Folia Parasitologica, vol. 64 (2017)

Folia Parasitologica 64:025 (2017) | DOI: 10.14411/fp.2017.025

Do small samples underestimate mean abundance? It depends on what type of bias we consider

Jenő Reiczigel1, Lajos Rózsa2,3
1 Department of Biomathematics and Informatics, University of Veterinary Medicine, Budapest, Hungary;
2 Hungarian Academy of Sciences, MTA-ELTE-MTM Ecology Research Group, Budapest, Hungary;
3 Hungarian Academy of Sciences, MTA Centre for Ecological Research, Evolutionary Systems Research Group, Tihany, Hungary

Former authors claimed that, due to parasites' aggregated distribution, small samples underestimate the true population mean abundance. Here we show that this claim is false or true, depending on what is meant by 'underestimate' or, mathematically speaking, how we define 'bias'. The 'how often' and 'on average' views lead to different conclusions because sample mean abundance itself exhibits an aggregated distribution: most often it falls slightly below the true population mean, while sometimes greatly exceeds it. Since the several small negative deviations are compensated by a few greater positive ones, the average of sample means approximates the true population mean.

Keywords: sampling bias, sample size, quantitative parasitology, aggregated distribution

Received: April 28, 2017; Accepted: June 29, 2017; Published online: July 26, 2017


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