Quasi-experiment January 29, 2023 a quasi-experiment

Internal validity
Internal validity is the approximate truth about inferences regarding cause-effect or causal relationships. This is why validity is important for quasi experiments because they are all about causal relationships. It occurs when the experimenter tries to control all variables that could affect the results of the experiment. Statistical regression, history and the participants are all possible threats to internal validity. The question you would want to ask while trying to keep internal validity high is "Are there any other possible reasons for the outcome besides the reason I want it to be?" If so, then internal validity might not be as strong.^[8]
External validity
External validity is the extent to which results obtained from a study sample can be generalized "to" some well-specified population of interest, and "across" subpopulations of people, times, contexts, and methods of study.^[13] Lynch has argued that generalizing "to" a population is almost never possible because the populations to which we would like to project are measures of future behavior, which by definition cannot be sampled.^[14] Therefore, the more relevant question is whether treatment effects generalize "across" subpopulations that vary on background factors that might not be salient to the researcher. External validity depends on whether the treatments studies have homogeneous effects across different subsets of people, times, contexts, and methods of study or whether the sign and magnitude of any treatment effects changes across subsets in ways that may not be acknowledged or understood by the researchers.^[15] Athey and Imbens and Athey and Wager have pioneered machine learning techniques for inductive understanding of heterogeneous treatment effects.^[16][17]
Design types
"Person-by-treatment" designs are the most common type of quasi experiment design. In this design, the experimenter measures at least one independent variable. Along with measuring one variable, the experimenter will also manipulate a different independent variable. Because there is manipulating and measuring of different independent variables, the research is mostly done in laboratories. An important factor in dealing with person-by-treatment designs are that random assignment will need to be used in order to make sure that the experimenter has complete control over the manipulations that are being done to the study.^[18]
An example of this type of design was performed at the University of Notre Dame. The study was conducted to see if being mentored for your job led to increased job satisfaction. The results showed that many people who did have a mentor showed very high job satisfaction. However, the study also showed that those who did not receive the mentor also had a high number of satisfied employees. Seibert concluded that although the workers who had mentors were happy, he could not assume that the reason for it was the mentors themselves because of the numbers of the high number of non-mentored employees that said they were satisfied. This is why prescreening is very important so that you can minimize any flaws in the study before they are seen.^[19]
"Natural experiments" are a different type of quasi-experiment design used by researchers. It differs from person-by-treatment in a way that there is not a variable that is being manipulated by the experimenter. Instead of controlling at least one variable like the person-by-treatment design, experimenters do not use random assignment and leave the experimental control up to chance. This is where the name "natural" experiment comes from. The manipulations occur naturally, and although this may seem like an inaccurate technique, it has actually proven to be useful in many cases. These are the studies done to people who had something sudden happen to them. This could mean good or bad, traumatic or euphoric. An example of this could be studies done on those who have been in a car accident and those who have not. Car accidents occur naturally, so it would not be ethical to stage experiments to traumatize subjects in the study. These naturally occurring events have proven to be useful for studying posttraumatic stress disorder cases.^[18]