CRD's original guidance for undertaking systematic reviews was first published in 1996 and revised in 2001. The guidance is widely recommended and used both nationally and internationally. Although the main principles behind systematically reviewing research evidence remain the same, various aspects of review methodology have continued to develop at such a pace that a third edition is warranted.
The purpose of the new edition remains to provide practical guidance for undertaking evidence synthesis based on a thorough understanding of systematic review methodology. It presents the different stages of systematic reviewing and has been expanded to incorporate issues specific to reviews of diagnostic and prognostic tests, public health interventions, adverse effects and economic evaluations. Effectiveness continues to be the focus, but in addition information relating to questions about `how' and `why' is included, recognising that health care decision making often involves complex questions that go beyond `does it work'?
