Why is Loftus and Palmer's (1974) study considered a laboratory experiment?

Loftus and Palmer's study is considered a laboratory experiment as the independent variable was manipulated. A laboratory experiment examines the causal relationship between the independent variable (IV), a factor the researchers change, and the dependent variable (DV), a factor the researchers measure. In Loftus and Palmer's study the independent variable was the verb used in the critical question ‘about how fast were the cars going when they _____ each other?’. The blank space was filled with either the verb smashed, collided, bumped, hit or contacted. Loftus and Palmer were investigating how the verb used in this question might affect the speed estimates participants gave after watching clips of car crashes. The speed estimates were therefore the DV for this experiment. This experiment was also followed by another where the same question was used but with only the verbs hit and smashed. The DV was also different as it was the number of participants who stated, a week after viewing the video and being asked to provide a speed estimate, that they saw broken glass at the scene of the crash. As a result, Loftus and Palmer's study is considered a laboratory experiment due to the fact that researchers manipulated and measured variables in an artificial environment, in this case to examine how leading questions may affect eyewitness testimony.