matching

Definition:
(see chapter 7)

Notes
Careful matching may approximate randomness in some situations, and in real life, this may be as close to ideal as possible. (Suter 2012, pg. 13)

Careful matching may approximate randomness in some situations, and in real life, this may be as close to ideal as possible.

"less is left to chance when using matching prior to random assignment," meaning that careful selection of matched variables can help ensure that the groups being compared are similar in relevant aspects.
Specifically, it points out that if the matching variable is not related to the posttest measure, then it doesn't contribute to the study's validity. Therefore, researchers often use a pretest version of the posttest measure as the matching variable. This approach helps ensure that the groups are comparable on a key outcome before any treatment is applied, enhancing the reliability of the findings.
In short, effective matching can significantly reduce confounding variables, making it easier to draw valid conclusions from the research. (pg. 10)

Example
A researcher planned to test whether a new method for teaching reading called Read Now! was more effective than one currently in use. To this end, 60 first graders ' reading skills were assessed with a pretest, then rank ordered from most advanced to least advanced. Pairs were formed by coupling the two most advanced, next most advanced, and so on, until the two least advanced were coupled. One member of each pair was randomly assigned to Read Now! while the other was retained as a control. The two groups, now nearly identical ( on average ) in their pretreatment reading ability, were exposed to treatment or control instruction for 12 weeks, followed by a posttest measure of reading achievement. Any posttest difference could hardly be attributed to pretreatment reading differences because they were the same on average. If other extraneous influences ( e.g., teachers ' skill ) are controlled, then the researcher is entitled to conclude that the manipulation ( the true independent variable, in this case the new teaching method Read Now! ) probably caused the difference in the outcome.