The field has grown substantially since the late 20th century, for example by the development of methods, surveys and indices to measure happiness and related concepts,  • _____, 2005. "The Economics of Happiness: Insights on Globalization from a Novel Approach," "World Economics", 6(3), pp. 41–58 (indicated there as adapted from previous source).  • David G. Blanchflower, 2008. "Happiness Economics," "NBER Reporter Online", (2), pp. 7–10. Abstract-linked-footnotes version.</ref> as well as quality of life. Happiness findings have been described as a challenge to the theory and practice of economics. Nevertheless, furthering gross national happiness, as well as a specified Index to measure it, has been adopted explicitly in the Constitution of Bhutan in 2008, to guide its (economic) government.