' sprints. This researcher is aware of which athletes consumed the new drink and which consumed a placebo. The results show that the athletes who consumed the new drink had significantly faster sprint times. Which of the following describes the most likely threat to the validity of this study's conclusion?

Double-Blind Study

Single-Blind Study

In a ______ experiment, both the researchers and the participants are kept unaware of which condition each participant has been assigned to.