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Logo of bmjThis ArticleThe BMJ
BMJ. 2007 May 19; 334(7602): 1020.
PMCID: PMC1871789
β Blockers

Misuse of confidence intervals threatens conclusions

Christopher J Cates, general practitioner

The data presented in table 1 of Ong's review leave considerable uncertainty about whether atenolol is better or worse than other β blockers.1 The confidence intervals for the results on other β blockers are wide (as fewer patients have been studied), and the test for interaction shows that the relative risk for atenolol, compared with other β blockers, for stroke is 1.05 (95% confidence interval 0.26 to 4.17), for myocardial infarction 1.22 (0.91 to 1.63), and for total mortality 1.21 (0.95 to 1.14). All of these confidence intervals include the possibility of no difference, and for stroke the results are compatible with atenolol being four times better or four times worse than other β blockers. It is very misleading to draw conclusions based on whether significance is achieved with either treatment alone.2


Competing interests: None declared.


1. Ong HT. β blockers in hypertension and cardiovascular disease. BMJ 2007;334:946-9. (5 May.) [PMC free article] [PubMed]
2. Altman DG, Bland JM. Interaction revisited: the difference between two estimates. BMJ 2003;326:219. [PMC free article] [PubMed]

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