However, Progresa/Oportunidades is lauded not so much as for its modest cost as for the fact that it works. It has been subject to one of the most rigorous randomized trials of any public proverty program in the world. The Washington-based International Food Policy Research Institute (IFPRI), with many affiliated researchers, has intensively studied the program, using a variety of methods. The most convincing evidence comes from the way the program was initially rolled out. Only some communities were to take part in the program at first, before it reached full scale, and the order in which initially targeted communities were included was randomized. Data were collected from both initially included and excluded families, so that the impact of the program could be studied independently of the many possible confounding factors that can otherwise distort the results of an evaluation. Participants in these rigorous studies have included some of the world's leading development micro-economists.