Experimental DesignExperimental Design

How to design an experiment.How to design an experiment.

Constants & VariablesConstants & Variables

ConstantConstant::

VariableVariable::

Constants & VariablesConstants & Variables

ConstantConstant:: all factors that are kept the all factors that are kept the same in an experiment.same in an experiment.

VariableVariable:: all factors that change in an all factors that change in an experimentexperiment

VariablesVariables

Independent VariableIndependent Variable

Dependent VariableDependent Variable

VariablesVariables

Independent VariableIndependent Variable (or Manipulated Variable) (or Manipulated Variable) The variable that is purposively changed by researcherThe variable that is purposively changed by researcher Beginning researchers should limit to 1Beginning researchers should limit to 1 May use different levelsMay use different levels

Dependent VariableDependent Variable

VariablesVariables

Independent VariableIndependent Variable (or Manipulated Variable) The variable that is purposively changed by researcher Beginning researchers should limit to 1 May use different levels

Dependent VariableDependent Variable (or Responding Variable) The variable that responds in an experiment (It depends on the independent variable)

HypothesisHypothesis

An educated guess???An educated guess??? An educated guess???An educated guess???

HypothesisHypothesis

An educated guess???An educated guess???

A proposed answer to a research questionA proposed answer to a research question

A tentative explanation that is testableA tentative explanation that is testable

A testable prediction that stems from a theory or A testable prediction that stems from a theory or explanationexplanation

An educated guess???An educated guess???

HypothesisHypothesis

A testable prediction about how changes in the A testable prediction about how changes in the independent variable will affect the dependent independent variable will affect the dependent variable.variable.

Often written in an if-then format:Often written in an if-then format:

““If the _______ is _______ , then the _______ will _______ .”If the _______ is _______ , then the _______ will _______ .”

HypothesisHypothesis

A testable prediction about how changes in the independent variable will affect the dependent variable.

Often written in an if-then format:

““If the _______ is _______ , then the _______ will _______ .”If the _______ is _______ , then the _______ will _______ .”

(Ind.Variable) (Describe Change) (Ind.Variable) (Describe Change) (Dep. Variable) (Describe (Dep. Variable) (Describe effect)effect)

HypothesisHypothesis

A testable prediction about how changes in the independent variable will affect the dependent variable.

Often written in an if-then format:

“If the _______ is _______ , then the _______ will _______ .” (Ind.Variable) (Describe Change) (Dep. Variable) (Describe effect)

Supported, not proven!Supported, not proven!

Control GroupControl Group

The standard for comparing experimental The standard for comparing experimental effects.effects. No treatment controlNo treatment control Experimenter selected controlExperimenter selected control

Repeated TrialsRepeated Trials

The number of experimental repetitions, objects, The number of experimental repetitions, objects, or organisms tested at each level of the or organisms tested at each level of the independent variable.independent variable.

4-Question Strategy4-Question Strategy

Q1Q1 What materials are readily available for What materials are readily available for conducting experiments on______?conducting experiments on______?

Q2 Q2 How do _____ act?How do _____ act?

Q3 Q3 How can I change the set of _____ materials to How can I change the set of _____ materials to affect the action?affect the action?

Q4 Q4 How can I measure or describe the response of How can I measure or describe the response of _____ to the change? _____ to the change?

4-Question Strategy4-Question Strategy

Independent VariableIndependent Variable: :

Dependent VariableDependent Variable::

HypothesisHypothesis::

ConstantsConstants::

4-Question Strategy4-Question Strategy

Independent VariableIndependent Variable: Choose from Q3: Choose from Q3

Dependent VariableDependent Variable: Choose from Q4: Choose from Q4

HypothesisHypothesis: :

ConstantsConstants::

4-Question Strategy4-Question Strategy

Independent Variable: Choose from Q3

Dependent Variable: Choose from Q4

HypothesisHypothesis: Relate Q3 to Q4:: Relate Q3 to Q4:

If I change If I change ((I.V. from Q3I.V. from Q3), then the ), then the ((D.V. from Q4D.V. from Q4)) will will ((describe predicted changedescribe predicted change).).

ConstantsConstants: All other responses to Q3: All other responses to Q3

Experimental Design DiagramExperimental Design Diagram

Independent Variable:

Title:

Hypothesis:

Dependent Variable:

Constants:

Levels of Independent Variable (including the control)

Repeated Trials (# of times each I.V. level will be tested)

Experimental Design DiagramExperimental Design Diagram

Independent Variable: Age of Compost

no compostno compost

(control)(control)

3-month-old compost3-month-old compost 6-month-old compost6-month-old compost

25 plants25 plants 25 plants25 plants 25 plants25 plants

Title: The Effect of Different Aged Compost on Bean Plant Growth

Hypothesis: If older compost is applied, then plant growth will be increased.

Dependent Variable: Mass of plants (g)—dry

Constants: light, water, soil, temp., amount & type of compost

Experimental Design DiagramExperimental Design Diagram

Independent Variable: (Selected from Q #3)

Title: The Impact of _________ on __________

Hypothesis: (Relate Q3 to Q4)Relate Q3 to Q4)

Dependent Variable: (Selected from Q #4)

Constants: (All factors from Q #3 that you didn’t choose)

Levels of Independent Variable (including the control)

Repeated Trials (# of times each I.V. level will be tested)