${\sigma }_M$	standard deviation of the prediction error
${\mu }_M$	mean value of the prediction error
$c_1$	edge distance of a single anchor
$d_{nom}$	anchor diameter
$r$	Pearson’s correlation coefficient
$f_c$	is the concrete compressive strength.
$k_{ucr}$	is a product-specific value for non-cracked concrete
$f_{ck,cube}$	is the characteristic compressive strength from 150 mm concrete cube specimens
$f_{cm}$	mean value of concrete compressive cylinder strength
$f_{cc}$	is the mean compressive strength measured at 200 mm concrete cube specimens
$l_f$	is the influence length of the anchor loaded in shear
$k_c$	is equal to the value of 13.5 for metal expansion anchors and bonded anchors
${\alpha }_c$	is equal to the value of 1.0 for an undisturbed uniaxial compression stress state (this occurs for $h_{ef}$ equal to approximately 5 anchor diameters) is equal to the value of 0.8 for anchors within compression zones with cracks developing parallel to the compression direction (this occurs for $h_{ef}$ greater than 5 anchor diameters)
$k_1, k_2, k_3$	are calibration factors
$h_{ef}$	is the anchor embedment depth (the distance of the failure invitation point to the free surface)
$V_{Rm,c}^0$	mean shear breakout resistance
$N$	tensile breakout resistance
$N_{Rm,c}^0$	mean tensile breakout resistance
$N_{Rk,c}^0$	characteristic tensile breakout resistance
$N_{exp,x}$	experimentally observed failure load for a single anchor test $x$ in tension
$X$	represents the input variable set which include the embedment depth $h_{ef}$, anchor $d_{nom}$ and the concrete strength $f_c$
$N_{pred, x}$	represents mean concrete breakout model prediction for the same anchor test $x$