A wide range of potential research designs will be covered in the chapters that follow. They can be categorized roughly into either experimental or nonexperimental strategies. Experimental methods involve research in which participant actions are limited or in some way constrained by the controlled manipulation of variables determined by the researcher. Ideally, experiments should be characterized by random assignment, a procedure used to place participants by chance alone into the different conditions, which enables strong inferences of causality. Quasi-experimental methods are a variant of experimental methods lacking in random assignment, but as in experiments, participants are exposed to some form of variable manipulation imposed by the researcher. For example, we might be interested in the effects of National Merit Scholarships on college performance. Obviously, a researcher cannot randomly assign high school seniors to receive a Merit scholarship or not because of ethical concerns and the fact that receipt of the award is determined by scores on a test. Quasi-experimental methods ( Chapter 10 ) are an attempt to make inferences about possible variables responsible for the outcome differences between recipients and nonrecipients of the scholarship, and to disentangle the effects of the scholarship from other variables such as intelligence or work ethic.