Figure 5

Logistic regression of detection probability. Logistic regression of a) (solid line) p(positive) vs. concentration C with false negative at log₁₀(C) omitted; b) (dashed line) p(positive) vs. log₁₀(C) with false negative included. Solid points show fraction of positives at each concentration with the false negative omitted; the open circle shows the calculated fraction at log₁₀(C) with the false negative included. The apparent lower limit to the solid curve is an artefact of plotting on the log₁₀ axis.