Figure 4

Modelling the mapping of fluorescence responses to concentration values.

(a) A Simulations of mapping a hypothetical fluorescence response (Fl) distribution to concentration values (pg/ml) through a sigmoidal curve. (a) Gives the concentration response curve (sigmoidal curve), the corresponding inverse sigmoidal curve and the input fluorescence distribution. Note, the log2(Fl) responses are normalized to lie between 0 and 1. The boxplots overlaid on the sigmoidal curve show the relative fluorescence range/scale of the input distribution at low (0.05), middle (0.5; EC50 response) and high (0.95) responses levels against the concentration curve (for comparison see Supplementary Fig. S1). The dashed horizontal and vertical lines on the sigmoidal and the inverse curve respectively highlight these levels. (b) Shows the corresponding output concentration distributions after mapping the input distribution in (a) to pg/ml when the input distribution is centred at low, middle, or high log2(Fl) responses. The vertical dashed lines overlaid on the output distributions represent the expected mean concentration as obtained from the input mean fluorescence response. (c) Simulations of mapping the log2(Fl) responses from two hypothetical tissues A and B to pg/ml is given. Three input distribution pairs that differ only with respect to their level of skewness (0, −5 and 5 respectively). The distance between the input means in each pair was set to achieve a Cohen’s effect size of 0.8. (d) Gives the resulting p-values obtained from two-sample t-tests on the output concentration distributions, as the input distributions (c) are mapped to concentration values from low (0.05) to high (0.95) response levels; step size approx. 0.01 log2(Fl) units. Note, the expected p-values in (d) represent the results obtained from t-tests on the input fluorescence distributions after each translation along fluorescence axis.