Bias was assessed as the median of the difference between measured GFR and estimated GFR, and precision was assessed as the interquartile range for the difference.3 (link),13 (link) Accuracy was assessed as the root-mean-square error and as the percentage of estimates that differed by more than 30% from the measured GFR (1 – P30) or by more than 20% (1 – P20). Confidence intervals were calculated by means of bootstrap methods (2000 bootstraps).14 The significance of the differences among equations was determined with the use of the signed-rank test for bias, the bootstrap method for the interquartile range and root-mean-square error from the 2000 bootstrap samples, and McNemar’s test for 1 – P30 and 1 – P20.
We evaluated the use of the new equations for the classification of chronic kidney disease in the external-validation population by means of the net reclassification index statistic.15 (link) We compared the proportion of participants who were reclassified as having a measured GFR that was less than 60 ml per minute per 1.73 m2 or greater than or equal to 60 ml per minute per 1.73 m2 on the basis of the new equations versus the CKD-EPI creatinine equation for the overall population and for subgroups according to age, sex, diabetes status, body-mass index, and a creatinine-based estimated GFR of 30 to 89, 45 to 74, 60 to 74, and 45 to 59 ml per minute per 1.73 m2. We performed similar analyses for reclassification based on a measured GFR of 90, 75, 45, 30, and 15 ml per minute per 1.73 m2. Analyses were performed with the use of R, version 2.9.2 (R Development Core Team), and SAS, version 9.2 (SAS Institute), software.
We evaluated the use of the new equations for the classification of chronic kidney disease in the external-validation population by means of the net reclassification index statistic.15 (link) We compared the proportion of participants who were reclassified as having a measured GFR that was less than 60 ml per minute per 1.73 m2 or greater than or equal to 60 ml per minute per 1.73 m2 on the basis of the new equations versus the CKD-EPI creatinine equation for the overall population and for subgroups according to age, sex, diabetes status, body-mass index, and a creatinine-based estimated GFR of 30 to 89, 45 to 74, 60 to 74, and 45 to 59 ml per minute per 1.73 m2. We performed similar analyses for reclassification based on a measured GFR of 90, 75, 45, 30, and 15 ml per minute per 1.73 m2. Analyses were performed with the use of R, version 2.9.2 (R Development Core Team), and SAS, version 9.2 (SAS Institute), software.
