1. designing an
experiment

2. A variable is something that changes.

3. 4 concepts of experimental design
independent variable
dependent variable
Constants/control
repeated trials
© 2004 Plano ISD, Plano, TX

4. the variable that is changed on purpose by the experimenter
independent variable
the variable that is changed on purpose by the experimenter
aka cause, stimulus, reason, manipulated variable, etc.
This is the ‘’if” part of a hypothesis.

5. the variable that responds
dependent variable
the variable that responds
aka effect(s), result(s), responding variable, etc.
This is the ‘’then” part of a hypothesis.

6. all factors which are NOT allowed to change during the experiment
constants
all factors which are NOT allowed to change during the experiment

7. the group (standard) to which everything is compared
control group
the group (standard) to which everything is compared

8. the number of times the experiment is repeated
repeated trials
the number of times the experiment is repeated
The more times you repeat the experiment, the more VALID your results are.

9. 6 drops fertilizer
4 drops fertilizer
2 drops fertilizer
no fertilizer

10. EXPERIMENTAL GROUP CONTROL 2 drops fertilizer 4 drops fertilizer
What is this called?
What are these called?
CONTROL
EXPERIMENTAL GROUP
no fertilizer

11. What are these called?
CONSTANTS

12. dependent variable What is this called?
The plant growth that you observe here can be called . . .
 the results (of adding fertilizer)
 the response (to adding fertilizer)
dependent variable
 the effects (of adding fertilizer) 2 4 6

13. These are the fertilizer amounts varied by the experimenter.iv
constants dv
fertilizer
The variable (factor) that you will change is the independent variable.
0 drops
These are the fertilizer amounts varied by the experimenter.
2 drops
4 drops
6 drops

14. iv
constants dv
fertilizer
plant growth
0 drops
The variable (factor) resulting from the independent variable is the dependent variable.
2 drops
4 drops
6 drops

15. iv
constants dv
fertilizer
amt. of water
plant growth
type of soil
0 drops
These are the factors that must NOT change during experimentation. They must remain constant.
amt. of soil
2 drops
type of plant
4 drops
type of planter
6 drops
size of planter
type of light
location

16. Type of soil becomes the IV.
What do you do if you want to test the type of soil instead of fertilizer? iv dv
constants
plant growth
fertilizer
amt. of water
type of plant
type of planter
size of planter
amt. of soil
type of light
location
type of soil
type of soil
fertilizer
Type of soil becomes the IV.
Fertilizer becomes a constant.

17. In the following two slides, identify the
independent variable
constants
dependent variable.