The Commitment to Development Index (CDI) ranks the 21 richest countries on their commitment to policies that benefit poor nations.

These 21 countries are the richest, most developed countries in the world, leaving out tiny nations such as Iceland and Luxembourg. Along with Luxembourg, they constitute the full membership of the Organization for Economic Cooperation and Development's Development Assistance Committee (OECD-DAC), which is the official organization of aid donors.

The CDI is maintained by the Center for Global Development and published in Foreign Policy magazine each year. CGD staff and outside collaborators designed and collected data for the seven individual components. David Roodman is manager and chief architect. He also designed the aid component and, in 2005, revised the trade component, building on the work of CGD Senior Fellow William Cline.

Helping poor countries is about more than aid. We chose major policy areas that support the development of poorer countries and for which reasonable data was available. The list of policy areas is:

• Aid, which funds initiatives such as childhood immunization; new roads;
• Trade, which gives industries in poor countries access to larger markets and creates jobs;
• Investment, which can be a source of capital and good management practices;
• Migration, which lets workers seek higher-paying jobs in rich countries and send earnings back home;
• Environment, which underscores the point that rich and poor nations are tied together by the shared use of resources;
• Security, which is a prerequisite for development; and
• Technology, since innovation is a critical factor in development.

Yes and no. The CDI is intended to inspire a race to the top, so "winners" should be proud of their achievements. Yet there is room for improvement in all rich countries. Almost all countries score below average in at least one area and most are below average in at least three.

It is difficult to know whether a one-point increase in a country's aid score would be better for development than a one-point increase in its trade score. And the potential benefits--perhaps a new school in Malawi, or more jobs for wheat farmers in Argentina--are hard to compare to one another. Therefore, we chose equal weighting. All seven areas matter.

The Index assesses policy effort rather than impact. The United States and Japan give more aid in absolute terms, but they are among the least generous once the size of their economies is taken into account. The top-scoring countries give a lot of aid in proportion to their gross domestic product and their population, and/or have relatively low trade barriers and/or generate relatively little pollution, and so on.

Each component of the CDI combines many numbers into a single score, placing that score on a standard scale, so that 5 represents average performance by the standards of the first index year, 2003. This makes it easy to see that Japan's policies, for instance, are above-average on investment (with a 5.6 in 2006), but not as strong on security (2.8) by the standards of Japan's peers. If a country is twice as good as average, it scores a 10, and if it's more than twice as good, it scores above 10. That happened to Austria on migration. The opposite is true for the environment and trade components. Scores on environmental pollution and trade barriers start at 10 (no emissions or barriers) and go down from there. A country may be able to power through the 10-point ceiling by giving more aid or admitting more immigrants, but it could fall to zero when it comes to its ranking for the excessive amount of pollution it emits or for the high tariffs it imposes.

Most of the data come from official sources such as the United Nations, the World Bank, the Organization for Economic Co-operation and Development (OECD), and the United Nations, or from academic researchers. CGD and its collaborators also collect information country by country for parts of the aid, migration, investment components.

As a relatively objective way to decide which military interventions should be counted, the security component of the CDI only includes contributions to interventions approved by international bodies such as the U.N. Security Council, NATO, and African Union. Since the U.S.-led invasion of Iraq had no such mandate, it is not counted.