On counting and counting errors.

Counting objects in histological sections is often a necessary, sometimes an unexpected part of a research project. The recent literature shows that the subject of counting is of particular interest to readers of the Journal of Comparative Neurology but that it is also contentious and difficult. Even a brief review of past issues of the Journal shows that there are many misconceptions about counting and that there remain issues that have received little or no attention. Counts are subject to many errors. Some reports include readily recognizable errors, others fail to include all of the information that is needed for an evaluation of their accuracy. This review is above all a plea for adequate information about the methods used for counts in all publications. It serves to help those who are new to quantitative methods in histology; it considers some of the basic issues arising for anyone undertaking counts, or reviewing manuscripts that include counts. In particular, it considers recently introduced or re-introduced counting methods that depend on accurate measures along the axis perpendicular to the plane of the sections, and looks at the difficulties inherent in these measures. Copyright 2002 Wiley-Liss, Inc.