Fig. 3: Protocol for calculating the ND50 for serum by PRNT assay using Probit analysis in R.

a, Plaque counts should be limited to the average of the VOC counts. b, Counts should be arranged in a new worksheet, as shown, and saved as a .csv file. c, Following analysis using the R script supplied, a graph is generated and automatically saved as an .EMF file. d, An example of a good result with a full curve and tight confidence intervals. e, An example of a graph generated for a nonneutralizing sample with a poor curve.