Title: Controls and additive series
1Controls and additive series
2Group exercise Read your stream control
example, and decide on (1) What is wrong with
the design? (2) How you might fix it.
3Scenario 1
Before
After
4Scenario 2
B
C
A
pollutant
E
F
D
- pollutant
5What 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
6Scenario 3
Before
After
B
C
B
C
A
A
chemical in alkaline solution
Before
After
E
F
E
F
D
D
control
7Scenario 4
pollutant
control
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9Scenario 5
?
10Insect abundance m1 width m2 dioxin
m3 widthdioxin Y-intercept (and error)
11Summary 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?
12BACI design
Before After Control Impact
- Unmanipulated, contemporaneous control
- Initial conditions
- Eg. Scenario 3
Before
After
pollutant
Before
After
control
13BACI design
Before After Control Impact
- Unmanipulated, contemporaneous control
- Initial conditions
Before
After
control
pollutant
14Example of BACI design Ernest Leupins study on
forest fragments and birds
15Sicamous Creek Research Forest
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17How can we analyze BACI designs?
Randomized block?
What is n? What is k? How many independent
experimental units in total?
18How 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
19How can we analyze BACI designs?
Two separate ANOVAs / t-tests?
Different?
Different?
20How 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
21How 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
22How 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