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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

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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?