thermore, although the results support a correlation betweenwork-hours restrictions and improved patient outcomes, nocausal relationship is established.

e HOW QUICKLY DO SYSTEMATIC REVIEWS GOOUT OF DATE? A SURVIVAL ANALYSIS. Shojania KG,Sampson M, Ansari MT, et al. Ann Intern Med 2007;147:224 –33.

The goal of this Canadian study was to determine theaverage amount of time from publication of a systematic re-view to the point where changes in evidence are sufficientlyimportant to warrant updating the review. Types of reviewsused included randomized or quasi-randomized controlled tri-als that evaluated a drug, class of drug, medical device, orprocedure. Quantitative and qualitative signals for updating areview were employed. Quantitative signals consisted ofchanges in statistical significance or a relative change in effectmagnitude of at least 50%. Qualitative signals included newinformation about harm that was sufficient to affect clinical

decision-making, important caveats to the original results,emergence of a superior alternate therapy, and importantchanges in certainty or direction of effect. The study showedthat the median time before an update signal appeared was 5.5years, and in 23% of reviews a signal appeared within 2 years.Reviews involving cardiovascular medicine, and those with ahigh degree of heterogeneity in the original review had theshortest time to update signal. The researchers conclude that, inlight of the fact that signals for the update of systematic reviewsoccur frequently and within a relatively short time, authorsshould consider updating their reviews if the submission topublication time is prolonged. Otherwise, reviews run the riskof being already outdated at the time of initial publication.

[Emily Johnston, MD,

Denver Health Medical Center, Denver, CO]

Comment: This study serves as a reminder to the clinicianthat systematic reviews are not perfect and require a critical eyeto be of value to the reader. Furthermore, systematic reviewsolder than 5 years should be considered out of date.

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