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In experimental design, explanatory variables are the factors that researchers manipulate to observe how they affect the outcome of an experiment. They are sometimes referred to as independent variables because they are independent of other variables in the experiment. In the exercise mentioned, there are two explanatory variables: the height of the step, which can be either 5.75 inches or 11.5 inches, and the speed indicated by the metronome beat, which is varied at 14, 21, or 28 steps per minute.
By changing these variables, the experimenters aim to see how different combinations impact the heart rate increase in students. This allows researchers to identify which specific conditions lead to the biggest changes in heart rate.

• The height of the step: 5.75 inches or 11.5 inches
• The metronome beat: 14, 21, or 28 steps per minute

These variables are fundamental to any experimental setup as they guide the framework of how the experiment is conducted.

Response variables, often called dependent variables, are the outcomes that researchers measure in an experiment to determine the effect of the explanatory variables. They provide critical insights into the research question by showing the changes or results of applying different treatments.
In the student project exercise, the response variable is the increase in heart rate of the students after stepping up and down for a set period. This is the variable of interest as it reflects how the different step heights and metronome speeds affect the heart rates of participants.
Heart rate is a quantifiable and objective measure, making it an ideal response variable for this study. By analyzing the changes in response variables under different conditions, it becomes possible to draw conclusions about the effects of the treatments.

Experimental units are the subjects or entities involved in an experiment on which the explanatory variables are applied. They are the physical units of observation, which in this study are the students who participate and have their heart rates measured.
Each student is exposed to specific treatments, such as a particular step height and metronome speed, to observe how their heart rate responds.

• In this study, the experimental units are the fellow students.
• Each student's reaction to different treatments is recorded to compare results.

By using multiple students, the researchers can account for variability in responses and ensure that the results are more generalized and not merely due to individual differences. It is crucial to select experimental units carefully, as they significantly influence the reliability and validity of the experiment.

Treatments in an experiment are the specific conditions applied to experimental units, involving different levels of the explanatory variables. In this student project, the treatments are combinations of step heights and metronome speeds.
Each treatment is a unique combination of a step height and a metronome speed, resulting in a total of six distinct treatment scenarios that students are subjected to. For example, a treatment could be stepping at 5.75 inches high with a metronome speed of 14 steps per minute.

• 5.75 inch step combined with 14, 21, or 28 steps per minute
• 11.5 inch step combined with 14, 21, or 28 steps per minute

Altogether, these combinations allow the experiment to explore how each set of conditions affects the outcome, providing comprehensive insights into which factors most strongly influence heart rate changes. Accurate treatment application is essential to identify the relationship between explanatory variables and response variables.