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Introduction

In certain scenarios, the odds ratio (OR) provides an unbiased estimate of the rate ratio in case control studies.). 2- 4 Given the value of the baseline risk and the estimate of the OR, the RR can be estimated by the use of a formula. 3, 5 However, the formula may be inconvenient and cumbersome for readers and users of epidemiological information. A nomogram is a graphical calculator that is a useful and convenient way to perform common calculations without the need to remember formulae. The use of the Bayes' nomogram 6 has simplified the use of diagnostic test information 7- 8 and is now frequently used by physicians who may be unaware of the formula involved in the conversion. In this editorial, we show that the Bayes' nomogram, typically associated with likelihood ratios, can also be used to calculate the RR given the OR and the baseline risk.

Degree of divergence between odds ratios (ORs) and relative risks (RRs)*

*NA = not available (ie, not calculable).
The table lists the ORs corresponding to various RRs and baseline risks. Notice that as the baseline risk increases, and as the RR is further from 1, the degree of divergence between the OR and the RR increases. Regardless of the magnitude of the RR, the OR is always further from 1 than the RR.

Relative risk

Baseline risk

0.5

0.75

2

4

5%

0.49

0.74

2.11

4.75

10%

0.47

0.73

2.25

6.0

20%

0.44

0.70

2.67

16.0

50%

0.33

0.60

NA

NA

70%

0.23

0.47

NA

NA

Journals reviewed for this issue*

*Approximately 60 additional journals are reviewed. This list is available on request.

Acta Obstet Gynecol Scand Age Ageing Am J Cardiol Am J Med Am J Obstet Gynecol Am J Psychiatry Am J Public Health Am J Respir Crit Care Med Ann Emerg Med Ann Intern Med Ann Surg Arch Dis Child Arch Gen Psychiatry Arch Intern Med Arch Neurol

Arch Pediatr Adolesc Med Arch Surg Arthritis Rheum BJOG BMJ Br J Gen Pract Br J Psychiatry Br J Surg CMAJ...

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