Assessing bias in GFR estimating equations: improper GFR stratification can yield misleading results

Assessing bias (estimated – measured) is key to evaluating glomerular filtration rate (GFR). Stratification by subgroups can indicate where equations perform differently. However, there is a fallacy in the assessment of two instruments (e.g., eGFR and mGFR) when stratifying on the level of only one of those instruments. Here, we present statistical aspects of the problem and a solution for GFR stratification along with an empirical investigation using data from the CKiD study. Compared and contrasted biases (eGFR relative to mGFR) with 95