The Human Development Index (HDI), in use by the United Nations since 1990, aims to measure economic progress using metrics, such as Gross National Income, human well-being factors such as life expectancy, and level of education. HDI changes as a combination of these three factors. Norway has had the world’s highest HDI since 2007, with only Canada, Japan and Iceland having also held the top spot in some years. The Inequality HDI (IHDI) is an adjusted version of the measure, developed as one part of the 2010 Human Development Review, with equality as its focus. The IHDI is considered a more reliable measure than HDI, which becomes skewed with increased inequality while IHDI is not. Skew reduces the accuracy of the measurement. However, HDI is still considered useful as a measure of potential human development.