Introduction: evidence, policy and
practice
The role of evidence in public policy making has
been described and explained in widely varying
ways. These range from a direct role for research in
framing policy, and examples of evidence leading
directly to policy change, through to evidence
being considered an optional extra of marginal
relevance—part of a complex process in which
powerful vested interests have the most influence
over policy making. In these circumstances, evidence
is used selectively to justify predetermined
positions that are largely ideologically driven, or
used to achieve tactical advantages over political
opponents.1