When we think of experimental science, certain things come to mind, such as working in a laboratory or the "scientific method". However, at its core, most of experimental science is based on determining whether differences exist or not. For example, we may be interested in knowing whether the behavior of two species are different or whether patients receiving a drug respond differently than patients that do not. Sometimes we are simply sampling and measuring quantities that vary naturally and looking to see whether groups differ in those quantities, but more often we manipulate a situation and want to know whether the quantity that results from the manipulation is different from the quantity that would result without the manipulation (as in the drug trial example discussed the previous section).
In order to understand how we can assess whether real differences exist, we will expand on the topic that was introduced in the previous section: the role that random variation plays in our ability to detect differences.