Appendix A: Glossary of Evidence-Based Terms

Absolute Risk Difference: The arithmetic difference between the rates of events in the experimental group and the control group.

Absolute Risk Reduction (ARR): The difference in the event rate between the control group (CER) and the experimental group (EER): ARR = CER - EER. For example, in a study investigating the use of a new treatment in remineralizing enamel surfaces, the ARR would be the absolute difference between the proportion of decalcified enamel surfaces in the control group and those in the experimental group.

Case Control Studies: Studies in which patients who already have a certain condition are compared with people who do not. Case control studies are less reliable than either randomized controlled trials or cohort studies. Just because there is a statistical relationship between two conditions does not mean that one condition actually caused the other.

Case Series and Case Reports: Consists either of collections of reports on the treatment of individual patients or reports on a single patient. Case series and case reports, since they use no control group with which to compare outcomes, have no statistical validity.

Cochrane Collaboration: Cochrane Collaboration is an international endeavor in which people from many different countries systematically find, appraise, and review available evidence from randomized controlled trials (RCTs). The Cochrane Collaboration's aims are to develop and maintain systematic, up-to-date reviews of RCTs of all forms of healthcare and to make this information readily available to clinicians and other decision-makers at all levels of healthcare systems, http://www.cochrane.org/. The Cochrane Oral Health Review Group aims to produce systematic reviews that primarily include all RCTs of oral health. Oral health is broadly conceived to include the prevention, treatment, and rehabilitation or oral, dental, and craniofacial diseases and disorders, http://www.cochrane-oral.man.ac.uk/.

Cohort Study: A study in which patients who presently have a certain condition and/or receive a particular treatment are followed over time and compared with another group who are not affected by the condition under investigation. The disadvantage of cohort studies is they can take a very long time waiting for the conditions of interest to develop.

Critical Appraisal: The process of assessing and interpreting evidence by systematically considering its validity, results, and relevance to your own work.

Cross-Sectional Study: An observational study that examines a characteristic (or set of characteristics) and a health outcome in a sample of people at one point in time.

Double Blind Study: A double blind study is one in which neither the patient nor the physician knows whether the patient is receiving the treatment of interest or the control treatment. A double blind study is the most rigorous clinical research design because, in addition to the randomization of subjects that reduces the risk of bias, it can eliminate the placebo effect that is a further challenge to the validity of a study.

Evidence-Based Decision Making (EBDM): The use of current best evidence in making decisions about individual patient care. Evidence provides another dimension to the decision-making process that includes the clinical skills, judgment, and experience of the individual practitioner along with the patient's preferences.

Evidence-Based Practice (formerly Medicine): The integration of best research evidence with clinical expertise and patient values. Best research evidence refers to clinically relevant research, especially from patient-centered clinical research. Clinical expertise means the ability to use clinical skills and past experience to rapidly identify each patient's unique health state and diagnosis, individual risks and benefits of potential interventions, and personal values and expectations. Patient values refers to the unique preferences, concerns, and expectations that each patient brings to a clinical encounter which must be integrated into clinical decisions if they are to serve the patient. (Sackett D, Straus S, Richardson W, 2000)

Event Rate: The proportion of patients in a group in whom the event is observed. Thus, if out of 100 patients, the event is observed in 27, the event rate is 0.27. Control Event Rate (CER) and Experimental Event Rate (EER) are used to refer to this in control and experimental groups of patients respectively.

Gold Standard: A method, procedure, or measurement that is widely accepted as being the best available, e.g., used with studies when measuring the reliability of a particular diagnostic measure for a disease against the accepted measure as being the best for the same disease.

Limits [for searching]: Broad restrictions applicable to existing search sets; limits searches to specific fields such as language, human or animal publication types (clinical trial, meta-analysis, randomized controlled trial, practice guideline, reviews), age groups, gender, type of study, publication date, a specific language, types of articles, or subsets. Limits will differ among databases.

Literature or Narrative Reviews: Deals with a broad range of issues on a given topic rather than answering a specific question in depth as found in a systematic review. Narrative reviews can be a subjective assessment in that the literature can be selected to support a desired conclusion.

MeSH (Medical Subject Headings): The thesaurus for MEDLINE, a controlled vocabulary used as the indexing language, providing consistent terminology for concepts covered in the database.

Numbers Needed to Treat (NNT): The number of patients one would need to treat with the experimental treatment or intervention to achieve one additional patient who has a favorable response or outcome. For example, if a drug has an NNT of 15, it means 15 people would need to be treated with the drug to prevent one additional bad outcome. NNT is calculated as 100/absolute difference, NNT = 1/ARR.

