The Basics of Experimental Design Gregory M. Williams, Ph.D. Hudson Regional Health Commission
Overview Why? Scientific Method Analysis Example Questions
Why do Research? To answer questions To publish For money Personal satisfaction
The Scientific Method A series of steps for conducting scientific research
The Scientific Method 1.Observe 2.Question 3.Guess 4.Test 5.Conclusions 6.Retest
Example Discovery and testing of a new mosquito larvicide.
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.
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?
Literature Review What have others done? Check relevant journals –JAMCA, JME, VBZD, JVE Learn –larvicidal bioassay Don’t want to repeat Search for keywords-ashtray, tobacco, nicotine, mosquito…
Form a Hypothesis What is answer? Prediction “If…then” logic If ashtray water contains a larvicidal compound…then it should kill larvae placed in it.
Hypothesis 1.Explanation 2.Reflect experience 3.Multiple hypotheses Environmental conditions Oviposition deterent 4.Must be testable
Design the Experiment Identify the variables –Independent What you are testing –Ashtray water –Dependent What you measure –Larval mortality
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.
Experiment Test your hypothesis Replication –More is better!
Analyze the Results Statistics Calculations to determine how good data are Are results real or chance? Compare deviations to results Treatment vs. control
Draw Conclusions No difference between trt. & con. or con. > trt. –Ashtray water is not larvicidal Mortality of trt. > con. –Ashtray water is larvicidal
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?
Closing Thoughts Each answer leads to more questions!
Questions?