Most quantitative dissertations, whether carried out by academics or undergraduate, master’s or doctoral level students, will involve one of three types of replication, which we refer to as duplication, generalisation or extension.
In most cases, replication is associated with duplication. In other words, you take a piece of published research and repeat it, typically in an identical way to see if the results that you obtain are the same as the original authors. In some cases, you don’t even redo the previous study, but simply request the original data that was collected, and reanalyse it to check that the original authors were accurate in their analysis techniques. However, duplication is a very narrow view of replication, and is partly what has led some journal editors to shy away from accepting replication studies into their journals. The reality is that most research, whether completed by academics or dissertation students at the undergraduate, master’s or doctoral level, involves either generalisation or extension. This may simply be replicating a piece of research to determine whether the findings are generalizable within a different population or setting/context, or across treatment conditions; terms we explain in more detail later in this article. Alternately, replication can involve extending existing research to take into account new research designs, methods and measurement procedures, and data analysis techniques. As a result, we call these different types of replication study: Route A: Duplication, Route B: Generalisation and Route C: Extension.
In reality, it doesn’t matter what you call them. We simply give them these names because (a) they reflect three different routes that you can follow when doing a replication-based dissertation (i.e., Route A: Duplication, Route B: Generalisation and Route C: Extension), and (b) the things you need to think about when doing your dissertation differ somewhat depending on which of these routes you choose to follow. However, it’s worth noting that these three routes are not mutually exclusive, which means that your dissertation could either (a) incorporate elements of all three types or (b) simply follow one of these three routes. For the most part, you’ll take on just one route.
There are a number of reasons why we choose to replicate research, whether we are referring to replication in general, or a specific type of replication (i.e., duplication, generalisation and extension). In a way, you can view these justifications as those that involve checking research in some way, and others that aim to build on previous research:
Checking previous research
There are countless journal articles that have been published, building a vast body of knowledge that we rely on in all walks of life. However, once a piece of research is produced and published, it is rarely replicated. Seldom do researchers check the quality of a previous piece of research. The findings from a study are too often taken-for-granted. Imagine all the knowledge that has accumulated in the world, and all those studies that have built on previous studies that have not even been checked. For this reason, reproducibility is one of the cornerstones of good science (whether in the social or physical sciences). It helps to stop the spread of false knowledge. This is the focus of Route A: Duplication, but is also a part of Route B: Generalisation and Route C: Extension, since these also involve the testing of the findings from the original study that is being replicated.
Building on previous research
Stopping the spread of false knowledge is important, but so is the creation of new knowledge. In this respect, replication is not just about reproducibility and checking, but also using previous studies as a platform to launch the pursuit of new knowledge. This is the focus of Route B: Generalisation and Route C: Extension, which aim to not only test previous findings, but also either see how far they can be generalised (i.e., Route B: Generalisation), or modified and extended in some way (i.e., Route C: Extension). Generalisation is one of the main goals of quantitative research; that is, testing to see whether the findings from the study you are interested in replicating hold across a range of populations, settings/contexts, treatments and time. Extension allow you to test previous studies whilst trying to improve aspects of the original study, as well as test new, but related knowledge that may add greater understanding to the original study.
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