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Experimental Design – how to design an experiment to test a hypothesis

Experimental Design – how to design an experiment to test a hypothesis. Biology I Honors. After Observing…. A problem or something that raises a question and… After doing background research and developing a hypothesis… You need to test the hypothesis

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Experimental Design – how to design an experiment to test a hypothesis

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  1. Experimental Design – how to design an experiment to test a hypothesis Biology I Honors

  2. After Observing… • A problem or something that raises a question and… • After doing background research and developing a hypothesis… • You need to test the hypothesis • There are several ways to do this. One of these is setting up a controlled experiment.

  3. Controlled Experiment • Designed to test a hypothesis • The elements of a controlled experiment are…

  4. Elements of a Controlled Experiment • Two or more set-ups of the experiment • Experimental treatment(s) • A set-up of the experiment that will have something “done to it” • May be more than 1 treatment (or set up) • Control treatment • A set-up of the experiment that will have NOTHING done to it • Standard of Comparison • Allows you to compare a “normal” situation to the experimental situation so that you can determine if your experimental variable is having an effect on results.

  5. Elements of a Controlled Experiment • Variables • Anything that is altered or that “varies” among set-ups (treatments) of an experiment. • Ideally, however, NOTHING varies between set-ups EXCEPT what you want to test. • Why? • If more than one variable is different between the set-ups, then there will be no way to know which variable is affecting results.

  6. Elements of a Controlled Experiment • Constants • All those POTENTIAL variables that are maintained the SAME for all set-ups of the experiment.

  7. Elements of a Controlled Experiment • Two Particularly Important Variables: • Independent (manipulated) Variable • Dependent (responding) Variable

  8. Elements of a Controlled Experiment • Independent Variable • The variable that is PURPOSEFULLY altered in an experimental treatment • There may be several “levels” to the IV • For example: Amount of Water given to plants • Amount of Water • 10 ml / day (“level 1” of the IV) • 25 ml / day (“level 2” of the IV) • 50 ml / day (“level 3” of the IV)

  9. Elements of a Controlled Experiment • Dependent Variable • The thing that is MEASURED as your experimental results • Example: Plant growth (in response to amount of water given)

  10. Trials • Multiple trials • Repetitions of an experiment • Do as many as possible • Typically 3 in class; or as many as there are lab groups (each lab group does a trial) • TRIALS DO NOTELIMINATE ERROR! • Mulitple trials DO REDUCE EFFECTS OF ERROR ON RESULTS!

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