Wednesday, April 8, 2009

Twins, Aging, and the Logic of the MSS Design

One useful way to get a sense of the logic upon which the MSS--"most similar system--design is based is to consider differences between identical twins. Obviously, twins share the widest range of similarities that two human beings (units of analyses; "systems") can share: in this regard, they are almost perfect examples of two "most similar systems." Yet, for the most part, twins do not develop exactly alike: over time, differences invariably crop up. These differences--such as "aging"--can be identified as dependent variables: an outcome or phenomenon that is the product of some other factor or set of factors. With this in mind, consider the picture of two "identical" twins (above), one of whom appears much older than the other. The difference tells us that something caused one twin to age faster than the other. Thus, the task of the researcher is to focus on finding out what other differences may have caused or resulted in one twin appearing older than the other. These other differences are the independent variable(s). The task, to put it in slightly different terms, is to find key differences in a sea of similarities. Click here to read an article in Time Magazine about a study on identical twins.

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