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Scientific Method - Scientific Method - Controls and VariablesControls and Variables

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Scientific Experiments Scientific Experiments Follow RulesFollow Rules..

• An experimenter An experimenter changes ONE changes ONE factor and factor and observes or observes or measures what measures what happens.happens.

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Manipulated and Manipulated and Responding Variables?Responding Variables?• The factor that is changed is The factor that is changed is

known as the known as the manipulated manipulated variablevariable. .

• The factor that is measured or The factor that is measured or observed is called the observed is called the responding variableresponding variable. .

• What are the manipulated and What are the manipulated and responding variables in your E. responding variables in your E. coli experiment?coli experiment?

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Control Variables?Control Variables?

• The experimenter makes a The experimenter makes a special effort to keep special effort to keep other other factors constantfactors constant so that they will so that they will not effect the outcome.not effect the outcome.

• Those factors are called Those factors are called control control variables.variables.

• What are some of the control What are some of the control variables in your E. coli variables in your E. coli experiment?experiment?

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Experimental Control?Experimental Control?• The experimenter needs to be able to The experimenter needs to be able to

see if the thing they manipulated had see if the thing they manipulated had an effect on the outcome of the an effect on the outcome of the experiment.experiment.

• They do this by comparing to an They do this by comparing to an identical experiment where the identical experiment where the manipulated variable was either manipulated variable was either missing or remained unchanged.missing or remained unchanged.

• This is the This is the Experimental ControlExperimental Control..• What is the experimental control in What is the experimental control in

your E. coli experiment?your E. coli experiment?

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What is the purpose of What is the purpose of an Experimantal an Experimantal

Control?Control?•Controls are NOT being

tested.•Controls are used for COMPARISON

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An example of An example of Controls & Controls & VariablesVariables

• For example, suppose you want to For example, suppose you want to figure out the fastest route to walk figure out the fastest route to walk home from school. You will try several home from school. You will try several different routes and time how long it different routes and time how long it takes you to get home by each one. takes you to get home by each one.

• Since you are only interested in finding Since you are only interested in finding a route that is fastest for you, you will a route that is fastest for you, you will do the walking yourself.do the walking yourself.

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What are the Variables What are the Variables in Your Experiment?in Your Experiment?

• Varying the route is the Varying the route is the manipulated variablemanipulated variable

• The time it takes is the The time it takes is the responding responding variablevariable

• Keeping the same walker Keeping the same walker throughout makes the walker a throughout makes the walker a control variable. control variable. Name some others.Name some others.

• You pick one route to be the You pick one route to be the experimental controlexperimental control and compare and compare the other routes to it. the other routes to it.

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• One more thing… it is best to make several trials with each manipulated variable.

• This gives you an increased confidence in your data.

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