Dependent vs. Independent Variables

This is still a very very rough draft.

The dependent variable is the one which changes in relation to changes in the independent variable.

**Figure 1:** Variation of the mass of
Chloe (square boxes)

and Mergatroid (triangles) over twelve months.

In this example, the masses of Chloe and Mergatroid change as the months change, they change over time. The months do not change as a function of mass. That would be weird. That would be like saying, "When Chloe is 75kg it must be the 4th month."

One variable changes in relation to another.

The independent variable is the one you either control or you already know how it changes. In this example, it is assumed that you can measure time and that time is predictable. You choose to take measurements of the masses of Chloe and Mergatroid at one-month intervals. The unpredictable variable is the mass, the dependent variable. In this example you don't know what Chloe's or Mergatroid's masses will be. Presumably you want to know how their masses change as time marches on in one month intervals. You could have chosen one-year intervals or one-day intervals. But you chose one-month intervals.

What would it mean for the dependent variable to be time and the independent variable to be mass?

To do this you would predetermine what mass intervals were to be considered. Let's say you decided that you would measure what month it was at every 5kg interval. You arbitrarily chose the 5kg interval. It is independent of the time. You will record the time whenever Chloe hits some mass that is a multiple of 5kg.

That would mean that you would wait for Chloe to reach a a multiple of 5kg and then record what month and day it was.