To most people, "development" is best measured by the quantity of change — like gains in average income, life expectancy or years spent in school. The Human Development Index (HDI), a composite measure of national progress that my office at the United Nations Development Program oversees, combines all three statistics to rank countries relative to one another.

What many do not realize, however, is that such metrics, while useful, do not tell the entire story of development. In fact, to understand how developed a country is, we must also grasp how people's lives are affected by progress. And to understand that, we must consider the quality of the change that is being reported.

When statisticians compare countries, they require commensurate data. To compare school attendance, for example, researchers would count the number of registered students in each country, relative to all school-age children (although even this can be a challenge in many developing countries, where record keeping is not always standardized).