Standard curves based on the four-parameter log-logistic model (FCT) fitted using the four alternative approaches to treat background noise (BKG) in the four emulated datasets.

The dashed lines represent the confidence interval of the curve, and the green line represents the geometric mean of the blank controls. RS = R-square. (A) Standard curve fitted using “Ignore” background noise method; (B) standard curve fitted including the background noise as an extra point when fitting the curve, using “Include” background method; (C) standard curve fitted subtracting the background noise using the “Subtract” method; (D) standard curve fitted constraining the lower asymptote to the background noise using the “Constraint” method.