designing an
A variable is something that
changes.
6 components of an experiment
independent variable
dependent variable
constants
control group
experimental group
repeated trials
independent variable
the variable that is changed
on purpose by the experimenter
aka cause, stimulus, reason,
manipulated variable, etc.
dependent variable
the variable that changes in
response to the independent
variable
aka effect(s), result(s), responding
variable, etc.
constants
all the factors which are NOT
allowed to change during the
experiment
control group
the group (standard) to which
everything is compared
experimental group
the group(s) being tested using
the independent variable
Each test group has only one factor
different from the other test groups:
the independent variable.
repeated trials
the number of times the experiment
is repeated
An experiment should be carried out
many times to produce accurate/
repeatable results
Before carrying out an experiment,
you MUST identify your independent
variable, constants and dependent
variable.
What is this called? What are these called?
What are these called?
What is this called?
The plant growth that you
observe here can be called . . .
 the results (of adding fertilizer)
 the response (to adding fertilizer)
 the effects (of adding fertilizer)
0
2
4
6
forming a
A good hypothesis:
- Is a statement (NOT a question)
- Is written in clear and simple language
- Relates the independent and dependent
variables
- Is testable
- Can be written in several ways
(including if, then statement)
Write a hypothesis for the plant
experiment in the box in your notes.
Good or Bad Hypothesis?
- Warm water will dissolve more
salt than cold water.
What is another way this hypothesis
can be written?
Good or Bad Hypothesis?
- Will fertilizer make my lawn grow
more?
How can you make this a good
hypothesis?
recording and displaying
iv
fertilizer
constants
dv
plant growth
0 drops
2 drops
4 drops
6 drops
Results from your
experimentation should be
recorded in a carefully
constructed data table.
iv
dv
constants
fertilizer
plant growth
0 drops
1 cm
2 drops
1.5 cm
4 drops
1.5 cm
6 drops
3 cm
A data table has at least 2
columns of information.
Independent variable data is always
(a) recorded in the left column
(b) recorded BEFORE experimentation
fertilizer
0 drops
2 drops
4 drops
6 drops
IV
fertilizer
fertilizer (drops)
0 drops
0
2 drops
2
4 drops
4
6 drops
6
Dependent variable data is always
(a) recorded in the right column
(b) recorded DURING experimentation
plant growth
fertilizer (drops)
1 cm
0
1.5 cm
2
1.5 cm
4
3 cm
6
DV
plant growth
fertilizer (drops) plant growth (cm)
1 cm
0
1
1.5 cm
2
1.5
1.5 cm
4
1.5
3 cm
6
3
Choose an appropriate title for the
data table.
Effect of Fertilizer on Plants Growth
fertilizer (drops) plant growth (cm)
0
1
2
1.5
4
1.5
6
3
Data from a correctly constructed
data table can be displayed in a
graph.
Effect of Fertilizer on Plants
fertilizer (drops) plant growth (cm)
0
1
2
1.5
4
1.5
6
3
IV data is plotted on the X axis.
DV data is plotted on the Y axis.
Effect of Fertilizer on Plants
plant growth (cm)
0
1
2
1.5
4
1.5
6
3
3.0
2.5
plant growth (cm)
fertilizer (drops)
2.0
1.5
1.0
.5
0
2
4
fertilizer (drops)
6
The title of the data table is also the
title of the graph.
Effect of Fertilizer on Plants
Effect of Fertilizer on Plants
plant growth (cm)
0
1
2
1.5
4
1.5
6
3
3.0
2.5
plant growth (cm)
fertilizer (drops)
2.0
1.5
1.0
.5
0
2
4
fertilizer (drops)
6