The assessment covers the research that was conducted in the period 2008-2014, as well as the research strategies that were outlined for the 2015-2020 period. In this sense the assessment was both retro- and prospective. You can view the full report here. The chapter about TI starts at p. 81.
The committee refrained from giving scores to TI (in contrast to the assessed universities) but had rated Tinbergen Institute very high. We quote: “The structure and content of the TI programmes fully adhere to excellent international standards. (p. 83)”
The committee also concludes that TI’s conferences, seminars, workshops, lectures, publications are at a world-class level (…) (p.84).
The international review committee was chaired by Professor Arie Kapteyn (currently Director of the Center for Economic and Social Research (CESR) at the University of Southern California); other members were Giuseppe Bertola, Raymond De Bondt, Matthias Jarke, George Gelauff, Jan Olhager, David Otley, John Saunders, Henri Servaes, and Edward Snape.