QUANTIFICATION OF PARASITE AGGREGATION - A SIMULATION STUDY

A simulation study is used to examine the statistical behaviour of est imators of parameters of parasite infection in relation to variation i n sample size, the degree of parasite aggregation, and mean parasite b urden. The most important patterns to emerge are the associations betw een estimates of parameters and sample size (= number of host individu als). As sample size decreases values of sample mean parasite burden, its associated variance, and the level of parasite aggregation are all systematically underestimated. The geometric mean of parasite burden and the prevalence of infection appear to be independent of associatio ns with other parasite parameters. Estimates of parameter values may a lso depend on the underlying frequency distribution, but appear insens itive to variation in the population mean parasite burden. Results are discussed in relation to the interpretation of data derived from fiel d-based studies. In particular, establishing the form of the relations hip between host age and mean parasite burden and/or the degree of par asite aggregation. It is typical for sample size to decline as a funct ion of host age within cross-sectional field data. This may give rise to artefactual patterns in the shape of age-aggregation curves in whic h sample sizes are unequal among host age classes.