Red–blue plots for detecting clusters in count data |
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| Authors: | JNPerry LWinder JMHolland RDAlston |
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| Institution: | Department of Entomology &Nematology, IACR–Rothamsted Experimental Station, Harpenden, Herts. AL5 2JQ, U.K.; Department of Land Use and Rural Management, Seale-Hayne Faculty, University of Plymouth, Newton Abbot, Devon TQ12 6NQ, U.K.; The Game Conservancy Trust, Fordingbridge, Hampshire, SP6 1EF, U.K.; Cancer Research Group, Royal Manchester Children's Hospital, Manchester, U.K. |
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| Abstract: | A new index and four new graphical displays, termed "red–blue" plots, are presented to study and measure clustering in spatially referenced count data. The index can detect clusters in the form of patches, comprising several nearby large counts, and in the form of gaps, comprising several nearby small counts. The new methods quantify the degree to which the count for each sample unit contributes towards the overall degree of clustering, either as part of a patch or as a gap; provide tests of nonrandomness to detect clustering; and facilitate a comprehensive definition of the size and dimension of a cluster. The methods are illustrated using aphid field data. |
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| Keywords: | Aggregation aphids biometry clusters counts heterogeneity patchiness population density SADIE spatial pattern |
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