Fig. 4

Residuals versus predicted values for the formulas of Mercuriali/ Lisander (same formula, so long as no blood is transfused; RBC loss in mL) (a), Gross, Bourne, Meunier and Ward (blood loss in mL) (b) and for the new formula presented here (Hb loss in g) (c). The significant slope of all formulas in a and b is apparent, indicating systematic underestimation of small and overestimation of large blood loss, as well as the mean of residuals for all formulas is markedly below zero, i.e. in the mean, blood loss is systematically underestimated by all these formulas. By contrast, the mean value of residuals and the gradient with the new formula (c) are zero, i.e. the predicted Hb loss is equally precise and accurate throughout the entire range of observations