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Table 1 Results of studies quantifying the frequency of data extraction errors

From: Frequency of data extraction errors and methods to increase data extraction quality: a methodological review

Study Studies included (reviews) Measure Result
Carroll 2013 [16] 8 (3) Selection (outcome 1) 17% (review 1 vs. reference standard); 8% (review 2 vs. reference standard)
Selection (outcome 2) 42% (review 1 vs. reference standard); 25% (review 2 vs. reference standard)
Selection (outcome 3) 21% (review 1 vs. reference standard); 25% (review 2 vs. reference standard)
Inaccuracy (outcome 1) 8% (review 1 vs. reference standard); 8% (review 2 vs. reference standard)
Inaccuracy (outcome 2) 17% (review 1 vs. reference standard); 13% (review 2 vs. reference standard)
Inaccuracy (outcome 3) 13% (review 1 vs. reference standard); 8% (review 2 vs. reference standard)
Difference in meta-analysis (outcome 1) RR 1.70 (reference standard) / RR 1.71 (review 1)
Difference in meta-analysis (outcome 2) RR 0.85 (reference standard) / RR 0.87 (review 1) / RR 0.80 (review 2)
Difference in meta-analysis (outcome 3) RR 0.38 (reference standard) / RR 0.40 (review 1)
Gøtzsche 2007 [8] 54 (random selected; 27 meta-analysis) Difference in SMD >0.1 of at least 1 of the 2 included trials 63%
20 (10 meta-analysisa) Difference in SMD >0.1 of pooled effect estimate. 70%
Jones 2005 [17] NR (34) Errors (all types) 50%
Correct interpretation 23.3%
Impact on results All data-handling errors led to changes in the summary results, but none of them affected review conclusionsb
Tendal 2009 [15] 45 (10 meta-analysis) Difference in SMD because of reviewer disagreements < 0.1 53%
  Difference in SMD because of reviewer disagreements < 0.1 (pooled estimates) 31%
  1. a: meta-analyses at least including one erroneous trial; bauthor statement (no quantitative measures provided); ns no significant differences; NR not reported, RD relative difference, RS reference standard, SMD standardized mean difference