MEDLINE: Produced by the U.S. National Library of Medicine, the MEDLINE database is widely recognized as the premier source for bibliographic and abstract coverage of biomedical literature. MEDLINE encompasses information from Index Medicus, Index to Dental Literature, and International Nursing, as well as other sources of coverage in the areas of allied health, biological and physical sciences, humanities, and information science as they relate to medicine and healthcare, communication disorders, population biology, and reproductive biology. More than 12 million records from more than 4,600 journals are indexed, plus selected monographs of congresses and symposia (1976-1981). Abstracts are included for about 67% of the records. http://www.ovid.com/documentation/user/field_guide/

Meta-analysis: A statistical process commonly used with systematic reviews. It involves combining the statistical analyses and summarizing the results of several individual studies into one analysis. When data from multiple studies are pooled, the sample size and power usually increase.

Odds: A ratio of events to non-events. If the event rate for a disease is 0.1 (10%), its non-event rate is 0.9 and, therefore, its odds are 1:9, or 0.111.

Odds Ratio: Describes the odds of an experimental patient suffering an adverse event relative to a control patient. To calculate the odds ratio, you need to know the odds for disease in each group. Odds are derived by dividing the event rate by the non-event rate for each group:
OR = (EER/(1-EER)) / (CER/(1-CER))

PICO: systematic process for converting information needs/problems into questions so they can be answered. A “well-built” question includes four parts that identify the patient problem or population (P), intervention (I), comparison (C), and outcome(s) (O), referred to as PICO, http://cebm.jr2.ox.ac.uk/docs/focusquest.html.

PubMed: PubMed was developed by the National Center for Biotechnology Information (NCBI) at the National Library of Medicine (NLM), located at the National Institutes of Health (NIH). It was developed in conjunction with publishers of biomedical literature as a search tool for accessing literature citations and linking to full-text journals at web sites of participating publishers. http://www.ncbi.nlm.nih.gov/PubMed/

Randomized Controlled Trial (RCT): A trial in which subjects are randomly assigned to two groups: one (the experimental group) receiving the intervention being tested and the other (the comparison group or controls) receiving an alternative treatment. The two groups are then followed up to see if any differences between them result.

Relative Risk Difference: The proportional difference between the rates of events in the experimental group and the control group, taking into account the control group rate. Relative differences are always bigger than absolute differences and often tend to inflate perceptions of what the results of the study truly are. The RRD is calculated by dividing the absolute difference by the control rate, (experimental rate-control rate)/control rate.

Relative Risk Reduction (RRR): The percent reduction in events in the treated group event rate (EER) compared to the control group event rate (CER): RRR = (CER - EER) / CER * 100.

Risk Ratio: The ratio of risk in the treated group (EER) to the risk in the control group (CER): RR = EER/CER. RR is used in randomized trials and cohort studies.

Sensitivity: Proportion of all the documents that are relevant that your search manages to find or the likelihood of retrieving relevant items (precision). Increase sensitivity if not retrieving enough by broadening the question, use “OR” with synonyms and related concepts. Find more search terms from relevant records using truncation, relevant items. Sensitivity of a diagnostic test refers to the proportion of truly diseased persons, as measured by the gold standard, who are identified as diseased by the test under study, http://cebm.jr2.ox.ac.uk/docs/searching.html#senspec

Specificity: Likelihood of excluding irrelevant items. Increase specificity if retrieving too much by narrowing the question and using more specific terms. Specificity of a diagnostic test refers to the proportion of truly non-diseased persons, as measured by the gold standard, who are so identified by the diagnostic test under study, http://cebm.jr2.ox.ac.uk/docs/searching.html#senspec

Sensitivity: The proportion of people with disease who have a positive test.
Sensitivity = a/(a+c)

Specificity: The proportion of people free of a disease who have a negative test.
Specificity = d/(b+d)

Likelihood Ratio: The likelihood a given test result would be expected in a patient with the target disorder compared to the likelihood the same result would be expected in a patient without that disorder.

LR+ = Sensitivity/(1-specificity) = [a/(a+c)] / b/(b+d)
LR- = (1 – sensitivity) /specificity = [c / (a+c)] / [d/(b+d)]

Positive Predictive Value (+PV): The proportion of people with a positive test who have the target disorder = a/(a + b)

Negative Predictive Value (-PV): The proportion of people with a negative test who do not have the target disorder = d/(c + d)

Systematic Reviews: Considered the gold standard for evidence, these reviews provide a summary of individual research studies that have investigated the same phenomenon or question. This scientific technique uses explicit criteria for retrieval, assessment, and synthesis of evidence from individual RCTs and other well-controlled methods. Systematic reviews provide a way of managing large quantities of information.

Validity: Validity refers to the soundness or rigor of a study. A study is valid if the way it is designed and carried out means the results are unbiased; that is, it gives you a 'true' estimate of clinical effectiveness.

Definitions Compiled from Several Sources:
Sackett D, Straus S, Richardson W. Evidence-Based Medicine: How to Practice & Teach EBM. 2000; London, England: Churchill Livingstone.

CEBM, Evidence-Based Medicine Glossary, http://cebm.jr2.ox.ac.uk/docs/glossary.html

McKibbon A, Eady A, Marks S. PDQ, Evidence-based Principles and Practice, BC Decker, Hamilton, Ontario, 1999.

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Citation Number: Vol. 4, No. 1, Page 050