MadSci Network: Environment Query:

### 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
Message:
```
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
milk:
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?...Okay...here 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
milk.....

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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