Grading in histopathology

Grading is the process of subdividing a diagnostic category to increase the amount of information in a histopathology report and so assist clinicians in making individual therapeutic decisions. A good grading system will have a high signal to noise ratio with good inter- and intra-observer agreement. Many grading systems in histopathology have been produced by a top-down design process which does not take into account the natural distribution of cases. Such systems may produce very poor results if the arbitrary boundaries of the grading system do not coincide with the natural boundaries of clusters of cases. This review examines the fundamental processes involved in grading and demonstrates bottom-up design processes which have the potential to produce effective grading systems.