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 ds

ws



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 = Σsdsws = -.003 with a standard error .022. We define ε(max)s = max((1 - π0s)/π1s, (1 - π1s)/π0s), where πzs equals one minus the fraction missing in group z and stratum s. The anticipated maximum bias is ψmax Σs ε(max)s ws = ± .10 ψmax, where ψmax 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

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