MadSci Network: Environment

Re: What does Manipulative varibles and responding varibles mean exactly please

Date: Thu Jan 25 22:23:28 2001
Posted By: Eric Maass, Director, semiconductors / communication products
Area of science: Environment
ID: 980394485.En

Hello, Tiffany.  When I was in school, I also sometimes had trouble 
understanding what the different scientific words 
were supposed to mean.  In science,  we try to give words very precise meanings 
- and when we do, we often make 
even simple things sound so complex that they get really, really confusing. Oh, 
well.  Let me see if I can help make 
things a bit clearer for you.

When you run an experiment, you change some things, and see what happens. That 
is what your teacher meant when 
he said something like "manipulative variables mean change".  

The word "manipulate" means to control something.  So, a manipulative variable 
is a variable that you control by 
changing it.  For example, if your experiment is to make pancakes and see how 
good they taste, you might change how 
much milk you add in the recipe - so, the amount of milk would be your 
manipulative variable.  You might compare one 
batch of pancakes where you followed the recipe on the pancake box exactly:  

1 cup of pancake mix, 1 cup of milk, 1 egg, cook at medium.....
                 .....and another batch where you just changed the amount of 
1 cup of pancake mix, 2 cups of milk, 1 egg, cook at medium.

Now - here is the confusing part, and probably the reason your teacher said that 
"manipulative variables mean change", 
rather than "manipulative variables are the ones you control" 
....ready? comes the confusing part...

             After you changed the amount of milk in your pancake experiment, 
	      you compared the pancakes where you changed the amount of milk, 
             to the pancakes you make where you don't change the amount of 

             and we often call the pancakes we didn't change anything on (made 
following the recipe on the box)
                             ...."the CONTROL group"!

             So, your teacher didn't want to call the manipulative variable 
"something you control" 
             because...well, that might confuse you later when you learn about 
              control groups where nothing is changed.  

Yep, we sometimes make things very confusing. 

Also...well, there are many variables you could have changed in your pancake 
experiment. You could have changed how 
much pancake mix you added, or how many eggs you added, or what temperature you 
cooked at. All of these are 
controlling variables that you could have changed.  

But, you decided to only change the amount of milk - so milk is the only 
manipulative variable, the only variable you 
changed in your experiment.

Now, suppose you had decided instead to have several different batters you tried 
in your pancake experiment - one 
control group where you followed the recipe:

1 cup of pancake mix, 1 cup of milk, 1 egg, cook at medium.....

           ...and a second set of pancakes where you changed how many eggs:
1 cup of pancake mix, 1 cup of milk, 2 eggs, cook at medium.....

          .... and a third set of pancakes where you changed the heat:
1 cup of pancake mix, 1 cup of milk, 1 egg, cook at low .....

Now, you have two manipulative variables: eggs and heat.  You left the amount of 
milk and the amount of pancake mix 
constant, rather than manipulating them.  

I hope that makes sense. If you need further help, here's a webpage that 
explains this further:

Complex Science Processes: Definitions and Indicators

Responding variables are what you look at to see the results of what you 
manipulated.  In the pancake example, your 
responding variable might be how high the pancakes rise. Maybe the pancakes that 
you made with 2 cups of milk are 
really flat while the control group pancakes are nice and fluffy - that 
fluffiness is the result, the responding variable. 
Or, maybe you had 3 friends taste one pancake from each group and give a rating 
from 0 to 10 on how good it tasted, 
and you added up their ratings.  

Following the recipe on the box, the pancakes in the control group got rated a 7 
by Jeannie, an 8 by Paul, and a 10 by 
Freddie who loves pancakes.  Adding these up, the control group got a taste 
score of 7 + 8 + 10 = 25.

In the group where you manipulated the amount of milk and used twice as much 
milk, the pancakes got rated a 5 by 
Jeannie, a 2 by Paul, and a 10 by Freddie who loves pancakes no matter how flat 
or runny they are. 

So, while the control group got a taste score of 25, and the pancakes with two 
cups of milk used got a taste score of 
17. The taste score is the responding variable - it is the result that is 
affected by the variable you manipulated.

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