1. Or what changes during experiments….
What are variables?
Or what changes during experiments….

2. A variable is something that is changed
Variables
A variable is something that is changed

3. Independent Variables
What is tested by the scientist
What is changed by the scientist
Also known as manipulated variables.

4. Dependent Variable What is observed What is measured
The effect caused by the independent variable.
The data
Also called responding variables

5. Controlled Variables Things that could change but don’t
Kept constant (the same) by scientists
These allow for a fair test.

6. Variables in Science Experiments
What makes an experiment “fair”?

7. Big Picture…………
Independent Variable: the one factor that is changed by the person doing the experiment
Dependent Variable: the factor which is measured in the experiment
Control: all the factors that stay the same in an experiment

8. A Birdy Example…
Imagine you want to see what color of bird feeders your local birds preferred.
Red? Blue? Green?
If a student wanted to determine whether feeder color has an effect, he might suggest, “if I put up a red, blue, and green feeder, birds will visit the green feeder more” as a hypothesis. He might speculate that the green feeder, being the most “camouflaged” or “natural” might be visited the most.

9. Our Constants and Variables
Independent Variable: color of the feeders
Dependent Variable: amount of seed eaten
Constants: everything else that is kept the same, for example:
the location of the feeders
the kind of feeder used
putting the feeders out at the same time
Independent Variable: the one factor that is changed by the person doing the experiment
Dependent Variable: the factor which is measured in the experiment
Constants: all the factors that stay the same in an experiment

10. Our Experimental Design
Constants
Location of feeders
Kind of seed
Type of feeder
Independent
Variable
Red
Blue
Green
Dependent
Amount of Seed Eaten

11. The experiment is FAIR. (ONLY the independent variable can change!)
If everything except the independent variable is held constant, we can say:
The experiment is FAIR.
(ONLY the independent variable can change!)

12. Why is it important to only change the independent variable?
Collect answers…

13. If you don’t…
If you measure a change in the dependent variable, you won’t know whether it is the independent variable that is causing the change.
Give an example: a girl wanted to know whether her dog being out in the backyard scared birds away. She thought it would, because the dog likes to bark a lot and has been known to chase little animals.
For 5 days when the dog was out, she counted for an hour.
For 5 days the dog wasn’t out, she counted for an hour.
After she collected the data, she noticed that birds are actually out MORE when the dog is in the yard. Does that surprise you?
But, what the girl didn’t think of was other things that might effect the number of birds that were out. She began thinking that maybe something else might be going on. She realized that the dog was out on sunny warm days, and not on rainy, cool days.
So, even though she found a change, how will she know if it was the dog may have had an effect? Or was it the weather?
See if kids can suggest improvements to the experiment. (i.e. making sure the weather and temperature is similar on the days she counts.)
Independent Variable

14. Is Sam’s experiment fair? YES? NO?
Read the following scenario to the students:
Sam wants to know if birds prefer one color of feeder to another. He makes three feeders out of 2-liter bottles and paints one red, one blue, and one green. He fills the feeders with the same amount of sunflower seed, and plans to keep the feeders out for one week before measuring how much seed is eaten out of each. On Tuesday, he puts each of the feeders in his back yard: the red feeder in a large dead tree, the blue feeder he sits on the doghouse, and the green one he puts in a small bushy tree.
Is Sam’s experiment fair?
NO! It isn’t fair since the locations of the feeders were very different!

15. Is Maria’s experiment fair? YES? NO?
YES! It seems fair since Maria only changed the feeder color!
Read the following scenario to the students:
Maria wants to know if birds prefer one color of feeder to another. She makes three feeders out of 2-liter bottles and paints one red, one blue, and one green. She fills each of the feeders with the same amount of mixed birdseed, and plans to keep the feeders out for 10 days before measuring how much seed is eaten from each feeder. She puts each of the feeders in the school courtyard in a small tree, hanging each at the same height.
Does Maria’s experiment seem fair?

16. Is Jessie’s experiment fair? YES? NO?
NO! It isn’t fair since the feeders are not out at the same time, and we know that the weather was quite different each time. Perhaps the number and kind of birds that visited during the weeks were different
due to the weather.
Read the following scenario to the students:
Jessie wants to know if birds prefer one color of feeder to another. She makes three feeders out of 2-liter bottles and paints one red, one blue, and one green. She fills the each of the feeders with sunflower seed. She plans to leave each feeder out for 2 days and then measure the amount of seed that the birds ate. She has one hook in her backyard the she plans to hang each of the feeders on. She puts the red feeder out on Tuesday and measures the seed 2 days later, the green feeder doesn’t go out until Saturday since it was very snowy, but she is able to measure the seed 2 days later. The weather turned rainy, but she needs to finish her experiment, so blue feeder goes out on Monday and is measured 2 days later.
Is Jessie’s experiment fair?

