The foundation of scientific research tasks/projects is to conduct research and establish a connection between the study’s objective and the existing body of knowledge, regardless of the field. To implement the methodological scheme, the literature review section should be regarded as a seniority among all academics ^[1]. In a similar route, the collection of information is seen as a crucial element for any area to be deemed “scientific” and “credible” ^[2]. To be more accurate, formulating impactful literature reviews is of great significance in producing and accelerating knowledge. ^[3]. A literature review is at the heart of the scientific projects and engrosses a significant corner of academic activities, in other words, it is considered the pillar of all social, business and engineering research. In the current global research, the frontiers of knowledge bases are extending month by month. Thus, it is becoming more important to enhance the published body of information. Fundamental to this concept is the notion that ground-breaking ideas build upon previously published research ^[4]. In essence, a literature evaluation demonstrates the need or need for doing fresh investigations ^[5][6]. As one of the most fundamental properties of research work, Creswell ^[5] expounded the definition in a special frame:

“The literature review in the context of a research study fulfills numerous objectives: (a) It shares the findings of other studies which are relevant to the study being reported with readers. (b) It links a study and ongoing stretches in the literature and extends prior studies. (c) It sets up a pertinent framework to justify the significance of the study (pp. 20–21).

Many researchers suppose that their art of research report is accepted with no resistance from evaluators. They are unsuccessful in perceiving the underlying significance of the literature review. The detailed view of reviewers attracts the literature review which is considered an “Achilles’ heel” of many researchers ^[7]. Looking at this issue through a scientific lens, researchers of some ilk are unaware of what fleshes out research, and likely they still presume that a literature review is not sheerly a formality ^[8].

Now, all the fundamentals necessary for a complete comprehension of the definition, aims, and relevance of a literature review have been emphasized. A literature review is one of the disciplines of research. Each study plan should adhere to a blueprint strategy to be carried out. Initially, a study contributes a fresh horizon of thought to an existing theory or empirical body of research by validating the theory in new contexts or elaborating it. To go ahead, elaboration or validation calls for a stretch of evidence that is employed to generate new hypotheses. They also play a part in explaining why and how the new lines of implications are relevant. One step beyond the basic concerns, the focus changes to practical issues. Researchers should centralize their integral aim in ascertaining how the new findings would untie the practical gaps ^[9].

It has been established that literature reviews aggregate data from much research, suggesting that when numerous results go in the same direction, more confidence in the reliability of conclusions may be accumulated ^[10]. In the second view, literature reviews open up new chambers for researchers to tap into broad questions. Put simply, they draw on research that exerted a variety of research methods and measurements ^[11]. In this sense, the literature review “foreshadows the researchers’ study” ^[12]. In summarizing the significance of literature review, ^[13] noted that literature reviews operate as a stimulant, motivating researchers to educate themselves on as large a body of relevant information as possible. Furthermore, they are apropos indicators to readers that the author(s) had a robust perception of the research topic. It has been maintained that through scrutinizing and reviewing the literature review on the previous literature, all shortcomings and foibles of prior studies will be lightened ^[14][15]. Therefore, they would enact as a lantern in creating and enriching the existing study context for conducting further research and even facilitating argument formulation.

One step beyond the nature and significance of literature reviews is the matter of centralization. Literature reviews could embrace several various focuses, which vary from one study to another. The leading focus deals with researchers’ conception of general research questions ^[16]. About the research questions, underlying concepts of research questions should cover all the domains of prior literature about the research topic, even if it does not straightly conform. In the second view, literature reviews enjoy high potential in educating readers about whether studies contribute to the accumulated knowledge or not. Hence, literature reviews help in fulfilling the integral aim through spotlighting on delineating themes and notions and stretches of relevant issues to the topic.

2. Types of Literature Review

Numerous sorts of literature reviews have developed over time. Briefly, the following are some step-by-step tips for conducting a literature review:

• Narrowing the subject and picking papers accordingly
• Literature search
• Reading and reviewing the selected articles thoroughly
• Organizing the chosen papers by identifying patterns and developing subthemes
• Creating a thesis or mission statement
• Developing the paper
• Reviewing the work

The selection of a certain kind is determined by your study methodology and design. In the following subsections, several classifications of literature reviews, including their merits and drawbacks and scope of application, are examined.

