Intended for healthcare professionals

Rapid response to:

Clinical Review

Recent developments in obstetrics

BMJ 2003; 327 doi: (Published 11 September 2003) Cite this as: BMJ 2003;327:604

Rapid Response:

Positive predictive value

The author states that: "Positive predictive values are similar in
both high and low risk groups, so 20% of women with an abnormal Doppler
result will develop pre-eclampsia." This statement seems to violate Bayes'
theorem that positive predictive value increases as pretest probability
increases. Do other readers understand how this is possible?

Competing interests:  
None declared

Competing interests: No competing interests

13 September 2003
Peter S. Millard, MD, PhD
Family Practice Residency Program
Bangor, Maine, USA