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 Table of Contents  
Year : 2014  |  Volume : 7  |  Issue : 1  |  Page : 1-4

Evidence-based medicine

Parasitology Department, Faculty of Medicine, Cairo University, Cairo, Egypt

Date of Submission14-Feb-2014
Date of Acceptance01-Jun-2014
Date of Web Publication25-Sep-2014

Correspondence Address:
Amany A Abd El-Aal
Parasitology Department, Faculty of Medicine, Cairo University, Cairo
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1687-7942.139684

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How to cite this article:
Abd El-Aal AA. Evidence-based medicine. Parasitol United J 2014;7:1-4

How to cite this URL:
Abd El-Aal AA. Evidence-based medicine. Parasitol United J [serial online] 2014 [cited 2023 Dec 3];7:1-4. Available from: http://www.new.puj.eg.net/text.asp?2014/7/1/1/139684

  What is evidence-based medicine Top

Evidence-based medicine (EBM) has been defined as 'the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients [1] . A more simple description is 'integrating the best research evidence with clinical expertise and patient values to achieve the best possible patient management'. Consequently, improvement of the quality of a patient's life is considered the chief goal of medicine. This description emphasizes the three important parts of evidence-based medical practice: the patient, the evidence, and the careful application of generalized evidence to the individual patient. Accordingly, it is termed as EBM trait, in which evidence from best research is incorporated not only with clinical expertise, but also with patients' values and expectations.

Individual clinical expertise signifies the proficiency and judgment that individual professions acquire through experience and practice. Such proficiency reflects in more effective and efficient diagnosis, and in more considerate use of patients' rights and preferences in making clinical decisions [2] .

The best clinical evidence usually targets the clinically relevant research studies (often from the basic sciences of medicine), the accuracy of diagnostic techniques, the strength of prognostic markers, and the efficacy and safety of therapeutic and preventive regimens. As a result, recent evidence is expected to invalidate previously accepted managements and replace them with new ones that are more powerful, more accurate, more efficient, and safer [3] .

  What are the appropriate clinical approaches? Top

When facing a health problem, usually the question will be: how do I decide what to do? The decision can be guided by a number of different approaches. Some decisions are guided by dogma, or a-priori set of beliefs - for example, natural remedy is the best. Some decisions are guided by tradition relying on the collective wisdom of the ages - for example, we have always done it that way. Other decisions are guided by convention relying on the collective wisdom of colleagues - for example, everyone else does it that way. However, the evidence-based approach provides decisions based on critical evaluation and reflection - for example, the evidence supports a certain concept. Before any medical decisions, EBM encourages searching for and application of the current best evidence. Therefore, an appreciation of how to evaluate or grade evidence is crucial to the application of best evidence in practice [4] . Hence, searching is a necessity and not a luxury in the medical field.

Undoubtedly in the medical history, innovational and evolutional steps have been reflected on human health, minimizing mortality and morbidity, thus improving the quality of life - for example, before discovery of antibiotics, millions died from septicemia, especially during war. The key word in this dilemma is education, which in general raises the standard of societies. Therefore, continuous medical education is necessary to improve the standard of professions in the medical field [5] .

  Why use an evidence-based approach? Top

The main objectives of evidence-based approach are increasing the capability to get current information, ability to conduct a direct review of the evidence, and development of an interactive form of continuous medical education. Good-quality education teaches us to become both producers of knowledge (adding scientific knowledge) and consumers of what other people claim to know (learning from scientific knowledge).

  How can we obtain the best available evidence? Top

In practice there are certain steps of EBM that should be followed [3] . These were summarized into five steps, generally categorized as follows:

  1. Formulation of clinical questions so that they can be answered.
  2. Searching for the best external evidence.
  3. Clinically appraise that evidence for its validity and importance.
  4. Application of results in practice.
  5. Evaluation of performance.

To simplify such process, the five 'A's' categorization is as follows: Ask the right question. Acquire the evidence. Appraise critically the evidence (i.e. find out how good it is). Apply the evidence by integrating results with clinical expertise and patient values. Finally, Assess its impact and evaluate the effectiveness.

  How do we formulate the clinical question? Top

To formulate the right question, a precise method that includes specific points should be verified. The first point is related to the medical Problem or/and the target Population; the second point is linked to the applied Intervention in the study in Comparison with other interventions used in other studies; the target of the third point is the expected Outcome; and the fourth point is the Study design that must be clarified. In other words, the question should be framed in the context of the PICOS format questions. This stands for Population receiving an Intervention (diagnostic test or treatment) as Compared with other tests/treatments associated with the Outcome (disease or improvement) [6] .

