Groups of 20 snails were held for periods of 1, 2, 3 or 4 weeks in carefully controlled conditions of temperature and relative humidity. There were two species of snail, A and B, and the experiment was designed as a 4 by 3 by 4 by 2 completely randomized design. At the end of the exposure time the snails were tested to see if they had survived; the process itself is fatal for the animals. The object of the exercise was to model the probability of survival in terms of the stimulus variables, and in particular to test for differences between species.
The data are unusual in that in most cases fatalities during the experiment were fairly small.
snailsThe data frame contains the following components:
Speciessnail species A (1) or B (2).
Exposureexposure in weeks.
Rel.Humrelative humidity (4 levels).
Temptemperature, in degrees Celsius (3 levels).
Deathsnumber of deaths.
Nnumber of snails exposed.
Venables, W. N. and Ripley, B. D. (2002) Modern Applied Statistics with S-PLUS. Fourth Edition. Springer.