How to average microbial densities to characterize risk

In the past, the geometric mean, or less frequently the arithmetic mean, has been used as a summary descriptor of microorganism densities in waters and other environmental media. It is shown in this paper that, if the interest is characterizing the risk from organisms that are described by either an exponential dose-response relationship, or a dose-response relationship that is linear at low doses, the appropriate summary descriptor is the arithmetic mean. Therefore, in future work, authors should be encouraged to report data on such organisms using this summary descriptor.