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Adam SS, McDuffie JR, Ortel TL, et al. Comparative Effectiveness of Warfarin and Newer Oral Anticoagulants for the Long-Term Prevention and Treatment of Arterial and Venous Thromboembolism [Internet]. Washington (DC): Department of Veterans Affairs (US); 2012 Apr.


Abstract screening

The stage in a systematic review during which titles and abstracts of articles identified in the literature search are screened for inclusion or exclusion based on established criteria. Articles that pass the abstract screening stage are promoted to the full-text review stage.

A registry and results database of federally and privately supported clinical trials conducted in the United States and around the world. provides information about a trial’s purpose, location, and participant characteristics among other details.

Cochrane Database of Systematic Reviews

A bibliographic database of peer-reviewed systematic reviews and protocols prepared by the Cochrane Review Groups in The Cochrane Collaboration.

Companion article

A publication from a trial that is not the article containing the main results of that trial. It may be a methods paper, a report of subgroup analyses, a report of combined analyses, or other auxiliary topic that adds information to the interpretation of the main publication.

Confidence interval (CI)

The range in which a particular result (such as a laboratory test) is likely to occur for everyone who has a disease. “Likely” usually means 95 percent of the time. Clinical research studies are conducted on only a certain number of people with a disease rather than all the people who have the disease. The study’s results are true for the people who were in the study but not necessarily for everyone who has the disease. The CI is a statistical estimate of how much the study findings would vary if other different people participated in the study. A CI is defined by two numbers, one lower than the result found in the study and the other higher than the study’s result. The size of the CI is the difference between these two numbers.

Cytochrome P-450 (CYP) enzyme system

A family of liver enzymes that serve two major functions: (1) biosynthesis of steroids, fatty acids, and bile acids and (2) metabolism of endogenous and a wide variety of exogenous substrates, such as toxins and drugs. They are classified into CYP gene family and subfamilies; for example, CYP1, CYP2 and CYP3 are responsible for most drug metabolism.

Data abstraction

The stage of a systematic review that involves a pair of trained researchers extracting reported findings specific to the research questions from the full-text articles that met the established inclusion criteria. These data form the basis of the evidence synthesis.

Deep vein thrombosis (DVT)

A blood clot that develops in the deep veins of the legs.

Direct thrombin inhibitors (DTIs)

A new class of anticoagulants that bind directly to thrombin and block its interaction with its substrates.


An online application designed specifically for the screening and data extraction phases of a systematic review.

Efflux transporter p-glycoprotein

Transporters that pump out unwanted toxic substances through specific efflux pumps. P-glycoprotein is the most common efflux transporter that allows drug molecules to pass through membranes.


The Excerpta Medica database (EMBASE) produced by Elsevier, a major biomedical and pharmaceutical database indexing over 3500 international journals in the following fields: drug research, pharmacology, pharmaceutics, toxicology, clinical and experimental human medicine, health policy and management, public health, occupational health, environmental health, drug dependence and abuse, psychiatry, forensic medicine, and biomedical engineering or instrumentation. There is selective coverage for nursing, dentistry, veterinary medicine, psychology, and alternative medicine.

Exclusion criteria

The criteria, or standards, set out before a study or review. Exclusion criteria are used to determine whether a person should participate in a research study or whether an individual study should be excluded in a systematic review. Exclusion criteria may include age, previous treatments, and other medical conditions.

Factor Xa (FXa) inhibitor

A new class of anticoagulants that bind directly to factor Xa and block its interaction with other substrates.

Full-text review

The stage of a systematic review in which a pair of trained researches evaluates the full-text of study articles for potential inclusion in the review.


Grading of Recommendations Assessment, Development, and Evaluation (GRADE), a system of assessing the quality of medical evidence and evaluating the strength of recommendations based on the evidence.

Inclusion criteria

The criteria, or standards, set out before the systematic review. Inclusion criteria are used to determine whether an individual study can be included in a systematic review. Inclusion criteria may include population, study design, sex, age, type of disease being treated, previous treatments, and other medical conditions.

