SNAILS
Data:
Species Exposure Rel.Hum Temp Deaths N
1 A 1 60.0 10 0 20
2 A 1 60.0 15 0 20
3 A 1 60.0 20 0 20
4 A 1 65.8 10 0 20
5 A 1 65.8 15 0 20
6 A 1 65.8 20 0 20
7 A 1 70.5 10 0 20
8 A 1 70.5 15 0 20
9 A 1 70.5 20 0 20
10 A 1 75.8 10 0 20
11 A 1 75.8 15 0 20
12 A 1 75.8 20 0 20
13 A 2 60.0 10 0 20
14 A 2 60.0 15 1 20
15 A 2 60.0 20 1 20
16 A 2 65.8 10 0 20
17 A 2 65.8 15 1 20
18 A 2 65.8 20 0 20
19 A 2 70.5 10 0 20
20 A 2 70.5 15 0 20
21 A 2 70.5 20 0 20
22 A 2 75.8 10 0 20
23 A 2 75.8 15 0 20
24 A 2 75.8 20 0 20
25 A 3 60.0 10 1 20
26 A 3 60.0 15 4 20
27 A 3 60.0 20 5 20
28 A 3 65.8 10 0 20
29 A 3 65.8 15 2 20
30 A 3 65.8 20 4 20
31 A 3 70.5 10 0 20
32 A 3 70.5 15 2 20
33 A 3 70.5 20 3 20
34 A 3 75.8 10 0 20
35 A 3 75.8 15 1 20
36 A 3 75.8 20 2 20
37 A 4 60.0 10 7 20
38 A 4 60.0 15 7 20
39 A 4 60.0 20 7 20
40 A 4 65.8 10 4 20
41 A 4 65.8 15 4 20
42 A 4 65.8 20 7 20
43 A 4 70.5 10 3 20
44 A 4 70.5 15 3 20
45 A 4 70.5 20 5 20
46 A 4 75.8 10 2 20
47 A 4 75.8 15 3 20
48 A 4 75.8 20 3 20
49 B 1 60.0 10 0 20
50 B 1 60.0 15 0 20
51 B 1 60.0 20 0 20
52 B 1 65.8 10 0 20
53 B 1 65.8 15 0 20
54 B 1 65.8 20 0 20
55 B 1 70.5 10 0 20
56 B 1 70.5 15 0 20
57 B 1 70.5 20 0 20
58 B 1 75.8 10 0 20
59 B 1 75.8 15 0 20
60 B 1 75.8 20 0 20
61 B 2 60.0 10 0 20
62 B 2 60.0 15 3 20
63 B 2 60.0 20 2 20
64 B 2 65.8 10 0 20
65 B 2 65.8 15 2 20
66 B 2 65.8 20 1 20
67 B 2 70.5 10 0 20
68 B 2 70.5 15 0 20
69 B 2 70.5 20 1 20
70 B 2 75.8 10 1 20
71 B 2 75.8 15 0 20
72 B 2 75.8 20 1 20
73 B 3 60.0 10 7 20
74 B 3 60.0 15 11 20
75 B 3 60.0 20 11 20
76 B 3 65.8 10 4 20
77 B 3 65.8 15 5 20
78 B 3 65.8 20 9 20
79 B 3 70.5 10 2 20
80 B 3 70.5 15 4 20
81 B 3 70.5 20 6 20
82 B 3 75.8 10 2 20
83 B 3 75.8 15 3 20
84 B 3 75.8 20 5 20
85 B 4 60.0 10 12 20
86 B 4 60.0 15 14 20
87 B 4 60.0 20 16 20
88 B 4 65.8 10 10 20
89 B 4 65.8 15 12 20
90 B 4 65.8 20 12 20
91 B 4 70.5 10 5 20
92 B 4 70.5 15 7 20
93 B 4 70.5 20 9 20
94 B 4 75.8 10 4 20
95 B 4 75.8 15 5 20
96 B 4 75.8 20 7 20
Description:
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 data are unusual in that in most cases fatalities during the experiment were fairly small.
Format:
- Species
snail species A (1) or B (2).
- Exposure
exposure in weeks.
- Rel.Hum
relative humidity (4 levels).
- Temp
temperature, in degrees Celsius (3 levels).
- Deaths
number of deaths.
- N
number of snails exposed.
Task:
Model the probability of survival in terms of the stimulus variables, and in particular to test for differences between species.