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en:similarity [2019/02/23 07:44]
David Zelený [Similarity, dissimilarity and distance]
en:similarity [2019/02/26 22:08]
David Zelený [Double-zero problem]
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 <​imgcaption double-zero-table |For details see the text.>{{ :​obrazky:​double-zero-table.jpg?​direct&​400|}}</​imgcaption>​ <​imgcaption double-zero-table |For details see the text.>{{ :​obrazky:​double-zero-table.jpg?​direct&​400|}}</​imgcaption>​
  
-<imgref double-zero-table>​ shows an ecological example of double zero problem. Samples 1 to 3 are sorted according to the wetness of their habitat – sample 1 is the wettest and sample 3 is the driest. In samples 1 and 3, no mesic species occur, since sample 1 is too wet and sample 3 too dry - these is the double zero. The fact that the mesic species is missing does not say anything about ecological similarity or difference between both samples; simply there is no information,​ and it is better to ignore it. In the case of symmetrical indices of similarity, the absence of mesic species in sample 1 and sample 3 (0-0, double zero) will increase similarity of sample 1 and 2; in asymmetrical indices, double zeros will be ignored and only presences (1-1, 1-0, 0-1) will be considered.+<imgref double-zero-table>​ shows an ecological example of double zero problem. Samples 1 to 3 are sorted according to the wetness of their habitat – sample 1 is the wettest and sample 3 is the driest. In samples 1 and 3, no mesic species occur, since sample 1 is too wet and sample 3 too dry - these is the double zero. The fact that the mesic species is missing does not say anything about ecological similarity or difference between both samples; simply there is no information,​ and it is better to ignore it. In the case of symmetrical indices of similarity, the absence of mesic species in sample 1 and sample 3 (0-0, double zero) will increase similarity of sample 1 and 3; in asymmetrical indices, double zeros will be ignored and only presences (1-1, 1-0, 0-1) will be considered.
  
  
en/similarity.txt · Last modified: 2019/02/26 22:08 by David Zelený