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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.