BIOSTATISTICAL APPROACHES TO ASSESSMENT 135
Table 7.6. 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
2
0
0
0
0
0
0
0
0
0
0
4
67
45
30
20
14
9
6
4
3
2
6
88
66
46
31
20
13
8
5
3
2
8
95
78
57
38
24
14
8
5
3
1
10
98
86
65
43
27
15
8
4
2
1
12
100
96
84
65
45
28
16
8
4
2
14
100
98
87
67
45
27
14
7
3
1
16
100
99
94
80
59
38
21
11
5
2
18
100
100
95
81
59
36
19
9
4
2
20
100
100
98
89
70
46
26
13
5
2
22
100
100
98
89
69
44
24
11
4
2
24
100
100
99
94
77
53
30
14
6
2
26
100
100
100
96
84
61
36
17
7
2
28
100
100
100
96
83
58
33
15
6
2
30
100
100
100
98
88
65
38
18
7
2
32
100
100
100
98
87
63
36
16
5
2
34
100
100
100
99
90
69
41
19
7
2
36
100
100
100
99
93
74
46
21
8
2
38
100
100
100
99
93
72
43
19
6
2
40
100
100
100
100
95
77
47
22
7
2
42
100
100
100
100
96
81
52
24
8
2
44
100
100
100
100
96
79
49
22
7
2
46
100
100
100
100
97
83
53
24
8
2
48
100
100
100
100
98
86
57
27
9
2
50
100
100
100
100
99
88
61
30
10
2
Note:
Rounded to nearest percent. Test statistic is observed Poisson-distributed count of cases in exposed group. Nominal probability of 2.5% in lower tail.