Disagreements in meta-analyses using outcomes measured on continuous or rating scales: observer agreement study.
OBJECTIVE
To study the inter-observer variation related to extraction of continuous and numerical rating scale data from trial reports for use in meta-analyses.


METHODS
Observer agreement study.


METHODS
A random sample of 10 Cochrane reviews that presented a result as a standardised mean difference (SMD), the protocols for the reviews and the trial reports (n=45) were retrieved.


METHODS
Five experienced methodologists and five PhD students independently extracted data from the trial reports for calculation of the first SMD result in each review. The observers did not have access to the reviews but to the protocols, where the relevant outcome was highlighted. The agreement was analysed at both trial and meta-analysis level, pairing the observers in all possible ways (45 pairs, yielding 2025 pairs of trials and 450 pairs of meta-analyses). Agreement was defined as SMDs that differed less than 0.1 in their point estimates or confidence intervals.


RESULTS
The agreement was 53% at trial level and 31% at meta-analysis level. Including all pairs, the median disagreement was SMD=0.22 (interquartile range 0.07-0.61). The experts agreed somewhat more than the PhD students at trial level (61% v 46%), but not at meta-analysis level. Important reasons for disagreement were differences in selection of time points, scales, control groups, and type of calculations; whether to include a trial in the meta-analysis; and data extraction errors made by the observers. In 14 out of the 100 SMDs calculated at the meta-analysis level, individual observers reached different conclusions than the originally published review.


CONCLUSIONS
Disagreements were common and often larger than the effect of commonly used treatments. Meta-analyses using SMDs are prone to observer variation and should be interpreted with caution. The reliability of meta-analyses might be improved by having more detailed review protocols, more than one observer, and statistical expertise.
Tendal
Britta
B
Nordic Cochrane Centre, Rigshospitalet, Dept 3343, Blegdamsvej 9, DK-2100 Copenhagen, Denmark. bt@cochrane.dk
Higgins
Julian P T
JP
Jüni
Peter
P
Hróbjartsson
Asbjørn
A
Trelle
Sven
S
Nüesch
Eveline
E
Wandel
Simon
S
Jørgensen
Anders W
AW
Gesser
Katarina
K
Ilsøe-Kristensen
Søren
S
Gøtzsche
Peter C
PC
D002986:Clinical Trials as Topic / Q000592:standards / Q000706:statistics & numerical data*; D003625:Data Collection; D015201:Meta-Analysis as Topic; D015588:Observer Variation; D012196:Review Literature as Topic
Br J Psychiatry. 2003 Apr;182:303-11
12668405
J Clin Epidemiol. 2006 Jul;59(7):697-703
16765272
PLoS Med. 2009 Jul 21;6(7):e1000097
19621072
Cochrane Database Syst Rev. 2006 Oct 18;(4):CD004510
17054207
Cochrane Database Syst Rev. 2007 Jan 24;(1):CD005160
17253541
Cochrane Database Syst Rev. 2007 Apr 18;(2):CD005333
17443583
Cochrane Database Syst Rev. 2007 Jan 24;(1):CD004716
17253519
Cochrane Database Syst Rev. 2007 Apr 18;(2):CD004585
17443550
Cochrane Database Syst Rev. 2006 Oct 18;(4):CD005179
17054243
Cochrane Database Syst Rev. 2006 Oct 18;(4):CD004350
17054201
Br J Psychiatry. 1998 May;172:420-4
9747404
JAMA. 2004 May 26;291(20):2457-65
15161896
Cochrane Database Syst Rev. 2007 Jan 24;(1):CD005233
17253549
BMJ. 1996 Feb 10;312(7027):345-9
8611831
Br J Psychiatry. 1998 May;172:413-9
9747403
Explore (NY). 2005 Jan;1(1):40-5
16791967
JAMA. 2007 Jul 25;298(4):430-7
17652297
Cochrane Database Syst Rev. 2005 Oct 19;(4):CD003135
16235315
Behav Res Ther. 1998 Oct;36(10):959-70
9714946
Cochrane Database Syst Rev. 2006 Oct 18;(4):CD005473
17054260
Cochrane Database Syst Rev. 2006 Jul 19;(3):CD002870
16855994
J Clin Epidemiol. 2005 Jul;58(7):741-2
15939227