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4.3 What are Good and Poor Ways to Experiment?

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Learning Objectives:

• Identify elements of experiment• Experiments• 3 components of good experiments• Blinding the study• Statistical Significance• Generalizing results of the study reactorfire.files.wordpress.com

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Elements of an Experiment

• Experimental units: Subjects• Treatment: Conditions imposed on subjects• Explanatory variable: Defines groups and treatments• Response variable: Outcome

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Experiments

• Impose treatments on subjects to observe responses• Goal: compare effects of treatments on response• Randomized experiments – subjects randomly assigned to treatments

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Placebo effect

Placebo – fake treatment; sugar pillPlacebo effect –improving not from real treatment but from belief that he or she should improve

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3 Components of a Good Experiment

• Control or Comparison Group• Randomization• Replication

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Principle 1: Control or Comparison Group

• Helps analyze effectiveness of primary treatment • Placebo removes lurking variables• Control group gets placebo• Clinical trials may compare new treatment with existing

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• Experiments should compare treatments rather than effect of single treatment• Example: 400 volunteers asked to quit smoking with some taking and some not taking antidepressant

Control or Comparison Group

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Principle 2: Randomization

• Eliminates bias from researcher assigning subjects• Balances groups on known and lurking variables

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Principle 3: Replication

• Reduces difference due to ordinary variation or chance• Increases chance that results show true difference• Every subject assigned to a treatment is a replication

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Blinding the Experiment

• Blind – subjects unaware of which treatment used• Double-Blind Experiment - Neither subjects nor investigators know which treatment• Controls bias from respondent and experimenter

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Statistically Significant Difference – Observed difference is larger than expected from chance

Statistical Significance

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Generalizing Results

• Goal of Experimentation – Analyze association between treatment and response for entire population• Generalize only to population represented by study

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