In what follows, I want to show you how the power of experimental logic is applied to real research problems. The major experimental designs are shown in figure 4.1. The notation is pretty standard. The letter X stands for some intervention—a stimulus or a


Some research designs.

treatment. R means that participants are randomly assigned to experimental conditions— either to the intervention group that gets the treatment, or to the control group that doesn’t. Several designs include random assignment and several don’t. O stands for ‘‘observation.’’ OJ means that some observation is made at Time 1, O2 means that some observation is made at Time 2, and so on.

‘‘Observation’’ means “measurement of some dependent variable,’’ but as you already know, the idea of measurement is pretty broad. It can be taking someone’s temperature or testing their reading skill. It can also be just writing down whether they were successful at hunting game that day.

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