It is easy to get confused about the difference between literature reviews and essays because these two writing structures can be based on the same research. However, the main difference is on where the emphasis is placed.
The purpose of an essay is to use what is known about a subject to prove an argument or point of view. Not all of the knowledge of a topic may be used in an essay, but only what is relevant to the argument. In an essay, mentioning the people who discovered or developed the knowledge is generally only for referencing purposes.
On the other hand, a literature review is designed to be a critical analysis of all the knowledge that has been discovered about a subject. Its purpose is to examine all that others have already discovered about the subject and the researchers working on the subject are considered to be key.
At a sentence level, one way to emphasise a particular aspect of a subject is to place that aspect at the beginning of sentences and paragraphs.
In an essay, where the focus is on the knowledge itself, it is put to the front of sentences. For example:
Playing computer and video games have risen dramatically in popularity. It is estimated that three billion hours of gaming are played globally each week. The major reason for this is because players are able to tap into a high level of emotional satisfaction that is difficult to experience in everyday life (McGonigal, 2011).
However, in literature reviews what is considered to be more important are the authors and researchers who found or developed the information. Therefore they appear at the beginning of sentences.
Jane McGonigal (2011) estimates that three billion hours of gaming are played globally every week. Her research suggests that the major reason for this is because players are able to tap into a high level of emotional satisfaction that is difficult to experience in everyday life.
This is not to say that both kinds of sentences can be used in both types of writing. However, the overall trend for essays is to emphasise the information, whereas for literature reviews the trend is to emphasise the authors.