1) I tried to show that by presenting conditional probablities using
natural frequencies (ie numbers) what appears to be a confusing
calculation becomes simple. Why complicate the obvious? Bad presentation
of medical risks leads to misunderstanding and poor decision taking. [1]
2) The situation described "What would you tell a woman who tested
positive in a screening mammogram that her chances were of having breast
cancer?" should never occur. A woman must be told this before she consents
to screening. Consent is only valid if it is fully informed. [2]
Information must also include a clear explanation of the balance of
harms and benefits, including overdiagnosis and overtreatment. Techniques
to do this are well established. [3,4]
3) Demystification of diagnostic testing is not difficult. [5]
Rapid Response:
Simple arithmetic
Three points arise.
1) I tried to show that by presenting conditional probablities using
natural frequencies (ie numbers) what appears to be a confusing
calculation becomes simple. Why complicate the obvious? Bad presentation
of medical risks leads to misunderstanding and poor decision taking. [1]
2) The situation described "What would you tell a woman who tested
positive in a screening mammogram that her chances were of having breast
cancer?" should never occur. A woman must be told this before she consents
to screening. Consent is only valid if it is fully informed. [2]
Information must also include a clear explanation of the balance of
harms and benefits, including overdiagnosis and overtreatment. Techniques
to do this are well established. [3,4]
3) Demystification of diagnostic testing is not difficult. [5]
Dr John Doherty
(dr.johndoherty@gmail.com)
References
1) Gigerenzer G, Edwards A, Simple tools for understanding risks:
from innumeracy to insight. BMJ 2003; 327 : 741 doi:
10.1136/bmj.327.7417.741
2) Baines CJ. Mammography screening: are women really giving informed
consent? J Natl Cancer Inst 2003;95:1508-1511.
3) Schwartz LM, Woloshin S, Welch HG. Risk communication in clinical
practice: putting cancer in context. J Natl Cancer Inst Monogr. 1999; 124-
33.
4) Paling J. Strategies to help patients understand risks. BMJ 2003;
327:745doi:10.1136/bmj.327.7417.745
5) Perera R, Heneghan C, Making sense of diagnostic tests likelihood
ratios. Evid Based Med 2006;11:130-131 doi:10.1136/ebm.11.5.130-a
Competing interests: No competing interests