The Cochrane Collaboration celebrates its 20th Anniver-

Full list of author information is available at the end of the articleBackground Methods for systematic reviews of health interventions have focused mainly on addressing the question of ‘What works? ’ or ‘Is this intervention effective in achie-ving one or more specific outcomes? ’ Systematic reviews have addressed the efficiency of those interventions less often. Yet such questions as ‘Is it worth it?’, ‘At what cost is the outcome achieved?’, and ‘What will be the eco-nomic impact of this intervention? ’ are crucial if health systems are to use the resource they have available to their best advantage. In times of financial austerity, these questions take on particular importance. In his semina