3. Maturation. Maturation refers to changes that ordinarily occur with time (e.g., strength, increasing knowledge). For instance, let’s say a new method to increase children’s attention span is tested in an experimental intervention. And let’s say that most children are more attentive two months later, during the post-test. The experimenter may think this improvement is the result of the method, but the rival hypothesis is simply that the children became more mature, and THAT increased their attention. To handle the extraneous variable of maturation, researchers use equivalent comparison groups, or us use experimental designs in which the experimental group serves as its own control (e.g., the equivalent time samples design).