17. How would you advise her to find out if the expensive seed is better?
What do you think?
Terry loves birds and wants to see as many as she can in her yard. She wants to know whether she is wasting money buying an expensive mixed seed, when a cheaper brand just arrived at her local store. She wonders… will the expensive seed attract more birds to her back yard?
You may want to have students brainstorm in pairs, or conduct a group discussion.
How would you advise her to find out if the expensive seed is better?

18. Terry’s Experimental Design
Independent
Variable ?
Dependent
Constants
What is the Independent Variable?
What is the Dependent Variable?
What would you hold constant?

19. Terry’s Experimental Design
Independent
Variable
Kind of seed:
Expensive Cheap
Dependent
Number (and perhaps kinds) of birds that visit
Constants
Location of feeders
Type of feeder
Way she measures the amount of seed eaten and the way she counts birds $
What is the Independent Variable?
What is the Dependent Variable? Number of birds– also, you may want to record what KINDS visit. Maybe diversity is higher with one seed or the other!
What would you hold constant? There are other answers as well. Feel free to add to the list

20. Identify the Controls and Variables: Homer
Homer notices that his shower is
covered in a strange green slime. His
friend Barney tells him that coconut
juice will get rid of the green slime. Homer decides to check this this out by
spraying half of the shower with coconut juice.
He sprays the other half of the shower with
water. After 3 days of "treatment" there is no
change in the appearance of the green slime
on either side of the shower.

21. Identify the Controls and Variables: Homer
What was the initial observation?
Identify the-
Control Group
Independent Variable
Dependent Variable
What should Homer's conclusion be?

22. Identify the Controls and Variables: Homer
What was the initial observation?
There was green slime on the shower wall.
Identify the-
Control Group
Used water to clean shower wall.
Independent Variable
Used coconut juice to clean shower,
Dependent Variable
Reduction of green slime.
What should Homer's conclusion be?
Coconut juice is not more effective than water.

23. Identify the Controls and Variables: Smithers
Smithers thinks that a special juice will
increase the productivity of workers.
He creates two groups of 50 workers each and
assigns each group the same task (in this
case, they're supposed to staple a set of
papers). Group A is given the special juice to drink
while they work. Group B is not given the special juice.
After an hour, Smithers counts how many stacks of
papers each group has made. Group A made 1,587
stacks, Group B made 2,113 stacks.

24. Identify the Controls and Variables: Smithers
Control Group
Independent Variable
Dependent Variable
What should Smithers' conclusion be?
How could this experiment be improved?

25. Identify the Controls and Variables: Smithers
Control Group
Group without juice.
Independent Variable
Juice
Dependent Variable
Productivity
What should Smithers' conclusion be?
The juice does not increase productivity.
How could this experiment be improved?
Group B should have water as a placebo.

26. Identify the Controls and Variables: Bart
Bart believes that mice exposed to
microwaves will become extra strong (maybe
he's been reading too much Radioactive Man).
He decides to perform this experiment by
placing 10 mice in a microwave for 10
seconds. He compared these 10 mice to another 10
mice that had not been exposed. His test consisted of
a heavy block of wood that blocked the mouse food. he
found that 8 out of 10 of the microwaved mice were
able to push the block away. 7 out of 10 of the non-
microwaved mice were able to do the same.

27. Identify the Controls and Variables: Bart
Control Group
Independent Variable
Dependent Variable
What should Bart's conclusion be?
How could Bart's experiment be improved?

28. Identify the Controls and Variables: Bart
Control Group
Mice not put in the microwave.
Independent Variable
Mice placed in the microwave.
Dependent Variable
Strength of mice.
What should Bart's conclusion be?
Microwaving mice does not increase strength.
How could Bart's experiment be improved?
Use more mice.

29. Identify the Controls and Variables: Krusty
Krusty was told that a certain itching
powder was the newest best thing on the
market, it even claims to cause 50% longer
lasting itches. Interested in this product, he
buys the itching powder and compares it to
his usual product. One test subject (A) is
sprinkled with the original itching powder, and
another test subject (B) was sprinkled with the
Experimental itching powder. Subject A reported
having itches for 30 minutes. Subject B reported
to have itches for 45 minutes.

30. Identify the Controls and Variables: Krusty
Control Group
Independent Variable
Dependent Variable
Explain whether the data supports the advertisements claims about its product.

31. Identify the Controls and Variables: Krusty
Control Group
Original Itching Powder
Independent Variable
New Itching Powder
Dependent Variable
Length of time Itching Powder worked.
Explain whether the data supports the advertisements claims about its product.
This data supports the new product’s clain to last 50% longer.