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Mutagenesis Advance Access originally published online on April 2, 2008
Mutagenesis 2008 23(3):171-182; doi:10.1093/mutage/gen015
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© The Author 2008. Published by Oxford University Press on behalf of the UK Environmental Mutagen Society. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org.

Statistical issues in the use of the comet assay

David P. Lovell* and Takashi Omori1

Department of Biostatistics, Postgraduate Medical School, University of Surrey, Daphne Jackson Road, Manor Park, Guildford, Surrey GU2 7WG, UK 1Department of Biostatistics, Kyoto University School of Public Health, Onogawa 16-2, Tsukuba, Japan

The comet or single-cell gel electrophoresis assay is now widely used in regulatory, mechanistic and biomonitoring studies using a range of in vitro and in vivo systems. Each of these has issues associated with the experimental design which determine to a large extent the statistical analyses than can be used. A key concept is that the experimental unit is the smallest ‘amount’ of experimental material that can be randomly assigned to a treatment: the animal for in vivo studies and the culture for in vitro studies. Biomonitoring studies, being observational rather than experimental, are vulnerable to confounding and biases. Critical factors in any statistical analysis include the identification of suitable end points, the choice of measure to represent the distribution of the comet end point in a sample of cells, estimates of variability between experimental units and the identification of the size of effects that could be considered biologically important. Power and sample size calculations can be used in conjunction with this information to identify optimum experimental sizes and provide help in combining the results of statistical analyses with other information to aid interpretation. Interpretation based upon the size of effects and their confidence intervals is preferred to that based solely upon statistical significance tests. Statistical issues associated with the design and subsequent analyses of current validation studies for the comet assay include the identification of acceptable levels of intra- and inter-laboratory repeatability and reproducibility and criteria for dichotomizing results into positive or negative.

* To whom correspondence should be addressed. Tel: +44 1483 688609; Fax: +44 1483 688501; Email: d.lovell{at}surrey.ac.uk

Received on October 19, 2007; revised on February 6, 2008; accepted on February 18, 2008.


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