LITERATURE REVIEW

Prof. Jimmy Volmink
Primary Health Care Directorate
UCT Faculty of Health Sciences

Note: You may see the Power Point presentation used at the lecture.

What is a literature review?

A literature review is:

• an account of what is written on a particular subject by scholars and researchers.

• Its purpose is to convey current knowledge and ideas as well as their strength and weaknesses.
• It may be part of essay, a research report or thesis, or a stand alone exercise.

Annotated bibliography vs. literature review

An annotated bibliography is a list of sources each accompanied by a brief note (annotation) discussing one or more aspects, such as content, usefulness, or quality.

On the other hand, a literature review is a piece of discursive writing that presents themes and concepts, and/or integrates ideas and concepts.

Objectives of a literature review:

The objectives of a literature review may be listed as follows:

1. Address a research question or thesis.
2. Critically appraise research for validity.
3. Synthesize and summarise current knowledge.
4. Identify controversies in literature.
5. Formulate questions for future research.

The so-called "information explosion" has vastly increased the load of research workers who wish to keep up with their respective fields. Consider the availability of the following:

• journals;
• textbooks;
• unpublished literature;
• World Wide Web;

One fundamental purpose of literature reviews is to reduce the load!

What do we want from a literature review?

Ideally, a literature review should be:

• a readable summary of ALL the evidence;
• unbiased;transparent;
• up-to-date.

Note for GRD: Discuss slides 9-11 after contacting Prof Volmink

The traditional literature review:

The traditional literature reviews can be said to be characterised by:

• Qualitative, narrative summaries of evidence on a given topic usually written by an expert in the field.
• They typically involve informal and subjective methods to collect and interpret the information.

Problems with traditional reviews:

1. Bias in selection of included studies:

• Personal (“file drawer”) bias.

• Publication bias: studies with statistically significant results are:

  • more likely to be published
  • more likely to be published in English
  • more likely to be published in journals with high citation impact factors 

    Easterbrooke et al, Lancet 1991

2. Indexing bias:

RCT stands for Randomised Control Trials. Note from GRD: What does the diagram purport to show?

3. Variable quality of published studies:

At the Fourth Congress on Peer Review in Biomedical Publications, it was stated that:

• “Medical journals are full of serious methodological errors “;
• “Journal editors are giving no time, energy and thought to their craft”;
• “Studies are published that reach false conclusions”

  BMJ, Sept. 2001:323

4. Effect of Study Design:

Consider the following (Ann Intern Med. 2003;139:56-70.):

PURPOSE: To assess the evidence of the effectiveness of vitamin supplementation, specifically vitamins A, C, and E; beta-carotene; folic acid; antioxidant combinations; and multivitamin supplements, in preventing cardiovascular disease.

STUDY SELECTION: The researchers selected English-language reports of randomized trials and cohort studies that assessed vitamin supplementation in western populations and reported incidence of or death from cardiovascular events.

CONCLUSIONS: Some good-quality cohort studies have reported an association between the use of vitamin supplements and lower risk for cardiovascular disease. Randomized, controlled trials of specific supplements, however, have failed to demonstrate a consistent or significant effect of any single vitamin or combination of vitamins on incidence of or death from cardiovascular disease.

5. Effect of Study Size:

JRA Mitchell (BMJ 1981;282:1565-70) states that:

“ … we still have no clear evidence that beta-blockers improve long-term survival after infarction despite almost 20 years of clinical trials.”

If we are to do better than what is provided by Traditional Reviews, we should bear in mind the "The Science of Research Synthesis". Lord Rayleigh wrote in 1884:

If science consisted of nothing but the laborious accumulation of facts, it would soon come to a standstill...…
Two processes are at work side by side, the reception of new material and the digestion and assimilation of the old; and both are essential…”

The systematic review:

How is it different?

A systematic review may be defined as one in which bias has been reduced by the:

• systematic identification,
• appraisal,
• synthesis
• statistical aggregation (if relevant)

of all relevant studies on a specific topic according to a predetermined and explicit method. (See Moher et al. Lancet; 354: 1896-900).