Evid Based Nurs 9:36-37 doi:10.1136/ebn.9.2.36
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Reporting of weighted event rates in Evidence-Based Nursing abstracts of systematic reviews

  1. Stephen R Werre, PhD1,
  2. Cindy Walker-Dilks, MLS1,
  3. Andrew Jull, RN, MA (Appl)2
  1. 1McMaster University, Hamilton, Ontario, Canada
  2. 2Clinical Trials Research Unit, University of Auckland, New Zealand

      Evidence-Based Nursing publishes many abstracts of systematic reviews. In these abstracts, we try to the report the results in a consistent format—ie, in a table that includes weighted event rates for intervention and control groups, relative risk reductions (or increases), and numbers needed to treat (or to harm). If you have ever tried to check these calculations using the data reported in the original review, you may have puzzled over our reporting of intervention event rates. Take a look, for example, at the abstract and table of the systematic review by Gafter-Gvili et al1,2 on p50. This review assessed the effectiveness of antibiotic prophylaxis for patients with neutropenia. One of the analyses compared the effects of fluoroquinolones (intervention) and placebo or no intervention (control) on infection related mortality. In our abstract table, you will see that 1.9% of patients who received fluoroquinolones had deaths related to infection compared with 6.9% of patients who received placebo or no intervention. The data from the original review are shown below in figures 1 and 2. You can quickly add up the number of events for each group and divide by the total number of patients: the event rate for the control group is 33/480 or 6.9%, same as in the abstract table; the event rate for the fluoroquinolone group is 14/542 or 2.6%—different from the 1.9% reported in the abstract table. Is this a typo or did someone make an error? The answer is …

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