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EEB375H1
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Laurel Duquette
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# EEB375 Stats Summary for Exam

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University of Toronto St. George

Ecology & Evolutionary Biology

EEB375H1

Laurel Duquette

Fall

Description

Estimating Population Dispersion
• s /mean > 1.0 = clumped distribution
• s /mean = 1.0 = random distribution
• s /mean < 1.0 = uniform distribution
Statistics
∑ (x−X) 2
• Variance (mean deviation): s =
n−1
2
• Standard deviation: STD =√s =
∑ (x−X) 2
√ n−1
STD
• Standard error: SE =
√N
• Confidence Interval: CI = 2*SE
• Upper CI = average + CI
• Lower CI = average – CI
Variance
• Population Dispersion =
Mean
One measure is simply the sum of the deviations of each obs from the mean. But
since this sum will always be zero, the average variance would always be zero
as well.
- The other method is to square each deviation and then sum the values. Squaring
the deviations eliminates the zeros which means that the sum will be a positive,
non-zero number that accurately reflects the degree of deviation (larger deviation
means a larger value of variance and vice versa). The drawback is that the
variance is a unit-less measure so it hard to equate it back to the original
measurements.
- SD is the square root of Variance which means that SD expresses deviation in
the original units of measure. R

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