In the chart above, each dot represents a country. The curve shows the general tendency with which prosperity increases as GDP per capita increases. Its shape is fitted to all 149 countries covered by the Prosperity Index. If a country falls below the curve, then we can say that compared to all other countries, it is under-delivering prosperity for its citizens. That is, it has a prosperity deficit: its level of prosperity is lower than we would expect given its wealth. Likewise, if a country rises above the curve, then we can say that it is over-delivering prosperity for its citizens: it has a prosperity surplus.
More than absolute prosperity scores or rankings alone, the Prosperity Gap shows the Prosperity Index to be a tool for change. It provides leaders with the assessment they need to transform their nation into a more prosperous one and it provides citizens with the information they need to hold those leaders to account.