Experimental Design

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  • 1. Hypothesis Controlled Experiment and Variable Independent and Dependent Variable Sample Size and Validity Scientific Method and Experimental Design
  • 2. Steps of the Scientific Method
    • Make observations.
    • Ask a question.
    • Form a hypothesis.
    • Test the hypothesis.
    • Analyze the results.
    • Draw conclusions.
    • Communicate the results.
  • 3. Hypothesis An explanation of a natural event or observation that can be tested by additional observations or experimentation
  • 4. Example of Hypothesis Observation: The population of tiger salamanders declined 65% between 1984 and 1988 Hypothesis: Acids that were formed in the upper atmosphere by pollutants were falling onto mountains in the winter snows
  • 5. Controlled Experiment and Variable Tests one variable at a time (experimental variable) Controlled experiments include 2 groups: Experimental Group Exposed to experimental variable Control Group Not exposed to experimental variable
  • 6. Independent and Dependent Variables Independent variable : The factor that is deliberately manipulated in an experiment (also called experimental variable) Dependent variable : The variable that is changed or determined by manipulation of the independent variable. It is what is measure in the experiment
  • 7.
    • Sample Size
    • Sample Size (N)
    • The number of subjects involved in experimentation
    • Increasing N
      • Decreases impact of chance events and error
      • Increase reliability of results
  • 8. Why does a good experiment need to have two parts, including a control?
    • It isolates and tests the effects of one variable at a time
    • Provides certainty that the change is due to the effect of the variable being tested
  • 9. Validity The extent to which experimental results can be generalized to other settings or situations To increase validity, increase N