APPCOR10264

• Permit No: C1981015
• IBM Index Class Name: Application Correspondence
• Doc Date: 8/6/1983
• From: DORCHESTER COAL CO
• To: MLR
• Media Type: D
• Archive: No

•
2.0 Methods. .
2.8 Sample Adequacy
•
Sample adequacies for cover, production, and density were calculated
separately for the affected. and reference areas in each vegetation type.
The sample adequacy formula is as follows:
t=s=
n _
min d'z'
where nmin = minimum sample size
t = t value for 2-tailed test with infinite. degrees of freedom
(t = 1.282 for 80% confidence; and 1.646 for 90% confidence)
s = sample standard deviation (n-1)
d = desired detectable change in the mean (10%)
x = sample mean
All parameters were tested at the 80 percent confidence level
for shrubland vegetation types and at the 90 percent confidence level for
herbaceous vegetation types.
The statistical comparability between reference and affected area
vegetation cover and herbaceous production was evaluated using methods
recommended by CMLR. For each pair of reference and affected areas, a .
t value is calculated as follows for cover and then for production:
t = SxA-TXR
s, s, xA - xR
where sx - xR nP + nP
A A B
dAsA + dRsR
and sP = ~-
A R
xA = affected area mean
xR = reference area mean
s' - =the variance of the difference between the means
xA-xR
sP = pooled variance
nA = affected area sample size
--~'F'~i
~,~.