Manipulated and Responding Variables

Date: 01/13/2002 at 15:59:11
From: Katie
Subject: Variables

What are manipulated variables and responding variables?

Date: 01/14/2002 at 14:17:27
From: Doctor Achilles
Subject: Re: Variables

Hi Katie,

Thanks for writing to Dr. Math.

Let's say I'm doing some sort of scientific study. The manipulated 
variable is what I change, and I see how the responding variable 
reacts.

Here are a few examples:

1) In physics. I want to see how the time to go a fixed distance 
changes with speed. So what I do is I have a 1 mile course. I send one 
car down the course at 5 miles per hour, one car at 20 miles per hour, 
and one car at 60 miles per hour. So the thing that I am messing 
around with (or "manipulating") is the speed. The thing that I'm 
measuring (i.e. measuring its response) is the time.

2) In politics. I want to see how age relates to voting behavior. So I 
survey a thousand people who are between 20 and 30, a thousand people 
who are between 30 and 50, and a thousand people who are over 50. I 
then see what percentage of each group votes regularly. So the 
variable that I'm messing with (or manipulating) is age. And the 
variable that I'm measuring the response of is percentage who vote.

I hope this helps. If you have other questions about this or you're 
still stuck, please write back. If you'd like more help, I can 
probably give you a more specific answer if you write back with a 
problem or two that you've been stuck on.

- Doctor Achilles, The Math Forum
  http://mathforum.org/dr.math/