Mitral stenosis

A heart valve disorder that involves the mitral valve, which separates the upper and lower chambers on the left side of the heart. Stenosis refers to a condition in which the valve does not open fully, restricting blood flow.

Nonvalvular atrial fibrillation (AF)

An abnormal cardiac rhythm that occurs at the absence of mitral stenosis. AF is characterized by rapid uncoordinated firing of electrical impulses in the upper chambers of the heart (atria), which prevents the blood from being effectively pumped into lower chamber of the heart (ventricles).

Optimal information size

The number of patients that need to be included in a pooled analysis (meta-analysis) to provide sufficient power to detect the smallest clinically important difference in treatment effect.


Preferred Reporting Items for Systematic Reviews and Meta-Analyses, an evidence-based minimum set of items for reporting in systematic reviews and meta-analyses.

Publication bias

The tendency of researchers to publish experimental findings that have a positive result, while not publishing the findings when the results are negative or inconclusive. The effect of publication bias is that published studies may be misleading. When information that differs from that of the published study is not known, people are able to draw conclusions using only information from the published studies.


A database of citations for biomedical literature from MEDLINE®, life science journals, and online books in the fields of medicine, nursing, dentistry, veterinary medicine, the health care system, and preclinical sciences.

Pulmonary embolism (PE)

Blocking of the pulmonary artery (lungs) or one of its branches by a clot.

Randomized controlled trial

A prospective, analytical, experimental study using primary data generated in the clinical environment. Individuals similar at the beginning of the trial are randomly allocated to two or more treatment groups and the outcomes the groups are compared after sufficient followup time. Properly executed, the RCT is the strongest evidence of the clinical efficacy of preventive and therapeutic procedures in the clinical setting.


Review Manager, a software program used for preparing and maintaining Cochrane systematic reviews.


A way of expressing the chance that something will happen. It is a measure of the association between exposure to something and what happens (the outcome). Risk is the same as probability, but it usually is used to describe the probability of an adverse event. It is the rate of events (such as breast cancer) in the total population of people who could have the event (such as women of a certain age).

Statistical significance

A mathematical technique to measure whether the results of a study are likely to be true. Statistical significance is calculated as the probability that an effect observed in a research study is occurring because of chance. Statistical significance is usually expressed as a P-value. The smaller the P-value, the less likely it is that the results are due to chance (and more likely that the results are true). Researchers generally believe the results are probably true if the statistical significance is a P-value less than 0.05 (p<.05).

Strength of evidence (SOE)

A measure of how confident reviewers are about decisions that may be made based on a body of evidence. SOE is evaluated using one of four grades: (1) High confidence that the evidence reflects the true effect; further research is very unlikely to change reviewer confidence in the estimate of effect; (2) moderate confidence that the evidence reflects the true effect; further research may change the confidence in the estimate of effect and may change the estimate; (3) low confidence that the evidence reflects the true effect; further research is likely to change the confidence in the estimate of effect and is likely to change the estimate; and (4) insufficient; the evidence either is unavailable or does not permit a conclusion.

Systematic review

A summary of the clinical literature. A systematic review is a critical assessment and evaluation of all research studies that address a particular clinical issue. The researchers use an organized method of locating, assembling, and evaluating a body of literature on a particular topic using a set of specific criteria. A systematic review typically includes a description of the findings of the collection of research studies. The systematic review may also include a quantitative pooling of data, called a meta-analysis.

Venous thromboembolism (DVT/PE)

Obstruction of a vein or veins (embolism) by a blood clot (thrombus) in the blood stream.

Vitamin K antagonist (warfarin)

An anticoagulant that acts by inhibiting the synthesis of vitamin K-dependent coagulation factors; i.e., I, VII, IX and X.

Cover of Comparative Effectiveness of Warfarin and Newer Oral Anticoagulants for the Long-Term Prevention and Treatment of Arterial and Venous Thromboembolism
Comparative Effectiveness of Warfarin and Newer Oral Anticoagulants for the Long-Term Prevention and Treatment of Arterial and Venous Thromboembolism [Internet].
Adam SS, McDuffie JR, Ortel TL, et al.
Washington (DC): Department of Veterans Affairs (US); 2012 Apr.

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