Figure 4

Calibration for low level DNA quantification. Base: All valid observations. The figure shows mean values at each concentration with a) (filled circles ●) negative observations excluded; b) (open circles o) all values including negative observations taken as Ct = 55 (the means coincide at log₁₀(C)>0.5). Regression lines are the exclusion-by-sample regression (solid line), the line through means with negative observations excluded (dashed line) and the line through means with negative observations set to Ct = 55 (dotted line).