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Research Methods & Studies

Review Studies

The goals of a literature review are to summarize and analyze the current literature regarding a research question & to identify gaps in the current literature and make suggestions regarding future research that needs to be conducted on the topic.

"A literature review can broadly be described as a more or less systematic way of collecting and synthesizing previous research. An effective and well-conducted review as a research method creates a firm foundation for advancing knowledge and facilitating theory development. By integrating findings and perspectives from many empirical findings, a literature review can address research questions with a power that no single study has" (Snyder, 2019).

Further Reading:

"A scoping review is a type of knowledge synthesis that uses a systematic and iterative approach to identify and synthesize an existing or emerging body of literature on a given topic. While there are several reasons for conducting a scoping review, the main reasons are to map the extent, range, and nature of the literature, as well as to determine possible gaps in the literature on a topic" (Mak & Thomas, 2022).

"Scoping reviews are similar to systematic reviews but are conducted for different reasons. Scoping reviews tend to focus on the nature, volume, or characteristics of studies rather than on the synthesis of published data. Scoping reviews were developed in the early 2000s. Researchers saw the need for a review type that could be published that was less detailed than a systematic review but more detailed than a narrative (summary) review" (Nalen, 2022).

"Systematic reviews have the highest level of evidence of all research types. Scoping reviews do not contain the level of detail of systematic reviews. They may have a higher risk of bias due to higher heterogeneity. Thus, their level of evidence is considered only moderate. The benefit of scoping reviews is that they help map the literature on a specific topic. Additionally, they can inform future research and systematic reviews on that topic" (Nalen, 2022).

The Touro College of Osteopathic Medicine and College of Pharmacy Subject Guide has a lot of information relating to scoping reviews.

Further Reading:

The goals of a systematic review with meta-analysis is to eliminate bias & to analyze and synthesize the current literature, to address a specific research question, to develop a new best practice in its field of research. 

A systematic review collects all possible studies related to a given topic and design, and reviews and analyzes their results. A systematic review attempts to collate empirical evidence that fits pre-specified eligibility criteria to answer a specific research question.

The key characteristics of a systematic review are:

  • a clearly stated set of objectives with predefined eligibility criteria for studies an explicit, reproducible methodology
  • a systematic search that attempts to identify all studies that meet the eligibility criteria
  • an assessment of the validity of the findings of the included studies (e.g., through the assessment of risk of bias)
  • a systematic presentation and synthesis of the attributes and findings from the studies used

Systematic methods are used to minimize bias, thus providing more reliable findings from which conclusions can be drawn and decisions made than traditional review methods. Meta-analyses are often a subset of systematic review. Systematic reviews need not contain a meta-analysis there are times when it is not appropriate or possible; however, many systematic reviews contain meta-analyses.

The value and credibility of an SR depends on: importance of the question, the quality of the original studies, the efforts undertaken to minimize bias and the clinical applicability

A "good" systematic review also includes a comprehensive and critical discussion of the results, including strengths and limitations, such as assessment of bias, heterogeneity, and used definitions and categorizations. Ideally, the importance of the study is highlighted, considering clinical usefulness and the need for future research. Everything must be well described.

Meta-analysis is the use of statistical methods to summarize the results of independent studies.

Outcomes from a meta-analysis may include:

  • More precise estimate of the effect of treatment or risk factor for a disease than can be determined by an individual study
  • Rigorously conducted meta-analyses are useful tools in evidence-based medicine.
  • Typically, but not necessarily, the study is based on randomized, controlled clinical trials.

One important potential source of bias in meta-analysis is the loss of trials and subjects.

Meta-analysis is important because research questions are typically studied more than once, often by different research teams in different locations. In many instances, the results of these multiple small studies of an issue are diverse and conflicting, which makes the clinical decision-making difficult. Therefore, meta-analysis, a statistical procedure that integrates the results of several independent studies.

The differences and similarities between systematic reviews and meta-analysis:

Both:

  • Systematic reviews and meta-analyses present results by combining and analyzing data from different studies conducted on similar research topics.

Bias: The greatest potential for bias in both Meta-Analysis & Systematic Reviews are flawed original studies that were selected for analysis and synthesizing.

Difference:

  • A systematic review is a detailed, systematic, reproducible and transparent means of gathering, appraising and synthesizing evidence to answer a well-defined question.
  • A meta-analysis is a statistical procedure for combining numerical data from multiple separate studies. A meta-analysis should only ever be conducted in the context of a systematic review. Meta-analyses are a subset of systematic review.

A systematic review attempts to gather all available empirical research by using clearly defined, systematic methods to obtain answers to a specific question. A meta-analysis is the statistical process of analyzing and combining results from several similar studies.