Randomization of experimental conditions can be of great value in determining if treatment affects the outcome, so randomization is used frequently in conjunction with cloud seeding experiments. Because cloud seeding is not an emphasis in this course, randomization will not be emphasized here, except to note that it can be used with any of the experimental designs. For example, if a target-control ratio for randomly seeded clouds is compared to a similar ratio for the unseeded clouds, the result is less affected by persistent correlations than is the target-control ratio when all clouds are seeded. An important variation of these designs is the randomized crossover design, in which one of two areas is seeded randomly and the other used as a control area.