2.1. Narrative Literature Review

As a social process including aggregate and iterative steps, this type of literature review has its basis in process theory. According to the purpose and application scope, narrative reviews focus on developing theories as their main goal ^[17][18], and typically they have appositeness in various fields namely humanities, management research, and social sciences ^[19][20]. A narrative review is defined as a thorough narrative synthesis of prior published information. Looking at the definition from a different perspective, narrative reviews are qualitative summaries of the relevant literature (whether statistics were used or not). They have a lot of potential for bringing together studies that looked at different research questions and approaches/methodologies ^[4]. The process of conducting this type is considered non-structured, multilayered, and calls for sundry cumulative written outcomes which occur in a social context ^[18]. In addition to the extensive coverage of benefits and application in narrative reviews, some drawbacks have been found, hence researchers are recommended to be cautious in this regard. The greatest weakness has been attributed to the issue of “bias” in drawing the conclusions (Webster and Watson ^[21]). Bias may be rooted in the seedling stage of processing a review. There is less consensus about how experts have been selected. In the second view, the completeness and wide coverage of narrative reviews in different fields have been corroborated. However, this type does not ineluctably follow regulations in searching for evidence ^[22]. Concerning evidence, Schlesselman and Collins ^[23] asserted that some complicated and evolving background knowledge and notions need a wide range of situational choices about the inclusion of evidence and thus call for more flexible narrative reviews. Thirdly, in typical narrative reviews, there are no traces of how conclusions and decisions were made about the pertinence of studies and the validity of the included studies. Casting much light, Schlesselman and Collins ^[23] maintained that the findings of one piece of research should meet the referees’ sense of legitimacy. However, readers might not make any judgments on the authors’ choices. 

2.2. Systematic Literature Review

Contrary to narrative reviews, systematic literature reviews adopt a more robust approach to reviewing the literature. The rigorousness of such reviews can be attributed to the fact that systematic reviews mostly have their centralization in answering structured and particular research questions ^[24]. Generally speaking, systematic reviews have their applicability scope in domains namely healthcare literature, traditional social science, and business management literature reviews ^[25][26]. At the heart of all fields, the string of systematic review utilization has been interwoven with healthcare movements in the late 1970s and early 1980s. They have emerged in unwinding the gaps in finding an “evidence-based medicine movement” by using and organizing the accessible knowledge on the efficaciousness of healthcare remedies into dependable formats ^[24]. Systematic reviews were defined as “a method of making conclusions from a bundle of information and is considered as a means of sharing the answers to research questions about what works and what does not” ^[24]. In line with the definition, Jesson, Matheson ^[25] have demonstrated that this type of review concentrates on accelerating the body of research knowledge and can be both qualitative and quantitative. Compared to narrative reviews, systematic reviews encompass a more goal-based appraisal of evidence. Thus, since systematic reviews adopt a methodological approach, they are less prone to bias and error. As in narrative reviews, the type of exerted methods in singling out the pertinent data are not pellucid enough. Therefore, the selection of the study can be arbitrary (can be affected by reviewers’ bias) ^[27][28]. One line of strength in systematic reviews is associated with the level of precise and reliable appraisals, meaning that they are critically appraised, the strength of evidence is assessed, and quantitative synthesis of data is carried out ^[29]. In the third view, a reproducible process of systematic research synthesis lends a hand in untying any incertitude between the original study, traditional literature reviews, and experts’ credence ^[30]. Looking at the benefits from a research-based view, it has been highlighted that systematic reviews assist in abating the time interval between research discovery and implementation and enhance the generalizability of the results.

2.3. Meta-Analysis Literature Review

In retrospection to the aforementioned types of reviews, it has been stated that compared to narrative reviews, meta-analysis literature reviews are newer and apply a quantitative method of integrating the results of prior studies ^[31]. There is a disagreement between users of the two methods, some scholars who tend to inject this approach into their studies opine that narrative approaches and reviews have become obsolete. However, both have specialized a promising place in science ^[32]. Meta-analysis is a preferred type of literature review in combining the results of a multitude of studies that have adopted comparable methods in addressing a similar research question. Put the definition in another way, meta-analysis literature reviews include taking results from the selected literature and analyzing the results under the shade of standardized statistical techniques ^[31][33]. The arrays of applicability in meta-analytic reviews are extended into realms of economic studies such as cost-effective analyses, biomedical, and medical research (establishing the association between the amount of exposure and disease) ^[34]. Further, the obtained results from meta-analyses can be applied in verifying the acceptable sample size of a future trial ^[35]. Interestingly, what makes a borderline between systematic and narrative reviews with meta-analysis literature reviews is the potentiality of drawing conclusions and finding patterns and relationships between the findings ^[36]. It has been discussed that by pooling significant findings with non-significant findings from the related studies, meta-analysis reviews enjoy enhanced potential in appraising more accurate estimates of a phenomenon’s effects ^[37][38][39]. As one of the most powerful research methods, meta-analyses open up new chambers for researchers to draw apropos inferences through reliance on existing controversies ^[40].

