A common element in all experiments is the deliberate manipulation of an assumed cause followed by an observation of the effects that follow. A quasi-experiment is an experiment that does not uses random assignment of participants to conditions.An inus condition is an insufficient but non-redundant part of an unnecessary but sufficient condition. It is insufficient, because in itself it cannot be the cause, but it is also non-redundant as it adds something that is unique to the cause. It is an insufficient cause.Most causal relationships are non-deterministic. They do not guarantee that an effect occur, as most causes are inus conditions, but they increase the probability that an effect will occur. To different degrees, all causal relationships are contextually dependent.A counterfactual is something that is contrary to fact. An effect is the difference between what did happen and what would have happened. The counterfactual cannot be observed. Researchers try to approximate the counterfactual, but it is impossible to truly observe it.Two central tasks of experimental design are creating a high-quality but imperfect source of counterfactual and understanding how this source differs from the experimental condition.Creating a good source of counterfactual is problematic in quasi-experiments. There are two tools to attempt this:Observe the same unit over timeMake the non-random control groups as similar as possible to the treatment groupA causal relationship exists if the cause preceded the effect (1), the cause was related to the effect (2) and there is no plausible alternative explanation for the effect other than the cause (3). Although quasi-experiments are flawed compared to experimental studies, they improve on correlational studies in two ways:Quasi-experiments make sure the cause precedes the effect by first manipulating the presumed cause and then observing an outcome afterwards.Quasi-experiments allows to control for some...