Indexes, which distill large amounts of information into a few numbers, appear to be gaining popularity among policy advocates and researchers. This CGD Essay tells the story of one such, the Commitment to Development Index, and draws lessons for others who would also devise indexes. The CDI rates 21 rich countries on how much their government policies help or hurt poorer nations. It has been reasonably successful on the goals of raising awareness of certain ideas, in particular that helping is about more than aid, and embodying and communicating the mission of an institution, the Center for Global Development.
Among the lessons: To work well, policy indexes must combine humility with a clear sense of purpose. They must incorporate judicious trade-offs between considerations that range from philosophy to mathematics to science to communications strategy. Outreach is at least as important as design. The Web in particular allows outreach to serve multiple audiences, with detail for those who want it, and overviews for those who do not. Perhaps the greatest design challenge is the tension between the desire for simplicity, and the complexity of policy, which can turn an index into a black box. A suite of materials, paper and electronic, written at different levels of detail may not eliminate this problem, but can reduce it to the point where the index can have an impact.
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