Report - ICP Forests
Report - ICP Forests
Report - ICP Forests
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154 Annex<br />
Annex IV<br />
Testing statistical significance of the differences in mean plot defoliation between two<br />
years of assessment.<br />
Differences between mean plot defoliation were statistically examined for Common Sample<br />
Plots (CSPs) using the following test statistic:<br />
t =<br />
x<br />
2009<br />
s<br />
n<br />
2<br />
2009<br />
− x<br />
2008<br />
s<br />
+<br />
n<br />
2<br />
2008<br />
where x2009 − x2008<br />
is the difference in mean plot defoliation between the assessments in 2008<br />
and 2009,<br />
s -<br />
the standard deviation of these differences,<br />
n 2009 , n 20008 - number of sample trees on plots being tested.<br />
The standard deviation s is calculated as follows<br />
s =<br />
( n<br />
2009<br />
−1)<br />
s<br />
n<br />
2009<br />
+ ( n2008<br />
−1)<br />
s<br />
+ n − 2<br />
2<br />
2009<br />
2008<br />
2<br />
2008<br />
with standard deviations s , s 2009 2008<br />
derived from the defoliation scores for the years 2009 and<br />
2008 on the plots investigated.<br />
The minimal difference for qualifying a plot as having changed its mean defoliation was 5 and<br />
more. This applies to the map in Annex I-5. This additional criterion to the formal statistical test<br />
was chosen since 5 is the highest accuracy in the assessment of defoliation in the field.
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