Optimizing the sampling scheme for a stereological study: how many individuals, sections, and probes should be used.

Stereology provides meaningful quantitative descriptions of the geometry of three-dimensional (3D) structures from measurements that are made on two-dimensional (2D) images. A pilot stereological study will provide information that can be used to rationalize how many individuals, sections, and probes should be used to ensure that one is sampling enough, but not too much, to achieve the goal of a study. This general approach is exemplified in the thought experiment described here, which involves a comparison of the means of estimates of the total number of neurons N in two groups, using the simplest of statistical tests, the Student's t-test. It is also applicable to studies involving other estimates of total quantities such as volume, surface, and length obtained from a parallel series of sections.