A student wants to know if a bicycle will stop faster with the hand brake or the foot brake. To investigate, she will have a friend ride the bicycle 30 times at full speed. In half of the rides, the hand break will be applied, and in the other half the foot break will be applied. For each of the 30 trials, she will measure the distance it takes the bicycle to come to a complete stop. Which of the following determines the treatments in this study?

(A) The brand of bicycle
(B) The distance it takes to stop
(C) The speed of the bicycle
(D) The type of braking used


Correct answer and commentary

The correct answer to this item is choice (D). The student wants to know which type of brake will stop the bike faster. In an experiment, as many variables as possible must be the same for all trials, with the exception of the variable that the student is interested in. The variable that is different between trials is the treatment. Therefore, in this experiment, the treatments are determined by the type of braking used (hand brake or foot brake).

About 33% of students answered this item correctly. Only 7% of students selected choice (A). This choice is incorrect because the variable of interest is not the type of bicycle, but the type of braking that will be used. The brand of bicycle would be important if the student was interested in, for example, which brand of bike stops the fastest using the foot brake. Choice (C) was selected by 27% of the students. The speed of the bicycle is an important factor in braking distance, however, the student attempted to ride the bicycle at “full speed” in each of the trials. Therefore, this variable is held constant and does not determine the treatments in the study. Choice (B) was actually the most popular of all the answers to this item with slightly over 33% of students selecting it. The distance it takes to stop is the variable that will be recorded in the experiment and will be used to determine which type of braking will stop faster, however, it is not the variable that is systematically changed in this study, which is the one that determines the treatments.

Student performance