ReseaRch MethoD 38 experiments Experiments measure the effect that an action has on a situation by demonstrating a causal relationship or determining conclusively that one thing is the result of another. experiments can determine cause and effect by meeting three conditions: the presence of two observable and measurable actions or events; the cause event occurring before effect; and elimina- tion of all other possible causes. 1 In a typical experiment, a hypothesis is posed, the exposure to something is manipulated for some participants while held constant for others, and the effect is measured and compared between the two groups, keeping all other conditions of the experiment exactly the same. The independent or experimental variable is the variable that is manipulated. This can be as simple as something that participants are exposed to (such as a new design), or may be varied in terms of level of exposure (for example, length of time). The dependent variable is then measured to see if there is a significant difference between those exposed to the manipulation, and those not. An operational definition is necessary to define exactly how the dependent variable is being measured. Is a "better" input device, for example, defined by performance speed on a particular task, or a subjective assessment of ergonomic comfort? Ideally participants are randomly assigned to either an experimental or control group. The experi- mental group, or treatment group, consists of participants who are exposed to manipulations of the 1. Sommer, robert, and Barbara Sommer. a practical Guide to behavioral research: tools and techniques. new York: oxford University Press, 2002. 2. larson, Adam M., and lester C. loschky. "The Contributions of Central versus Peripheral vision to Scene Gist recognition." Journal of Vision 9, no. 10 (2009): 1­16. Further Reading Hanington, Bruce. "relevant and rigorous: Human-Centered research and design education." design issues 26, no. 3 (Summer 2010): 18­26.