There are many animal species whose population numbers bring them to the attention of resource agencies and others; e.g., Greater sage-grouse, Oregon spotted frog, Lahontan cutthroat trout. Some of these species are listed under the ESA, others are not; in both cases accurate estimates of population size and limiting factors are critical for informed policy and management decisions. Correctly measuring population size and the factors affecting it is not always obvious because of the data formats and mathematical formulation of the statistical models.
Biological data are counts of individuals, integers not fractions. While data summaries often present a fractional mean (2.4 children per family) it is more realistic and accurate to use the median value (a whole number) with the same number of values both less and greater than it.