Ratio measures in leading medical journals: structured review of accessibility of underlying absolute risks

doi:10.1136/bmj.38985.564317.7C

BMJ 2006;333:1248 (16 December), doi:10.1136/bmj.38985.564317.7C (published 23 October 2006)

Research

Ratio measures in leading medical journals: structured review of accessibility of underlying absolute risks

Lisa M Schwartz, associate professor of medicine¹, Steven Woloshin, associate professor of medicine¹, Evan L Dvorin, instructor of medicine², H Gilbert Welch, professor of medicine¹

¹ Veteran Affairs Outcomes Group, White River Junction, VT 05009, USA, ² Dartmouth Medical School, Hanover, NH

Correspondence to: S Woloshin steven.woloshin{at}dartmouth.edu

Objective To examine the accessibilityof absolute risk in articles reporting ratio measures in leadingmedical journals.

Design Structured review ofabstracts presenting ratio measures.

Setting Articles published between1 June 2003 and 1 May 2004 in Annals of Internal Medicine, BMJ,Journal of the American Medical Association, Journal of theNational Cancer Institute, Lancet, and New England Journal ofMedicine.

Participants 222 articles basedon study designs in which absolute risks were directly calculable(61 randomised trials, 161 cohort studies).

Main outcome measure Accessibilityof the absolute risks underlying the first ratio measure inthe abstract.

Results 68% of articles (150/222)failed to report the underlying absolute risks for the firstratio measure in the abstract (range 55–81% across thejournals). Among these articles, about half did report the underlyingabsolute risks elsewhere in the article (text, table, or figure)but half did not report them anywhere. Absolute risks were morelikely to be reported in the abstract for randomised trialscompared with cohort studies (62% v 21%; relative risk 3.0,95% confidence interval 2.1 to 4.2) and for studies reportingcrude compared with adjusted ratio measures (62% v 21%; relativerisk 3.0, 2.1 to 4.3).

Conclusion Absolute risks areoften not easily accessible in articles reporting ratio measuresand sometimes are missing altogether—this lack of accessibilitycan easily exaggerate readers' perceptions of benefit or harm.

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