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Concepts of experimental design
Concepts of experimental design
independent variableindependent variable
dependent variabledependent variable
constantsconstants
control groupcontrol group
experimental group(s)
experimental group(s)
trialstrials
A variable is something that changes.
A variable is something that changes.
independent variableindependent variable
the variable that is changedthe variable that is changed on purposeon purpose by the by the
experimenterexperimenter
aka: chosen, cause, stimulus, tested, manipulated, etc.
aka: chosen, cause, stimulus, tested, manipulated, etc.
dependent variabledependent variable
the variable that responds
aka: observed, measured, effect(s), result(s),
measurement(s), etc.
aka: observed, measured, effect(s), result(s),
measurement(s), etc.
constantsconstants
all factors which are NOT allowed to change during the experiment stay the SAME
control groupcontrol group
the group used for comparison (the normal or no treatment
group)
experimental group(s)
experimental group(s)
the group(s) being tested with the independent
variable
Each test group has only one factor different from the other test groups: the independent
variable
Each test group has only one factor different from the other test groups: the independent
variable
TrialsTrials
the number of times the experiment is repeated
The more times you repeat the experiment, the more VALID your
results are.
The more times you repeat the experiment, the more VALID your
results are.
is used to design an experiment.
IVCDVIVCDVThe chart
iviv dvdvconstantconstantss
fertilizer
The variable (factor) that you will change is the independent variable.
The variable (factor) that you will change is the independent variable.
These are the fertilizer amounts chosen and changed by the experimenter.
These are the fertilizer amounts chosen and changed by the experimenter.
0 drops0 drops
2 drops2 drops
4 drops4 drops
6 drops6 drops
Plants with no fertilizer make up the control or control group.
Plants with no fertilizer make up the control or control group.
0 drops0 drops0 drops0 drops
iviv dvdvconstantconstantss
plant heightplant heightplant heightplant heightfertilizerfertilizer0 drops0 drops
2 drops2 drops
4 drops4 drops
6 drops6 drops
The variable (factor) resulting from the independent variable is the dependent variable.
The variable (factor) resulting from the independent variable is the dependent variable.
iviv dvdvconstants
constants
plant heightplant heightfertilizerfertilizer
amt. of amt. of waterwateramt. of amt. of waterwatertype of soiltype of soil
type of planttype of plant
type oftype of planterplantertype oftype of planterplantersize of plantersize of planter
amt. of soilamt. of soilamt. of soilamt. of soil
type of lighttype of lighttype of lighttype of light
locationlocation
0 drops0 drops
2 drops2 drops
4 drops4 drops
6 drops6 drops
These are the factors that must NOT change during experimentation. They
must remain constant.
These are the factors that must NOT change during experimentation. They
must remain constant.
no fe
rtili
zer
no fe
rtili
zer
2 dr
ops
fertili
zer
2 dr
ops
fertili
zer
4 dr
ops fe
rtili
zer
4 dr
ops fe
rtili
zer
6 dr
ops fe
rtili
zer
6 dr
ops fe
rtili
zer
no fe
rtili
zer
no fe
rtili
zer
2 dr
ops
fertili
zer
2 dr
ops
fertili
zer
4 dr
ops fe
rtili
zer
4 dr
ops fe
rtili
zer
6 dr
ops fe
rtili
zer
6 dr
ops fe
rtili
zerWhat is this called?What is this called?
CONTR
OL
What are these called?What are these called?
EXPER
IMEN
TAL
GROUP
EXPER
IMEN
TAL
GROUP
What are these called?What are these called?
CONSTANTS
CONSTANTS
00 22 44 66
What is this called?What is this called?
The plant growth that you observe here can be called . . .
The plant growth that you observe here can be called . . . the results (of adding fertilizer) the results (of adding fertilizer) the response (to adding fertilizer) the response (to adding fertilizer) the effects (of adding fertilizer) the effects (of adding fertilizer)
dependent
dependent
variable
variable
Form a
• Include the IV and DV• Must be testable!• Include the IV and DV• Must be testable!
list and describe
Specify size, amount, type, etc.
Specify size, amount, type, etc.
write down step-by-step instructions
• Be detailed- anyone should be able to repeat your experiment EXACTLY!
• Include safety precautions!
• Be detailed- anyone should be able to repeat your experiment EXACTLY!
• Include safety precautions!
analyze
• Organize/create tables, charts, graphs, diagrams, etc.
• Calculate values- averages, totals, % change, etc.
• Organize/create tables, charts, graphs, diagrams, etc.
• Calculate values- averages, totals, % change, etc.
draw
1. Restate the
Question
3. EXPLAIN results- why
and how? Was
anything unexpected?
2. Is Your Hypothesis SUPPORTED
or REJECTED?
4. Sources of Error?
Changes and improvements
?
5. What NEXT?