## Abstract

Mutagenicity in the Ames assay is evaluated by comparing the number of revertants observed in treated cultures to those in untreated cultures. Often, some form of the '2-fold rule' is employed, whereby a compound is judged mutagenic if a 2-fold or greater increase is seen in a treated culture. In order to understand the underpinnings of this approach, we study some of its statistical properties. We assume that the number of revertants on any plate from a given two-group experiment follows a Poisson distribution and we address the following questions: (1) what is the false-positive error probability of observing at least a doubling of the number of colonies from the control to the treatment group?; (2) if a given mean number of colonies is postulated for a control group, what number of colonies above the observed control mean provides a false-positive rate of 5%? We also present results for question 1 in the case where the number of revertants follows a negative binomial distribution.

Original language | English (US) |
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Pages (from-to) | 23-31 |

Number of pages | 9 |

Journal | Mutation Research - Genetic Toxicology |

Volume | 369 |

Issue number | 1 |

DOIs | |

State | Published - Jul 10 1996 |

## Keywords

- Ames
- Background
- Bacterial
- False-positive error
- Mutation
- Negative binomial distribution
- Poisson distribution
- Spontaneous

## ASJC Scopus subject areas

- Toxicology
- Genetics