As you may have observed in the various examples given above, citation style is closely linked to tense. There are a few different ways of citing the studies you refer to in your literature review. It is tempting to simply refer to the authors directly in the sentence; indeed, many NNSE authors tend to use this approach almost exclusively. This results in a long series of sentences along the lines of “Argrave et al. (2013) showed that …., and Hillstead and Hampton (2012) found ….”. This style, when used exclusively, soon becomes monotonous, and many readers will find it difficult to focus on a literature review that is all written this way. Also, this style uses only simple past tense, which, as we have seen, should ideally only be used occasionally in the literature review.
We have also seen that, in addition to conveying different levels of confidence in the findings being reported, using different tenses also tends to involve using different ways of citing the literature. So while simple past tense usually involves mentioning the authors directly in the sentence, present perfect tense and simple present tense generally involve citing the authors parenthetically. Past perfect tense can use either type of citation.
Another factor to consider when choosing the tense to use is flow. In general, referring to the authors directly in the sentence breaks up the flow of the sentence and detracts from the impact of the statement. Consider the following two variations:
- Argrave and Johnson (2011) showed that oranges contain more Vitamin K than pears, but Black and Browne (2013) found that bananas contain even higher levels of Vitamin K.
- Although oranges have been shown contain more Vitamin K than pears (Argrave and Johnson 2011), bananas have been found to contain even higher levels of Vitamin K (Black and Browne 2013).
In the first variation, the reader must first focus on the names of the authors before they get to the finding. In fact, the reader might even feel that the author is more interested in who published these studies than in what the studies showed. In the second variation, however, the reader can easily skip over the parenthetical citations (and come back to them if they need to find the study), and it is clear that the points the author wants to make are about the Vitamin K levels of the fruit, not about who published which study.
Some journals, e.g. PLOS ONE, use the numeric citation style, in preference to the parenthetical style (see this paper for an example of how this is used). The numeric style is even less intrusive, and when preparing a paper for a journal that uses the numeric style, it is a good idea to take advantage of the opportunity to practice writing in a more flowing style, by referring directly to authors as seldom as possible in the text.