What is random assignment, and what is the difference between random assignment and random selection?
Random assignment is the strongest of all of the experimental control techniques; by randomly forming groups, the groups will be probabilistically equated on all known and unknown variables at the start of the experiment. As you can see, this is very powerful. Random selection is very different from random assignment. The purpose of random selection is to generate a sample that represents a larger population. The purpose of random assignment is to take a sample (usually a convenience sample) and randomly divide it into two or more groups that represent each other. Using a mirror metaphor, in random sampling, we want to sample to mirror the population, but in random assignment we simply want the different groups to mirror one another. By the way, in experimental research, random assignment is much more important than random selection; thats because the purpose of an experiment to establish cause and effect relationships. 9.5. How does random assignment accomplish the goal of controlling