Medical outcomes

These are vital tasks in the medical field. To decide what to do in practice, we need to know as well what kind of outcomes to seek. Accordingly, 'Medical Outcomes' can be broadly grouped into three categories. Some outcomes (e.g. immunoglobulins or eosinophil levels) are considered as markers of disease. These markers are measured because they may help as prognostic tests, but they have no direct impact on patient's recovery. Others that measure actual stage or extent of disease are considered as disease-oriented outcomes (e.g. the extent of Leishmania spp. ulcers or the inflammatory degree of the disease). These may have a more direct influence on a patient's quality of life or degree of suffering, but yet do not evaluate the long-term quality of life. The most important 'outcomes' for guiding medical decisions are those that affect the quality of patients' lives (patient-oriented outcomes), such as suffering, longevity, and other considerations that directly affect the quality of life. In short, patient-oriented outcomes have primarily to do with long-term morbidity or mortality [7] .

Disease-oriented and patient-oriented outcomes

According to the measured outcomes, clinical questions generally fall into two types: Background questions that mean 'What is it?' are related to general information of a condition or disease 'Disease-Oriented Evidence Matter' or DOEM questions. Foreground questions that mean 'What can I do for this patient?' are related to the degree of improvement, such as morbidity or mortality. These are 'Patient-Oriented Evidence Matter' or POEM questions [8] . To explore the DOEM issue, the following is an example of a question targeting the disease: should I screen pregnant women for toxoplasmosis? While the following is an example of a better question targeting the patient: would a screening test for nonimmune pregnant women reduce morbidity? This is a POEM question. Another example for POEM is a PICO format question: in a 20-year-old worker with cutaneous leishmaniasis (patient), will topical pentavalent (intervention) compared with no treatment (comparison) lead to quicker symptom relief (outcome)?

  How do we acquire the evidence? Top

Resources of evidence can range from unsystematic clinical observations of individual clinicians to systematic reviews of multiple randomized controlled trials (RCTs). The various forms of evidence may offer clinical recommendations that bring about good outcomes for patients, but it is clear that some forms of evidence are more reliable than others in giving guidance to clinicians and their patients. Therefore, a hierarchy of the strength of evidence has been used to direct decision making. The assumption is that the stronger the evidence, the more likely the proposed treatment or diagnostic test will lead to the predicted result.

  What is the hierarchy of strength of evidence? Top

Evidence hierarchies reflect the relative authority of various types of biomedical research. Although there is no single, universally accepted hierarchy of evidence, there is a broad agreement on the relative strength of the principal types of research, or epidemiological studies. RCTs rank above observational studies, whereas expert opinion and subjective experience are ranked at the bottom [9] . Some evidence hierarchies place systematic review and meta-analysis above RCTs, as these often combine data from multiple RCTs, and possibly from other study types as well. The use of evidence hierarchies has been criticized as allowing RCTs too much authority. However, not all research questions can be answered through RCTs, either because of practical or ethical issues. Moreover, even when evidence is available from high-quality RCTs, evidence from other study types may still be relevant [10] . The relative weight carried by the different types of primary study (the hierarchy of evidence) puts them in the following order:

  1. Systematic reviews and meta-analyses.
  2. RCTs with definitive results (confidence intervals that do not overlap the threshold for clinically significant effect).
  3. RCTs with nondefinitive results (a point estimate that suggests a clinically significant effect but with confidence intervals overlapping the threshold for this effect).
  4. Cohort studies.
  5. Case - control studies.
  6. Cross - sectional surveys.
  7. Case reports.

  What are the uppermost types of biomedical research? Top

Systematic reviews

A systematic review is a high-level overview of primary research studies on a particular research question. This question tries to identify, select, synthesize, and appraise all high-quality research evidence relevant to that question. Systematic reviews seek to assemble all evidence that fits prespecified eligibility criteria to address the research question. Systematic reviews as well aim to minimize bias by using explicit, systematic methods [4] .


A meta-analysis refers to methods that focus on comparing and combining results from different studies, to identify patterns among study results, sources of disagreement among these results, or other interesting relationships. The general aim of a meta-analysis is to more powerfully estimate the true effect size in numerous studies as opposed to a less precise effect size derived in a single study under a given single set of assumptions and conditions. A meta-analysis therefore gives a thorough summary of several studies that have been conducted on the same topic, and provides the reader with extensive information on whether an effect exists and what size that effect has. Moreover, meta-analyses are often, but not always, important components of a systematic review procedure. It forms part of a framework called estimation statistics, which relies on effect sizes, confidence intervals, and accuracy planning to guide data analysis, and is an alternative to null hypothesis significance testing [11] .

Cohort study

A form of longitudinal study for analysis of risk factors and follows a group of people who do not have the disease, and uses correlations to determine the absolute risk of subject contraction. A cohort is a group of people who share a common characteristic or experience within a defined period.

Case-control study

A type of epidemiological observational study. An observational study is a study in which subjects are not randomized to the exposed or unexposed groups, rather the subjects are observed to determine both their exposure and their outcome status, and thus the exposure status is not determined by the researcher.

Cross-sectional study

A type of observational study that involves data collection from a population, or a representative subset, at one specific point in time.

Case report

A detailed report of the symptoms, signs, diagnosis, treatment, and follow-up of an individual patient. Case reports may contain a demographic profile of the patient, but usually describe an unusual or novel occurrence [10] .

