The Natural Pattern of Dilution Counts of Helminth Eggs

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Abstract Summary

Egg count data are discussed here from a theoretical viewpoint as a step toward a practical standardized analytic procedure. Such data from a natural population group form a J shaped curve as ordinarily plotted, since most persons pass small numbers of eggs while relatively few pass very many. When the data are plotted on a logarithmic scale, an approximate normal curve results only when the average is unusually high and the number of cases lost below the lower counting limit is therefore unappreciable. Data presented here demonstrate that most averages of egg counts have been unequally biased by the variable size of this missing portion of the curve. Statistical analysis of the data on a logarithmic scale requires no special mathematical knowledge and offers certain definite advantages. The resulting constants, although expressed in compact form, provide material for such additional analyses and comparisons as the reader may wish to make. In addition, visualization of the data is easier on a logarithmic scale.