Comparison between 1973 and 2004/2016 WHO grading systems in patients with Ta urothelial carcinoma of urinary bladder.

From a statistical standpoint, it appears that the 2004/2016 WHO grading system holds a small, although measurable advantage over the 1973 WHO grading system. Other considerations, such as intraobserver and interobserver variability may represent an additional matric to consider in deciding which grading system is better.