Krantz and Dalal review studies that assess the validity of Web experiments. Whereas laboratory studies typically use a small, homogeneous sample tested in controlled conditions, the Internet study typically uses a large, heterogeneous sample tested in less well-controlled conditions. Krantz and Dalal define validity in terms of the correspondence of results between experiments conducted via the Web and those done in the laboratory. The trend emerging from the early research on this problem is that Internet studies yield the same conclusions as studies done in the lab.