More on variables for biology class

1. VARIABLES
Controls, Dependent & Independent
Variables

2. 2 Variable
Is an element, feature, or factor
that is liable to vary or change.

3. 3 Fair Test (Experiment)
 It is important for an experiment
to be a fair test.

4. 4 Fair Test (Experiment)
 Scientists use an experiment to
search for cause and effect
relationships in nature.

5. 5 Fair Test (Experiment)
 To insure an experiment is a fair
test.
 Can only change one factor at a
time.
 Must keep all other conditions the
same.

6. 6 Fair Test (Experiment)
 Designed so changes to one
item.
 Will cause something else to
vary.
 Variations should happen in a
predictable way.

7. 7 Types of Variables
An experiment usually has three
kinds of variables:
1. Independent Variable (IV)
2. Dependent Variable (DV)
3. Controlled Variable (CV) or
Control

8. Independent Variable
8
What
you
chang
e
 Is one variable changed by a scientist.
 To insure a fair test, a good experiment
has only one independent variable.
 As the scientist changes the
independent variable, he or she
observes what happens.
 There should be only one independent
variable for any valid experiment.

9. Dependent Variable (DV)
9
What
you
observ
e
 The scientist focuses his or her
observations on the DV to see how
it responds to the change made to
the IV.
 The new value of the DV is caused
by and depends on the value of the
IV.
 There can be more than one DV.

10. Controlled Variable (CV) or
Control
10
What
you
keep
the
same
 Experiments also have controlled
variables.
 Controlled variables are quantities
remaining constant
 They must be observed as carefully
as the dependent variables.

11. Variables
Rememb
er these
guides:
Questio
n
Independe
nt Variable
Dependent
Variables
Controlled
Variables
What I
change
What I
observe
What I keep the
same
What did
the scientist
change?
What did
the scientist
observe
(see)?
What was kept
the same?
11

12. Example
12
 You are a doctor working at
Kaiser. You want to test a new
drug for cancer patients who are
being treated in your hospital.
You have a good feeling that this
drug will work. You have 100
patients on which to test your
drug.

13. Variables Remember to answer these questions:
Hypothesi
s
What is
the
control
group?
What is the
experiment
al group?
Independe
nt Variable
Dependent
Variables
Controlle
d
Variables
Which
group will I
not
change
Which
group will I
change
What I
change
What I
observe
What I
keep the
same
Which
group did
not
change?
Which
group
changes?
What did
the scientist
change?
What did the
scientist
observe
(see)?
What was
kept the
same?
13

14. Example
14
 You are on the CHS football
team. You want to know if
drinking water or drinking
Gatorade during a game is more
hydrating. The team has agreed
to help you test your hypothesis
during the next 6 games.

15. Variables Remember to answer these questions:
Hypothesi
s
What is
the
control
group?
What is the
experiment
al group?
Independe
nt Variable
Dependent
Variables
Controlle
d
Variables
Which
group will I
not
change
Which
group will I
change
What I
change
What I
observe
What I
keep the
same
Which
group did
not
change?
Which
group
changes?
What did
the scientist
change?
What did the
scientist
observe
(see)?
What was
kept the
same?
15

16. Example
16
 You have heard that chewing
gum during a test can help a
student get a higher score. Your
spiffy teacher has said that you
can test your hypothesis during
the next exam.

17. Variables Remember to answer these questions:
Hypothesi
s
What is
the
control
group?
What is the
experiment
al group?
Independe
nt Variable
Dependent
Variables
Controlle
d
Variables
Which
group will I
not
change
Which
group will I
change
What I
change
What I
observe
What I
keep the
same
Which
group did
not
change?
Which
group
changes?
What did
the scientist
change?
What did the
scientist
observe
(see)?
What was
kept the
same?
17