Other possible, but less often used scaling methods are discussed by ter Braak (1987c, 1990), including Canoco's scaling method 3 which is offered as an intermediate between the first two scaling options described above.
2 — Numerical example
The following example illustrates the calculations involved in correspondence analysis. In this numerical example, a species (abundance score, 3 classes) has been observed at 100 sites. The temperature (or any other environmental factor) at each site is coded from 1 (cold) to 3 (warm). The contingency table (Table 9.11) contains the number of sites at which each combination of the two descriptors was encountered. Subsection 4 will show that the same calculations may be conducted on a site x species data table, so that Table 9.11 can alternatively be seen as a numerical example for the latter, as indicated in italics in the Table. The data table is of small size (3 x 3), so as to allow readers to repeat the calculations.
Matrix Q contains the proportions py and the marginal distributions pi+ and p+y of the rows and columns, respectively. Identifiers of the rows and columns are given in parentheses, following Table 9.11:
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