Table 1. Definitions outcome measurements.

Definition bias	Formula	Ref.
Median difference	md eGFR-mGFR	[67,120]
Median percentage difference*	md ((eGFR-mGFR)/mGFR) x 100%	[120]
Mean difference	1/n x Σ (eGFR-mGFR)	[135]
Mean percentage difference ‡	1/n x Σ ((eGFR-mGFR)/mGFR) x 100%	[142]
Precision	Formula	Ref.
Inter quartile range (IQR) difference	IQR of (eGFR—mGFR)	[67]
IQR percentage difference*	IQR of ((eGFR-mGFR)/mGFR) x 100%	[67]
Limits of agreement (LOA)	Mean difference ± 1.96 SD	[135,136]
Standard deviation difference (SD)	σ of all the individual differences	[67,135]
Accuracy	Formula	Ref.
Pk §	Percentage of estimates within k% of mGFR	[67]
Median absolute percentage error (mAPE)	md ((|eGFR—mGFR|)/mGFR) x 100%	[142]
Mean absolute percentage error (MAPE)	1/n x Σ ((|eGFR—mGFR|)/mGFR) x 100%	[142]

* Preferred definition because a relative scale provides a more relevant metric.

^‡ In some articles the mean percentage difference was called the mean percentage error (MPE).

^§ Preferred definition of accuracy. We limited our search to P₁₀, P₂₀, P₃₀ and P₅₀.