1. What makes an experiment “fair”?
Write this in your notebook as your heading
Variables
What makes an experiment “fair”?

2. A variable is something that changes in an experiment
Write this in your notebook as your heading
Variables
A variable is something that changes in an experiment

3. Science experiments use…
Independent Variable (manipulated): the one and only factor that is changed in an experiment.
Dependent Variable(responding): the factor which is measured/observed in the experiment. Responds to changes in the independent variable.
Controlled variables (constants): all the factors that stay the same in an experiment
Write this in your notebook

4. An 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.
Yes, also write this. You will thank me later

5. Variables Independent Variable: color of the feeders
Dependent Variable: amount of seed eaten/number of birds
Controlled (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

6. Our Experimental Design
Create and fill out this data table in your notes
Our Experimental Design
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Controlled variables
Location of feeders
Kind of seed
Type of feeder
Independent
Variable
Red
Blue
Green
Dependent
Amount of Seed Eaten/number of birds

7. 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!)

8. 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?

9. Why is it important to change only 1 thing at a time?
Collect answers…

10. If you don’t… then you won’t know what is causing your results.
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

11. 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.
Talk with your group and determine the following:
Independent variable
Dependent variable
Controlled variables (constants)

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

13. Terry’s Experimental Design
Independent
Variable
Kind of seed:
Expensive feed
Cheap feed
Dependent
Number 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