Friday, October 15, 2010

Talk about Algebra: Independent and Dependent Variables

Today's vocabulary includes two terms: Independent Variable and Dependent Variable. When given a situation with data, students are expected to know which set is the Independent (often called Control) and which are the Dependent.

If you think of a function like a machine, the Independent Variable is the input set, and Dependent is the output. So if this were a factory, The Independent Variable would be the metal going in, and the Dependent Variable would be the cars coming out the other side.

Another example, more grounded in our lesson, is the comparison of the money we make, with hours worked. The longer you work, the more money you make. Hours is Independent, Pay is Dependent.

We do this all the time in education research. Some reserachers experiment with class sizes, comparing how many students are in a class with how well they do on standardized tests. In this case the Independent variable is the number of students, the Dependent is test scores.

In short, anything we control going in is the Independent, and the results of that is the Dependent.

Tied to this I raised a question towards the end of our lesson:

When you compare the number of stocks sold, with the value of those stocks, which is the Independent, and which is the Dependent?  In other words, which one Determines the other?  Which one is Dependent on the other?  Do sales drive price, or do prices drive sales?

Feel free to post your own answer to this in the comments.  As usual participation is worthy of Brownie Points, and please no last names.


  1. the value/amount depends on the stocks sold.


  2. The value is the dependent and the stocks sold are the independent becuase the value depends on the stocks sold, and because the value is a function of he stocks sold.

    5th hour