The Cochrane Collaboration: international activity within Cochrane Review Groups in the first decade of the twenty-first century.

The Cochrane Collaboration (http://www.cochrane.org) is the world's largest organisation dedicated to preparing, maintaining and promoting the accessibility of systematic reviews of the effects of healthcare interventions. It is an international organisation with participants in more than 100 countries, principally focused around the Cochrane Review Groups that are responsible for the preparation and maintenance of Cochrane reviews. Since 2000, a periodic audit has been done to count the number of active members in the Cochrane Review Groups, subdivided by the countries in which these people are based. At the beginning of 2010, there were almost 28,000 people involved, an increase from about 5500 in 2000. The growth of activity has been dramatic, and especially large for authors of Cochrane reviews and protocols. In the year 2000, 2840 people were listed as authors by the Cochrane Review Groups. At the beginning of 2010, this had risen to over 21,000 people.