On-line statistics

Soerensen's Quotient

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This is a simple method for evaluating the similarity between two quadrat samples. It has the advantage of not requiring an estimate of the number of individuals of each species. This means however that it would not differentiate between the samples used as examples for Peterson's Homogeneity Index where although all four species are present in each sample their proportions vary enormously. Søerensen's Quotient is particularly useful in situations where it is difficult to quantify the numbers of individuals of each species present in an area (e.g. large quadrats with many small plants, coral reef surveys or transect samples).

Søerensons Quotient (the SQ value) for sites X and Y is given as 2J/(A+B) where

A = number of species in site X
B = number of species in site Y
J = number of species common to both

The value will be close to 1.0 for sites that have most of their species in common and for very dissimilar sites the value would be close to 0.0.

Example

To calculate the SQ value for samples A and B:

A = 3, B = 2 and J = 1, therefore SQ(A,B) = 2/5 = 0.4

Now check that you understand by completing the following:

Question #1:
If, upon closer examination, one or two elephants were noticed in Sample A what would be the new SQ(A,B) value? :

Question #2:
If all four species were present in A what would be the SQ(A,C) value :
Correct Answers

Several samples can be compared by cluster analysis using Nearest neighbour sorting (a simple method for the production of cladograms).

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Descriptive Stats

Diversity Indices

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Regression