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NEWS ROUNDUP:
Roger Dobson
Fewer boys born in New York after 9/11 attacks
BMJ 2006; 333: 516-b [Full text]
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[Read Rapid Response] Unchanged sex ratio in New York after 9/11 attacks
Stian Lydersen   (24 January 2007)

Unchanged sex ratio in New York after 9/11 attacks 24 January 2007
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Stian Lydersen,
Professor, medical statistics
Norwegian University of Science and Technology, N-7006 trondheim, Norway

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Re: Unchanged sex ratio in New York after 9/11 attacks

The bmj.com news roundup on 9 September 2006 includes the headline “Fewer boys born in New York after 9/11 attacks”, accompanied by a dramatic photo of the attack. (BMJ 2006;333:516 (9 September), doi:10.1136/bmj.333.7567.516-b). The background is an article by Catalano et al. (Human Reproduction 2006 21(12):3127-3131; doi:10.1093/humrep/del283)

However, a closer look at their data shows that their conclusion is misleading and based on inappropriate statistical methods (Human Reproduction, doi:10.1093/humrep/del475). In the years before 11 September 2001, New York City experienced a sex ratio equal to 1.051 (number of boys to the number of girls, among live-born singletons). Catalano et al. computed the sex ratio for each of the 10 four week periods succeeding 11 September 2001. But they focus only on the P-value (= 0.02) for the one period (1-28 January 2002) with the lowest sex ratio (0.9995) among such periods. They fail to adjust for the fact that there are several candidate periods. In fact, the sex ratio over the 3 periods they hypothesize is 1.042 (P-value = 0.49), and the sex ratio over the 40 weeks is 1.052 (P- value = 0.86). The observed sex ratios are as expected from before the event.

Unfortunately, the misleading news about reduced sex ratio has been quoted in medical journals and mass media around the world. The attack on 11 September 2001 has had many adverse results. But there has been no change in the human sex ratio in New York City. Misleading sensational news like this can make matters worse than they are and create unnecessary fear.

Competing interests: None declared