1. In Reply to ‘Newer GFR Estimating Equations Require Validation in Different Populations’ 
Andrew S. Levey, MD, Hocine Tighiouart, MS, Andrew L. Simon, ScM, Lesley A. Inker, MD, MS 
American Journal of Kidney Diseases 
Volume 70, Issue 4, Pages (October 2017)
DOI: /j.ajkd
Copyright © 2017 National Kidney Foundation, Inc. Terms and Conditions

2. Figure 1
Performance of creatinine–cystatin C equations in the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) cystatin C validation database (n=1,119). Bias is assessed as the median difference between measured (mGFR) and estimated GFR (eGFR). The difference is expressed as mGFR minus eGFR. A positive value indicates that eGFR is an underestimate of mGFR. Precision is assessed as the interquartile range (IQR) of the difference between mGFR and eGFR. A larger value indicates lesser precision. Accuracy is influenced by both bias and precision. Accuracy is assessed as the percentage of large errors (1 − P30, the percentage of participants in whom the difference between eGFR and mGFR is >30% of mGFR) and root mean square error (RMSE, estimates the residual of the observed from predicted values; on the log scale, it approximates the standard deviation of the percent error in estimation). Larger values indicate lesser accuracy. Confidence intervals were calculated by bootstrap methods (2,000 bootstraps) for median difference and IQR of the differences and by the binomial method for P30. Bold font indicates nonoverlapping confidence intervals compared to CKD-EPI. This method is more conservative than identifying differences with P<0.05, which we believe is more appropriate given the large sample size and multiple hypothesis tests. Green highlighting indicates better performance compared to CKD-EPI. Red highlighting indicates worse performance than CKD-EPI. Analyses were computed using SAS Enterprise Guide (version 7.12). Abbreviations: LMR, Lund Malmö revised; FAS, full-age spectrum.
American Journal of Kidney Diseases  , DOI: ( /j.ajkd )
Copyright © 2017 National Kidney Foundation, Inc. Terms and Conditions