In plotting the relationship between the incidence of breast cancer and the level of vitamin D in the body, we would most likely plot
A) vitamin D on the Y axis and incidence of breast cancer on the X axis.
B) average daily sunlight on the Y axis and the incidence of breast cancer on the X axis.
C) vitamin D on the X axis and incidence of breast cancer on the Y axis.
D) The three answers above are equally good.

Question

Quizplus · Accepted Answer

Vitamin D is the independent variable being studied (i.e. the variable that could potentially influence the incidence of breast cancer), and thus is usually plotted on the X axis. The incidence of breast cancer is the dependent variable (i.e. the variable that could potentially be influenced by vitamin D levels), and is usually plotted on the Y axis. Option C correctly reflects this relationship. Option A is incorrect because it does not follow the convention of placing the independent variable on the X axis. Option B may be a confounding variable because it is not directly related to vitamin D levels, and thus may introduce error into the study.

In Plotting the Relationship Between the Incidence of Breast Cancer