Figure 2

Illustration of the Newcombe method. Method from Newcombe [13], using the spreadsheet available from http://medicine.cf.ac.uk/primary-care-public-health/resources/. In [13], the difference in probability of correct diagnosis is plotted against lambda. Here the relationship of lambda to prevalence is shown in figure A), and the difference in probability of correct management is shown against prevalence in figures B)-F) for different values of R; blue lines show 95% confidence interval. R is the ratio of importance of false negatives (c1) to the importance of false positives (c2), i.e. R = c1/c2 (Table 4). At prevalence = 0 the difference is equal to the difference in the NMR between the enhanced and control groups, and at prevalence = 1 the difference is equal to the difference in PMR between the two strategies.