Good but bittersweet news for fans of The Americans. The hit FX drama series, which focuses on Russian spies living undercover as Americans in the 1980s, is currently in its fourth season, with three more episodes to go, and FX has renewed the critically acclaimed show for not one but two more seasons!
Experiments that take advantage of natural occurrences are quasi-experiments, for example, comparing achievement level of first-born children with that of later-born children; or comparing student performance at two schools, one of which has a lower student-teacher ratio.
The third type of experiment is the observational experiment, which is used when there is no way to control variables. These types of experiments happen outside of the laboratory and may be called a non-experimental method. Just like the quasi-experimental type of method, there is a great deal of effort made to identify all variables that may be influential on the variable of interest.