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Table 4 Simulated true relative risks (RR's) for multiple physical symptoms and PTSD for a range of hypothesised true prevalence rates. The calculations are based on Stang's algorithm (using an iterative approach to obtain the true RR's).

From: How many mailouts? Could attempts to increase the response rate in the Iraq war cohort study be counterproductive?

Outcome

True prevalence (%)

True RR

Multiple symptoms:

 

13.22% error

6.5% error

Observed prevalence 10.84%

6

3.05

1.48

Observed RR 1.22

8

2.15

1.41

 

10

1.83

1.35

 

12

1.65

1.31

 

14

1.52

1.28

 

16

1.44

1.26

PTSD

   

Observed prevalence 3.90%

3

N/A

5.5

Observed RR 1.09

4

N/A

1.64

 

5

N/A

1.35

 

7

N/A

1.18

 

9

N/A

1.12

 

11

1.90

N/A

 

13

1.25

N/A

 

15

1.16

N/A

  1. * N/A indicates that the true prevalence for this row is not compatible with the specified error rate
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BMC Medical Research Methodology

ISSN: 1471-2288

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