Analysis of aggregation, a worked example: numbers of ticks on red grouse chicks

D. A. Elston, R. Moss, T. Boulinier, C. Arrowsmith, Xavier Lambin

Research output: Contribution to journalArticlepeer-review

313 Citations (Scopus)


The statistical aggregation of parasites among hosts is often described empirically by the negative binomial (Poisson-gamma) distribution. Alternatively, the Poisson-lognormal model can be used. This has the advantage that it can be fitted as a generalized linear mixed model, thereby quantifying the sources of aggregation in terms of both fixed and random effects. We give a worked example, assigning aggregation in the distribution of sheep ticks Ixodes ricinus on red grouse Lagopus lagopus scoticus chicks to temporal (year), spatial (altitude and location), brood and individual effects. Apparent aggregation among random individuals in random broods fell 8-fold when spatial and temporal effects had been accounted for.

Original languageEnglish
Pages (from-to)563-569
Number of pages6
Publication statusPublished - 2001


  • analysing aggregation
  • generalized linear mixed model
  • Ixodes ricinus
  • Lagopus lagopus scoticus
  • Poisson-lognormal distribution
  • variance components


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