The Government is committed to improving central and local government efficiency and effectiveness, and in times of constrained public finances it is even more important to ensure that public funds are spent on activities that provide the greatest possible economic and social return. This requires that policy is based on reliable and robust evidence, and high quality evaluation is vital to this. HM Treasury's Green and Magenta Books together provide detailed guidelines, for policy makers and analysts, on how policies and projects should be assessed and reviewed. The two sets of guidance are complementary: the Green Book emphasising the economic principles that should be applied to both appraisal and evaluation, and the Magenta Book providing in-depth guidance on how evaluation should be designed and undertaken. The risk of not evaluating, or of poor evaluation, is that policy makers are not aware if policies are ineffective or, worse still, result in overall perverse, adverse or costly outcomes. If there is no good evaluation evidence to demonstrate it, then we cannot be confident that taxpayers' money is being properly spent, even where policies are in reality highly effective. The knowledge we gain from good evaluation can be used to increase policy effectiveness and is essential in informing the development of new policies to achieve the best results.
This revision of the Magenta Book shifts emphasis away from the "analyst's manual" of the previous edition, to a broader guidance document aimed at both analysts and policy makers at all levels of government, both central and local. The new guidance recognises evaluation's place at the heart of policy development, and emphasises that the ability to obtain good evaluation evidence rests as much on the design and implementation of the policy as it does on the design of the evaluation. This gives policy makers much more of the responsibility for securing good evidence than was previously the case. However, this new responsibility need not bring with it significantly greater burdens for policy makers. The revised Magenta Book demonstrates that relatively minor adjustments in policy implementation can greatly improve the ability to obtain high quality evaluation evidence.
The Treasury is grateful for the significant contributions by policy makers and analysts working across Government and elsewhere to the development of this edition of the Magenta Book. Particular gratitude is due to those who participated in the consultation process and provided such detailed and valuable comments.