Background: Updating the Cochrane Reviews is part of the mission of the Cochrane Collaboration. Reviewers are expected to update their reviews at least every 2 years. A preliminary analyses in 1998 suggested that this is not done.

Objective: To find out if Cochrane reviews are updated or not.

Methods: The date fields of the cover sheets of all reviews of the Cochrane Library 2002 Issue 1 were extracted and analysed.

Results: More that 95% of all reviews were edited within the last 2 years (see table).

Date of most recent amendment Date of most recent substantial amendment
rr. of reviews year nr. of reviews year
7 1994
23 1995
45 1996
74 1997
1 1998 124 1998
45 1999 246 1999
117 2000 363 2000
1105 2001 386 2001

All reviews had valid 'date of most recent amendment' and a 'date of most recent substantial amendment' fields. The other dates recommended in the Appendix 2a of the Reviewers Manual are not used: 2 out of 3 reviews (867/1268) do not provide any of: date new studies sought but none found, date new studies found but not yet included/excluded, date new studies found and included/excluded, date reviewers' conclusions section amended.

Interpretation: It appears that 95% of the reviews are amended as expected. However, since Review Manager 4 was introduced in 1999 and most reviews do not provide procedural dates, two interpretations are possible:

- reviewers update the reviews regulary but forget to document their procedure
- the reviews were not updated but only imported into Revman4 or edited insignificantly.

The question of the analysis could not be answered.

Conclusions: A strategy to assure the use of the procedural date fields in the cover sheet should be deviced. Without those fields it is impossible to decide if a review was updated or only edited.