Table 2

Results of Polyp Prevention Trial

stratum s

adenoma

difference in observed

weight

bias factor ε_(max)s

stratum s

recurrence

rates of recurrence d_s

w_s

sex

age

group

no

yes

missing

control

573

374

94 (9%)

study

578

380

76 (7%)

men

30–49

control

33

22

5 (8%)

-.23

.07

.09

study

58

12

3 (4%)

40–59

control

99

76

7 (4%)

.01

.17

.05

study

94

76

9 (5%)

60–69

control

122

105

25 (10%)

-.04

.23

.11

study

144

105

18 (7%)

70–79

control

65

76

26 (16%)

-.04

.13

.20

study

70

71

29 (17%)

women

30–49

control

54

11

3 (4%)

.03

.10

.07

study

47

12

4 (6%)

40–59

control

69

24

4 (4%)

.02

.11

.04

study

69

27

4 (4%)

60–69

control

77

31

13(11%)

.08

.12

.11

study

68

40

5 (4%)

70–79

control

54

29

11(12%)

.22

.07

.12

study

28

37

4 (6%)

The overall estimate of the difference in probabilities of recurrence between study and control groups is = Σ_sd_sw_s = -.003 with a standard error .022. We define ε_(max)s = max((1 - π_0s)/π_1s, (1 - π_1s)/π_0s), where π_zs equals one minus the fraction missing in group z and stratum s. The anticipated maximum bias is ψ_max Σ_s ε_(max)s w_s = ± .10 ψ_max, where ψ_max is the anticipated bias if there were complete confounding of the unobserved covariate and treatment.

Baker and Freedman BMC Medical Research Methodology 2003 3:8   doi:10.1186/1471-2288-3-8