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Controls and additive series

Controls and additive series. Rule #1 Make sure your control, is actually a control e.g. non-lethal presence of predators in bromeliads…. Caged Predator. Free Predator. No Predator. Caged Predator. Free Predator. No Predator. Additive controls… Group exercise:

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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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