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Controls and additive series

Explore different control types in experimental designs and how to analyze BACI designs for accurate results. Learn to identify and address control issues for robust scientific findings.

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Controls and additive series

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  1. Controls and additive series

  2. Rule #1 Make sure your control, is actually a control e.g. non-lethal presence of predators in bromeliads….

  3. Caged Predator Free Predator No Predator

  4. Caged Predator Free Predator No Predator

  5. Additive controls… Group exercise: Read your stream control example, and decide on: (1) What is wrong with the design? (2) How you might fix it.

  6. C C A A B B Scenario 1 Before After

  7. Scenario 2 B C A + pollutant E F D - pollutant

  8. What is the probability that the 3 “worst” streams are randomly assigned to the pollutant treatment? 3/6 * 2/5 * 1/4 = 2/40 or 5%

  9. Scenario 3 Before After B C B C A A + chemical in alkaline solution Before After E F E F D D control

  10. Before After B C B C A A Before After E F E F D D Scenario 4 + pollutant control

  11. Scenario 5 ?

  12. Insect abundance = m1 * width + m2 * dioxin + m3 * width*dioxin + Y-intercept (and error)

  13. Summary of control types • Which scenarios lacked: • Control for initial conditions? • Unmanipulated, contemporaneous control? • Control for side effect of manipulation? • Control for covariates? • Control for non-target response?

  14. BACI design Before After Control Impact • Unmanipulated, contemporaneous control • Initial conditions • Eg. Scenario 3 Before After + pollutant Before After control

  15. BACI design Before After Control Impact • Unmanipulated, contemporaneous control • Initial conditions Before After control + pollutant

  16. Example of BACI design: Ernest Leupin’s study on forest fragments and birds

  17. Sicamous Creek Research Forest

  18. A treatment x date ANOVA? Before After A B C A B C + pollutant Before After control D E F D E F How can we analyze BACI designs? Randomized block? What is n? What is k? How many independent experimental units in total?

  19. Before After + pollutant Before After control How can we analyze BACI designs? Randomized block? A treatment x date ANOVA? What is n? What is k? How many independent experimental units in total? A B C G H I D E F J K L

  20. Before After + pollutant Before After control How can we analyze BACI designs? Two separate ANOVAs / t-tests? Different? Different?

  21. How can we analyze BACI designs? Two separate ANOVAs / t-tests? Impact sites Y variable before after before after before after before after A B C

  22. How can we analyze BACI designs? • Need to match the number of datapoints with the number of experimental units • Need to take advantage of built-in control for stream identity

  23. How can we analyze BACI designs? One solution: Use difference between before and after as the data! Before After Difference A B C A B C A B C + pollutant Before After Difference control D E F D E F D E F

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