Rebecca is interested in how solving different types of puzzles influences creativity. She will have participants try four different puzzles (word, 3-D, 2-D, and number) and measure creativity after each puzzle. To prevent order effects, Rebecca will sort participants into groups and have each group do the puzzles in a different sequence. The first sequence will be word, 3-D, 2-D, number; while the second will be 3-D, 2-D, number, word; and so forth, until each possible condition falls in each position in the experiment. What technique has Rebecca used to prevent order effects?