Document Detail


The contribution of simple random sampling to observed variations in faecal egg counts.
MedLine Citation:
PMID:  22521975     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
It has been over 100 years since the classical paper published by Gosset in 1907, under the pseudonym "Student", demonstrated that yeast cells suspended in a fluid and measured by a haemocytometer conformed to a Poisson process. Similarly parasite eggs in a faecal suspension also conform to a Poisson process. Despite this there are common misconceptions how to analyse or interpret observations from the McMaster or similar quantitative parasitic diagnostic techniques, widely used for evaluating parasite eggs in faeces. The McMaster technique can easily be shown from a theoretical perspective to give variable results that inevitably arise from the random distribution of parasite eggs in a well mixed faecal sample. The Poisson processes that lead to this variability are described and illustrative examples of the potentially large confidence intervals that can arise from observed faecal eggs counts that are calculated from the observations on a McMaster slide. Attempts to modify the McMaster technique, or indeed other quantitative techniques, to ensure uniform egg counts are doomed to failure and belie ignorance of Poisson processes. A simple method to immediately identify excess variation/poor sampling from replicate counts is provided.
Authors:
Paul R Torgerson; Michaela Paul; Fraser I Lewis
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-3-30
Journal Detail:
Title:  Veterinary parasitology     Volume:  -     ISSN:  1873-2550     ISO Abbreviation:  -     Publication Date:  2012 Mar 
Date Detail:
Created Date:  2012-4-23     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  7602745     Medline TA:  Vet Parasitol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Copyright © 2012 Elsevier B.V. All rights reserved.
Affiliation:
Section of Epidemiology, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 270, Zurich 8057, Switzerland.
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