Figure 3

Fieller's confidence interval. Panel A-D show the figure provided by FCI for examples A-D, respectively. In each figure the red continuous line is the estimate standard curve and the two black dashed curves are the estimated limits of its 100(1-α)% prediction interval. A horizontal line parallel to the X-axis is drawn at the height of the mean of the ct values (y0) measured in the unknown sample. Where this line intercepts the two dashed curves, as well as the standard curve, three perpendicular lines are traced onto the X-axis giving the lower and the upper 100(1-α)% confidence limits (X.lower and X.upper) of the unknown concentration together with its estimate (X0).