2.4. Umbrella Literature Review

Umbrella reviews are typically characterized as reviews of prior published meta-analyses and systematic reviews. They are one of the highest methods in representing evidence synthesis ^[41]. Taking the great prevalence and contribution of umbrella reviews in advancing the body of knowledge at this time interval, they are becoming highly injected with their vitality in the biomedical literature reviews, medical research, psychology, and genetics ^[42][43]. Addressing the applicability of umbrella reviews, it has been demonstrated that meta-analyses and systematic reviews generally have their major concentration on synthesizing the previous results and detecting the biases. However, as the number of reviews in these types increases, researchers find themselves in an overwhelming world. To find a remedy addressing this problem, umbrella reviews have emerged to fill out the existing knowledge gap ^[42]. Scholars who have conducted reviews in the channel of umbrella reviews opined that in most cases they are required to rely on the available information of systematic and meta-analyses, though, caution should be made in conceding the potential limitations ^[44]. Secondly, in selecting factors with a sufficient string of evidence and corroborating the data, umbrella reviews adopted systematic and meta-analyses literature reviews ^[45]. In line with thoroughly presenting the evidence in the scope of umbrella reviews, researchers should sufficiently take the limitations into account. From this respect, one of the most critical pitfalls is the limited scope of the report, meaning that umbrella reviews could just provide a report on what researchers have interrogated and published ^[46]. The second drawback is attributed to the necessity of knowledge novelty. In this regard, umbrella reviews can encompass all the studies even beyond what has been included in the range of published reviews. Such a comprehensive inclusion calls for fresher literature research, and accordingly, it requires more time and works devotion that becomes unfeasible ^[43].

2.5. Descriptive Literature Review

A descriptive literature review is the summarization of individual research and mostly provides researchers with nuts and bolts of two important sections of methodology and results of the cited research ^[47]. The integral aim of this type of review is to present an explicable pattern of the existing literature reviews, these patterns generally provide quantified reports in the form of frequency analysis such as research methodology and research outcomes ^[47]. The process of conducting a descriptive review is systematic and includes searching, filtering, categorizing, codifying, and analyzing ^[48]. Magnifying the systematicity of the procedure, scholars delineated that at the seedling stage reviewers need to collect as many research papers as possible. In this line, they should carry out thorough research on the related literature ^[37][49][50]. Following the data collection, reviewers scrutinize each paper individually to reflect the frequencies of the topic, researchers, and the employed methods and to detect the patterns and trends among the surveyed research papers ^[51]. The overall resulting patterns are the manifestos of a research area. Extending the significance line to applicability scope, descriptive reviews have their utilization traces in educational settings, engineering research studies, and psychology. Highlighting the benefits of descriptive reviews, it has asserted that this type provides an in-depth picture of the intended fields of interest. Second, researchers can utilize the results of descriptive literature reviews to generate new research hypotheses and questions from cause-and-effect relationships ^[52].

2.6. Scoping Literature Review

Scoping literature reviews are generally used to present a primary indication of the size and nature of the literature in specific fields of interest ^[53]. The integral objective of scoping reviews is to inspect the range and essence of research activities and particularly, verify the valuation of conducting systematic reviews and determining the research niches ^[54]. To better understand the nature of scoping reviews, it has been defined as exploratory research which systematically outlines the available literature on a topic, searches for key concepts, theories, and the origin of evidence, and more importantly addresses the existing gaps in research ^[55]. Scoping literature reviews have become increasingly trendy in healthcare research domains. Interestingly, from 2012 until the current time, the number of conducted scoping reviews has been accelerated, it has been argued that such an upsurging advancement in scoping review is attributed to its high potential in assisting research agendas and policymakers ^[53].

2.7. Critical Literature Review

Due to the extensive horizons of connection to other works and researchers across different fields of studies, critical literature reviews have allocated a great deal of research value in the larger academic milieu ^[56]. In the literature review domain, critical reviews have targeted the appraisal of information and synthesis particularly by magnifying observations and drawing wind-ups ^[57]. In a general view, critical reviews are objective and comprehensive rundowns and critical analyses of the related literature with all foibles, controversies, and inconsonances on the matter being examined ^[58]. The applicability scope of reviews of this type includes ecological studies ^[59], clinical and particularly nursing ^[59][60]. Delving into the deep layers, critical reviews collect information about sundry sources and encompass all pertinent to the topic being studied namely historical records, books, government reports, journal articles, theses, and dissertations.

