The Basics of Experimental Design

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The Basics of Experimental Design

• Gregory M. Williams, Ph.D.
• Hudson Regional Health Commission

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Overview

• Why?
• Scientific Method
• Analysis
• Example
• Questions

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Why do Research?

• To answer questions
• To publish
• For money
• Personal satisfaction

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The Scientific Method

• A series of steps for conducting scientific
  research

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The Scientific Method

1. Observe
2. Question
3. Guess
4. Test
5. Conclusions
6. Retest

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Example

• Discovery and testing of a new mosquito larvicide.

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Observations

• You are always observing
• Look at the data
• Traps
• Larval surveillance
• Infection rates
• Weather
• You notice that there are never any mosquito
  larvae in outdoor ashtray.

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Question

• As you Observe you are faced with questions
• Why is my data the way it is?
• Pick a question to test
• Question should be yes/no
• Does water in ashtray act as a larvicide?

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Literature Review

• What have others done?
• Check relevant journals
• JAMCA, JME, VBZD, JVE
• Learn
• larvicidal bioassay
• Dont want to repeat
• Search for keywords-ashtray, tobacco, nicotine,
  mosquito

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Form a Hypothesis

• What is answer?
• Prediction
• Ifthen logic
• If ashtray water contains a larvicidal
  compoundthen it should kill larvae placed in it.

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Hypothesis

• Explanation
• Reflect experience
• Multiple hypotheses
• Environmental conditions
• Oviposition deterent
• Must be testable

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Design the Experiment

• Identify the variables
• Independent
• What you are testing
• Ashtray water
• Dependent
• What you measure
• Larval mortality

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Design the Experiment

• Experimental groups
• Treatment group
• Receives the treatment
• Larvae in ashtray water
• Control group
• No treatment
• Otherwise identical
• Larvae in plain water
• Normalize conditions
• Temp, light, containers, etc.

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Experiment

• Test your hypothesis
• Replication
• More is better!

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Analyze the Results

• Statistics
• Calculations to determine how good data are
• Are results real or chance?
• Compare deviations to results
• Treatment vs. control

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Draw Conclusions

• No difference between trt. con. or con. gt trt.
• Ashtray water is not larvicidal
• Mortality of trt. gt con.
• Ashtray water is larvicidal

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Follow-up

• What compound in the ashtray water is acting as
  larvicide?
• Nicotine, sand, other
• Is the effect dose dependent?
• Does this hold true for other ashtrays?

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Closing Thoughts

• Each answer leads to more questions!

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Questions?