Van Praag estimated the WFI for thousands of individuals in most countries of Western Europe.
He enriched his research by adopting the satisfaction question module used by modern happiness economists.
His main new results are the application of happiness economics with Barbara Baarsma to estimate shadow prices of airplane-noise hindrance near Amsterdam Airport, which method may be used for estimating the shadow prices of other external effects as well and the development of a two-layer model with Frijters and Ferrer-i-Carbonell, where life satisfaction is seen as an aggregate of domain satisfactions.
He published in 2004 the comprehensive monograph Happiness Quantified, a Satisfaction Calculus Approach (with Ada Ferrer-i-Carbonell), which was revised in 2008 and translated into Chinese in 2010.
He is a regular contributor to the Dutch dailies NRC Handelsblad and de Volkskrant and the professional weekly Economisch-Statistische Berichten.
Van Praag is a Fellow Emeritus of the European Economic Association, member of the Royal Netherlands Academy of Arts and Sciences (Koninklijke Nederlandse Academie van Wetenschappen) since 1999,[6] elected as a member of the International Statistical Institute, member of the Royal Dutch Society of Sciences (Koninklijke Hollandsche Maatschappij van Wetenschappen), Fellow of CESifo Munich, IZA Bonn, DIW Berlin, AIAS Amsterdam, Honorary Fellow and chairman–founder (1986) of the Tinbergen Institute.