Controls, blocks and randomization

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Controls, blocks and randomization
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Scenario 1
Before
After
3
Scenario 2
B
C
A
pollutant
E
F
D
- pollutant
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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
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Scenario 3
Before
After
B
C
B
C
A
A
chemical in alkaline solution
Before
After
E
F
E
F
D
D
control
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Scenario 4
pollutant
control
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(No Transcript)
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Scenario 5
?
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Insect abundance m1 width m2 dioxin
m3 widthdioxin Y-intercept (and error)
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Summary of control types

• Unmanipulated, contemporaneous control?
• Initial conditions?
• Controlled for side effect of manipulation?
• Controlled for non-target response?
• Controlled for covariates?

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BACI design

Before After Control Impact

• Unmanipulated, contemporaneous control
• Initial conditions
• Eg. Scenario 3

Before
After
pollutant
Before
After
control
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BACI design

Before After Control Impact

• Unmanipulated, contemporaneous control
• Initial conditions
• Eg. Scenario 3

Before
After
control
pollutant
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Example of BACI design Ernest Leupins study on
forest fragments and birds
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Sicamous Creek Research Forest
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(No Transcript)
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How can we analyze BACI designs?
Randomized block?
What is n? What is k? How many independent
experimental units in total?
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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
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How can we analyze BACI designs?
Two separate ANOVAs / t-tests?
Different?
Different?
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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
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How can we analyze BACI designs?

• Need to have match the number of datapoints with
  the number of experimental units
• Need to take advantage of built-in control for
  stream identity

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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