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Table 3 Revision rates outcome data reported for THA (n/N) vs HA (n/N) in 3 reviews

From: A case study of binary outcome data extraction across three systematic reviews of hip arthroplasty: errors and differences of selection

Study BMJ Cochrane* HTA Comments
Dorr 1986 [22] 2/39 vs 4/50 2/39 vs 4/50 2/39 vs 4/50 Identical
Skinner 1989 [17] NR 3/80 vs 13/100 4/89 vs 12/91 As Table 1 above, plus an additional error: BMJ calculates 25% rather than the reported 24% for numerator
(1-year data)    
Ravikumar 2000 [18] 6/91 vs 22/89 NR 6/89 vs 22/91
(13-year data)    
Baker 2006 [12] 1/40 vs 6/41 1/40 vs 3/41 1/40 vs 6/41 Selection difference:
BMJ, HTA and Liang [7] all report 1/40 vs 6/41; Cochrane omits 3/41 which were classified as planned or awaiting revision; the event had not taken place but was “planned” only, so was not counted
Keating 2006 [11] NR NR NR Identical
Blomfeldt 2007 [9] 4/60 vs 3/60 1/60 vs 0/60 0/60 vs 0/60 Selection difference:
Cochrane 1/60 is a “revision” described by Blomfeldt as a “wound revision”; only revision of implant counts as a revision in the HTA; the BMJ review figures include re-operations both on the contra-lateral side, not related to the implant, and for trauma of the lower limb. [10]
Macaulay 2008 [23] 1/17 vs 0/23 1/17 vs 0/23 1/17 vs 0/23 Identical
Mouzopoulos 2008 [8] 1/43 vs 3/43 1/43 vs 5/43 1/39 vs 5/38 Selection difference:
Numerators: BMJ “excluded” 2 HA revisions from the analysis (so 3 rather than 5) but this was arguably not justified as the individuals had the outcome of interest and so should have been included;
Denominators: As Table 2.
  3/24 errors =13% 2/24 errors =8%   6 analysed studies =a/B vs c/D =24 variables
6/24 selection differences = 25% 5/24 selection differences = 21%
  1. *Revisions in Cochrane are categorised as “Major reoperations”. Findings are given in bold.
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