Variation in penicillin testing
Six samples of penicillin were tested using the B. subtilis plate method on each of 24 plates. The response is the diameter (mm) of the zone of inhibition of growth of the organism.
The data are described in Davies and Goldsmith (1972) as coming from an
O.L. Davies and P.L. Goldsmith (eds), Statistical Methods in Research and Production, 4th ed., Oliver and Boyd, (1972), section 6.6
str(Penicillin) dotplot(reorder(plate, diameter) ~ diameter, Penicillin, groups = sample, ylab = "Plate", xlab = "Diameter of growth inhibition zone (mm)", type = c("p", "a"), auto.key = list(columns = 3, lines = TRUE, title = "Penicillin sample")) (fm1 <- lmer(diameter ~ (1|plate) + (1|sample), Penicillin)) image(fm1@L, sub = "Structure of random effects interaction in penicillin model")