  How do we appraise the evidence? Top

The concept of EBM requires an understanding of critical appraisal and the basic epidemiologic principles of study design, point estimates, relative risk, odds ratios, confidence intervals, bias, and confounding. Some questions should be answered while 'Appraising the Evidence'.

  1. Is the study valid?
  2. What are the results?
  3. What is the outcome and how was it measured?
  4. What is the magnitude of the effect?
  5. Are the results statistically significant?
  6. Do the results apply to my patient?
  7. Does my patient resemble those in the study?
  8. Were all outcomes relevant to my patient's evaluation?
  9. Are there other factors (e.g. cost, availability) that limit applicability to my patient?

By using this information, we can categorize evidence, assess causality, and make evidence-based recommendations. EBM allows analysis of complicated data so that we can make the best possible decisions for the population or scientific problem we serve [2] .

  What are the sources of evidence? Top

For several decades, the usual way of acquiring information has been the review of traditional textbooks and ongoing medical journals. Unfortunately, it has been shown that knowledge related to management of patients in textbooks goes out of date quickly. Besides, owing to the huge number and variety of journals, it is challenging even for the most hard-working medical professions to stay up to date. With the development of modern technology that allows easy and rapid access to MEDLINE and other full-text rapid internet access sites, an increasing number of busy medical professions have been able to obtain current evidence [7] . Some important sources are as follows:

PubMed: Sixteen million peer-reviewed biomedical articles indexed (PubMed limits can be used to search on particular populations, study types, etc.).

Cochrane library: The Cochrane Collaboration is one of the chief sources of evidence that prepares, maintains, and promotes systematic reviews to inform healthcare decisions: Cochrane reviews ˜3000 clinical systematic reviews (gold standard database).

Clinical evidence: Approximately 2500 systematic reviews of treatment classified by likelihood of benefit.

InfoPOEMS: Approximately 3000 regularly updated entries, Patient-Oriented Evidence that Matters (POEM), 100+ journals monitored.

UpToDate: A total of 70 000 pages, evidence-based clinical information resource, ˜3000 authors, 350+ journals monitored, peer reviewed.

TRIP+ metasearch of 55 sites of evidence-based information [7] .

Limitations of evidence-based medicine

Despite its ancient origins, EBM remains a relatively young discipline whose positive impacts are just beginning to be validated, and it will continue to develop. One of the biggest concerns among busy medical professions is the large amount of time required to develop and maintain an EBM in practice. Adding the time and cost to obtain a range of new skills, such as critically appraising the literature and grading up to date evidence, can seem overwhelming.

Improving the number and quality of available research trials and teaching the principles of EBM in undergraduate and graduate medical training will be important for establishing its widespread use. These training programs, and their evaluation, will provide further information and understanding about EBM [10] .

  Acknowledgements Top

  References Top

Sackett DL, Rosenberg WM, Gray JA, Haynes RB, Richardson WS. Evidence based medicine: what it is and what it isn't. BMJ 1996; 312: 71-72.  Back to cited text no. 1
Williams JK. Understanding evidence-based medicine: a primer. Am J Obstet Gynecol 2001; 185:275-278.  Back to cited text no. 2
Montori VM, Guyatt GH. Progress in evidence-based medicine. JAMA 2008; 300:1814-1816.  Back to cited text no. 3
Druss B. Evidence based medicine: does it make a difference?: use wisely. BMJ 2005; 330:92.  Back to cited text no. 4
Oxman AD, Glasziou P, Williams JWJr. What should clinicians do when faced with conflicting recommendations? BMJ 2008; 337:a2530.  Back to cited text no. 5
Huang X, Lin J, Demner-Fushman D. Evaluation of PICO as a knowledge representation for clinical questions. AMIA Annu Symp Proc 2006; 2006:359-363.  Back to cited text no. 6
Ebell MH, Siwek J, Weiss BD, Woolf SH, Susman J, Ewigman B, Bowman M. Strength of recommendation taxonomy (SORT): a patient-centered approach to grading evidence in the medical literature. Am Fam Physician 2004; 69:548-556.  Back to cited text no. 7
Slawson DC, Shaughnessy AF, Ebell MH, Barry HC. Mastering medical information and the role of POEMs - Patient-Oriented Evidence that Matters. J Fam Pract 1997; 45:195-196.  Back to cited text no. 8
Guyatt GH, Sackett DL, Sinclair JC, Hayward R, Cook DJ, Cook RJ. Users' guides to the medical literature. IX. A method for grading health care recommendations. JAMA 1995; 274:1800-1804.  Back to cited text no. 9
Burns PB, Rohrich RJ, Chung KC. The levels of evidence and their roles in evidence based medicine. Plast Reconstr Surg 2011; 128:305-310.  Back to cited text no. 10
Cates CJ, Cates MJ. Regular treatment with salmeterol for chronic asthma: serious adverse events. Cochrane Database Syst Rev 2008:CD006363.  Back to cited text no. 11


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  In this article
What is evidence...
What are the app...
Why use an evide...
How can we obtai...
How do we formul...
How do we acquir...
What is the hier...
What are the upp...
How do we apprai...
What are the sou...

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