The leaves within the small box are pretreated with a certain dose of fungicide. A standard series of 10 such small boxes consists of one without fungicide, and nine with a geometric sequence of doses from, e.g., 0.001 to 10. Each series thus gives rise to 10 outcome variables measuring the growth for the 10 doses. The values should generally decline.
Routine analysis performs, for each series, a probit analysis with a logarithmic scale for the dose.
It attributes maximal random variation for doses around ED50. In data of the type described, random variation is maximum for low doses. We use a suitably adjusted model and estimate parameters by maximum likelihood. These factors clearly affect the sensitivity a . The slope b is essentially constant over genotypes.