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Application Of Experimental Design Term Paper

¶ … limiting a researcher's view of the problem are situational factors that can skew the results of her experiment, i.e., effects of pretesting, social threats, and group differences (Trochim, 2008, 188). External factors, such as possible sample size, can limit even the type of testing available to the researcher. As such, researchers have come up with a number of different types of designs over the years. This essay will compare and contrast two of these; experimental and quasi-experimental designs. "Experimental designs are often touted as the most rigorous of all research designs" (Trochim, 2008, 186). What is so rigorous about them is that they are the strongest type of design in regards to their internal validity (Trochim, 2008, 186). This is because the basic form of the experimental design uses random assignment, or chance to group participants. In effect, this makes the two groups, if selected from...

This enables the researcher to actually "calculate the chance that the two groups will differ just because of the random assignment (that is, by chance alone)" (Trochim, 2008, 189).
The way that experimental designs control internal validity so well is a function of their structure. A simple experimental design called a two-group, posttest-only, randomized design uses random assignment to create two groups; one in which treatment is offered (for example), and one that receives no treatment at all. Posttesting is then performed. If the treatment group shows a different outcome than the no-treatment group, we might be able to conclude that the different outcome was a result of the treatment. We are confident in the experiment's internal validity because, since groups were assigned randomly, we know that the difference in…

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Why would a researcher, who values internal validity, then choose a quasi-experimental design, that specifically lacks in internal validity? The reason is that experimental designs are not always the most effective. They're subject to social threats of internal validity, and have difficulties with external validity (Trochim, 2008, 188). An experimental design is "intrusive and difficult to carry out in most real-world contexts," and is basically an "artificial situation" created to "assess [a] causal relationship with high-internal validity." Resultingly, there are difficulties in generalizing the findings to the real world.

Alternatively, certain types of quasi-experimental designs are some "of the most intuitively sensible designs around" (Trochim, 2008, 210). This is because random selection is often not logical or possible. For example, say we wanted to understand the effects of a certain type of treatment on both developmentally disabled adults and adults that were not developmentally disabled. Random selection, or an experimental design, would be impossible here, because we already have our two groups; they're dictated by the difference.

The basic reasons one might choose an experimental design or a quasi-experimental design has to do with, I think, resources, and what exactly is being tested. I feel that there is no design that is "better" or "worse" -- applying those labels would not make any sense at all here, because every experiment has a different aim. What is good for one experiment may be bad for another. The most important thing, I feel, is simply to have an understanding of both, and the ability to employ each when necessary.
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