The Connection Assault on transfer. Before the refinement of analysis of variance was introduced into the analysis of experimental data researchers simply compared the performance of groups given different treatments. A key notion is that of a control group, for without at least one point of reference or contrast the description of an experimental group's performance must be quite limited. The use of a control group in educational research was popularized by Edward I. Thorndike, who in a series of experiments begun in 1900 with Robert S. Woodworth attempted to show the limitations of transfer of training (Clifford, 1968/1984, pp. 270-276). They found, for example, that practice in judging the sizes of rectangles of various dimensions did not improve one's ability to judge the size of a triangle.