We have used 35 reliable datasets which measure how countries affect the world outside their own borders: there are five of these in each of seven categories, covering the big issues like education, science, war and peace, trade, culture, health, censorship, the environment, freedom, etc. Most of these datasets are produced by the United Nations system and other international agencies, and a few by NGOs and other organisations.
These datasets are combined into a common measure which gives an overall ranking, a ranking in each of the seven categories, and a balance-sheet for each country that shows at a glance how much it contributes to the world and how much it takes away. The performance indicators are measured per GDP dollar, to correct for the size of each country's economy, and create a level playing field.
More technically, countries receive scores on each indicator as a fractional rank (0=top rank, 1=lowest) relative to all countries for which data is available. The category rankings are based on the mean fractional ranks on the 5 indicators per category (subject to maximum 2 missing values per category). The overall rank is based on the average of the category ranks.