1. One or more computer-readable storage devices storing computer-executable instructions that, when executed by a processor of a computing device, configure the processor to perform acts comprising: drawing a set of items from an overall population, the set of items including a first sub-population and a second sub-population; sampling the set of items from the overall population; calculating a first precision value and a first variance value for the set of items from the first sub-population, and a second precision value and a second variance value for the set of items from the second sub-population; calculating an overall confidence value for the overall population based at least in part on the first variance value, the second variance value, a desired confidence value, and a confidence estimate value; and determining if the overall confidence value satisfies an overall confidence condition, the overall confidence condition comprising a standard error for the overall population being less than or equal to a predetermined ratio, wherein the predetermined ratio includes a predetermined difference from a target value over a predetermined confidence value.