3. Common Errors in Conducting Literature Review

Since minority individuals are provided with explicit instruction on how to carry out a literature review, many attempted to learn it mostly through the trial-and-error process. The first and utmost error is associated with the state/quality of purpose, it is of great significance to know the aim of the literature review. Many authors mistakenly suppose that the major objective of the literature review is to summarize the previous studies on a specific topic. However, a summarized capsule of past findings does not merely formulate a unified whole. Ideally, a clear goal enacts a beneficial role in advancing the field’s theoretical perception and could lead to introducing new theories that connect a sundry of findings. It has been demonstrated that a mature topic would broach a novel enhanced understanding of a theory by testing it against the previously published works ^[57]. The second mistake is associated with the mechanical components. An ambiguous introduction and weak organization would deviate readers to find the precise findings. Some authors do not follow a logical plan in formulating their literature review, that is they provide a brief introduction about the significance and niches of the study. Following that, the research findings are discussed, and once all of the content is covered, they initiate presenting their theoretical perspectives from the resulting themes and conclusions ^[61]. The next common mistake is the lack of providing adequate information about the intended literature review. Presenting superfluous or too few details about some works put constraints on the overall understanding. Generally, a literature review has centralized its integral aim in summing up particular research methods and findings from the studies it cited. Any pieces of empirical study contribute to the authentic data and have its reliance on how well they could justify the findings. Illustrating the essence of evidence is of great importance ^[62].

4. Thumb Rules in Writing Literature Review

Regardless of what type of literature review is going to be conducted, if researchers intend to formulate a thorough literature review, they need to strive to be as comprehensive as possible. At the seedling stages, the most integral and delicate rule to highlight is to ring in the need and goal of writing the literature review. The need for conducting a literature review can be grounded on an out-of-date notion of a topic, recent development and variegation of the literature, particularly on a novel and emerging topic ^[63]. In detail, debating can be carried out on a topic that has been already demystified by entrant theories or operationalized in various ways and it could be the extended version of the literature. It should be pinpointed that researchers can present the literature review as a composition of more than one theory. Researchers might demonstrate their success with the data and, by extension, the body of ideas, in this respect, by offering tenable explanations based on evidence. As the literature on a new subject of interest initiates to accumulate and becomes the pillar of the literature body, researchers can assist in the literature review to tie each single study string together and analyze them to detect different viewpoints and insights. Moreover, shortcomings, imprecision, and any further problems. From this respect, selecting an apropos topic would make the study review distinct from the pertinent topics, support the concentration of the study, and set out boundaries to lay out the literature. Establishing boundaries for the topic would become the crux in developing the criteria to keep or discard the literature retrieved in the scope of the literature search later in the study ^[10]. One step above the topic of literature is the discussion of methods in the conducted literature. For all types of reviews and particularly for new topics in which the confirmed model/framework has not been thoroughly built up, the discussion is required to involve the means exerted to certify the validity or dependability of the resulting themes ^[63]. Similar to all research reports, the employed methods should be delineated in an adequate brass track so that readers could easily verify whether the literature on the topic has been injected into the study and so that researchers can replicate the study based on the research method. Once the methods of literature are elucidated, it is the repined time to critically analyze each study in the literature ^[64]. Through reviewing the multitude of articles, researchers have gained a broad perception of the literature quality, and therefore the basis for critical analysis is prepared. Critical analysis helps in determining the advantage, disadvantage, and inconsistencies in the literature and evaluates how well the literature manifests the topic ^[4]. Using the general arrangement and composition of literature as a guide, scholars are encouraged to create a harmonic flow of concepts and ideas so that readers can discern the entire (e.g., conceptual, methodological, and temporal structures). In some types of literature such as mapping and umbrella reviews, the organization of literature includes diagrams and visual representations. In this regard, the systematic structure and order of representations would highly enhance readers’ understanding of the addressed matter on hand. The literature evaluation should include traces of future subjects in the targeted discipline, as well as the aforementioned niceties. The traces include factors that have shaped the future of the topic, dissertate the pending advancements in the field of interest, and further assess the probable arrays for future trends ^[21][63].