# Experimental Design How to design an experiment..

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Experimental Design How to design an experiment.

Constants & Variables Constant: Constant: Variable: Variable:

Constants & Variables Constant: all factors that are kept the same in an experiment. Constant: all factors that are kept the same in an experiment. Variable: all factors that change in an experiment Variable: all factors that change in an experiment

Variables Independent Variable Independent Variable Dependent Variable Dependent Variable

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

Variables Independent Variable Independent Variable (or Manipulated Variable) The variable that is purposively changed by researcher Beginning researchers should limit to 1 May use different levels Dependent Variable Dependent Variable (or Responding Variable) The variable that responds in an experiment (It depends on the independent variable)

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

Hypothesis A proposed answer to a research question A proposed answer to a research question A tentative explanation that is testable A tentative explanation that is testable A testable prediction that stems from a theory or explanation A testable prediction that stems from a theory or explanation An educated guess??? An educated guess???

Hypothesis A testable prediction about how changes in the independent variable will affect the dependent variable. A testable prediction about how changes in the independent variable will affect the dependent variable. Often written in an if-then format: Often written in an if-then format: “If the _______ is _______, then the _______ will _______.”

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

Hypothesis 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 Group The standard for comparing experimental effects. The standard for comparing experimental effects. No treatment control No treatment control Experimenter selected control Experimenter selected control

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

4-Question Strategy Q1 What materials are readily available for conducting experiments on______? Q2 How do _____ act? Q3 How can I change the set of _____ materials to affect the action? Q4 How can I measure or describe the response of _____ to the change?

4-Question Strategy Independent Variable: Independent Variable: Dependent Variable: Dependent Variable: Hypothesis: Hypothesis: Constants: Constants:

4-Question Strategy Independent Variable: Choose from Q3 Independent Variable: Choose from Q3 Dependent Variable: Choose from Q4 Dependent Variable: Choose from Q4 Hypothesis: Hypothesis: Constants: Constants:

4-Question Strategy Independent Variable: Choose from Q3 Dependent Variable: Choose from Q4 Hypothesis: Relate Q3 to Q4: Hypothesis: Relate Q3 to Q4: If I change ( I.V. from Q3 ), then the ( D.V. from Q4 ) will ( describe predicted change ). If I change ( I.V. from Q3 ), then the ( D.V. from Q4 ) will ( describe predicted change ). Constants: All other responses to Q3 Constants: All other responses to Q3

Experimental 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 Diagram Independent Variable: Age of Compost no compost (control) 3-month-old compost 6-month-old compost 25 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 Diagram Independent Variable: (Selected from Q #3) Title: The Impact of _________ on __________ Relate Q3 to Q4) Hypothesis: (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)