On the topic of online learning, there is a steady stream of studies, but many of them focus on limited issues or lack control groups. The Education Department report said that it had identified more than 1,000 empirical studies of online learning that were published from 1996 through July 2008. For its conclusions, however, the Education Department considered only a small number (51) of independent studies that met strict criteria. They had to contrast an online teaching experience to a face-to-face situation, measure student learning outcomes, use a "rigorous research design," and provide adequate information to calculate the differences.