136 BIOLOGICAL EFFECTS OF LOW LEVEL EXPOSURES
Table 7.7. Probability of Observing a Significantly Lower Risk in an Exposed Group, by Relative Risk and Expected Number of Cases in the
Exposed Group When the Relative Risk is Unity
Relative Risk
Expected Cases
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
i
o o o o o o o o o o
4
67
45
30
20
14
9
6
4
3
2
6
88
66
46
31
20
13
8
5
3
2
8
99
92
78
60
43
29
19
12
7
4
10
100
95
82
63
44
29
17
10
5
3
12
100
99
93
79
61
42
27
16
9
5
14
100
99
94
80
60
40
24
13
7
3
16
100
100
97
89
72
51
32
18
9
4
18
100
100
98
89
71
48
29
15
7
3
20
100
100
99
94
79
58
36
19
9
4
22
100
100
100
96
85
65
43
24
11
5
24
100
100
100
96
84
63
39
20
9
3
26
100
100
100
98
89
70
45
24
11
4
28
100
100
100
99
92
75
51
28
13
5
30
100
100
100
99
92
73
47
24
10
4
32
100
100
100
99
94
78
52
28
12
4
34
100
100
100
100
96
82
57
31
13
5
36
100
100
100
100
96
80
54
28
11
3
38
100
100
100
100
97
84
58
31
12
4
40
100
100
100
100
98
87
62
34
14
4
42
100
100
100
100
9f?
89
66
37
15
5
44
100
100
100
100
98
88
63
33
13
4
46
100
100
100
100
99
90
67
36
14
4
48
100
100
100
100
99
92
70
39
15
4
50
100
100
100
100
99
94
73
42
17
5
Note:
Rounded to nearest percent. Test statistic is observed Poisson-distributed count of cases in exposed group. Nominal probability of 5% in lower tail.