The following are explanations of terms used in Health Compass. There are many other glossaries and dictionaries of research and medical terms available on the Internet.

Here are a few sites that contain glossaries of additional research and medical terms:

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To search for a particular term, click on the first letter of the word, above, or scroll through the glossary to find the term you are looking for.


Abstract - A brief summary of a research study, containing a short description of the study purpose, methods, and results, usually found at the beginning of an article reporting on a study. Reading just the abstract may be misleading, because it is not possible to include all the details about a study in the abstract.

Advance directive - Any spoken or written decision with instructions and preferences for medical treatment. A health care proxy directive indicates who you want to make decisions about your care if you are too sick or otherwise unable to make decisions for yourself.

Adverse event - Any unwanted, unpleasant, negative, or dangerous effect in response to a treatment or intervention (also referred to as an adverse effect, adverse reaction or side effect).

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Bias - Something that can distort or falsify the results of a study. When individuals in a study are asked to recall events or behaviors, some will report the information more accurately than others. This is referred to as reporting bias. (See also selection bias)

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Causality - The relationship between an event and the factor(s) that contributed to the cause or occurrence of the event; the relationship between cause and effect.

Citation - Listing of an article by title, author's name, publication name, publication date, and other details. Assists readers in locating the article.

Clinical guidelines - Statements developed through a specific process that are designed to assist health practitioners and patients in making appropriate health care decisions about a specific condition or treatment. Clinical guidelines are usually developed under the auspices of a medical association or government agency by a panel of experts, and are based on a thorough review of scientific studies on the topic being addressed.

Clinical significance (or importance) - The extent to which the results of a study will be important, useful, and applicable in the treatment of patients.

Clinical trials - Experiments designed to test the effectiveness of a treatment or intervention. The term "clinical trial" often refers to specific experiments to test a new compound for potential use as a pharmaceutical or clinical agent. To conduct this type of clinical trial, an Investigational New Drug (IND) Application must be filed with the Food and Drug Administration (FDA). If the FDA accepts the IND, clinical trials in human subjects can be conducted. There are several phases of clinical trials before a drug is approved by the FDA.

Comparison group - A group of study participants who do not receive a treatment or intervention that is compared against a group that is receiving the intervention. The use of a comparison group implies that the study is not a randomized controlled study (see controlled study and randomized study).

Complementary and alternative medicine (CAM) - Health care practices and approaches that are not presently considered to be part of traditional or conventional medicine, ie, medical practices that are not commonly prescribed by licensed doctors and other health care providers.

Conclusions - In relation to reports on research studies, conclusions are the statements the researchers make about the outcomes of the research, based on their professional interpretation of the study or experiment results.

Confidence interval - A research study or experiment can show absolutely only the outcomes or results for the study participants themselves; the study results may not be true for others. The confidence interval (CI) is a mathematical description of how likely it is that others will have the same result as the study participants. The CI occurs between a lowest possible limit and a highest possible limit. The narrower the range between these two limits, the greater the likelihood that the results of the study can be applied to others.

Consensus - A collective opinion or general agreement.

Consensus statement - A report, usually by experts in the field, evaluating the available scientific information and data on a given biomedical or health intervention, often for the purpose of resolving a particular controversial issue in clinical practice.

Controlled study - A study in which there is a "control" group. This can be a group that is receiving a placebo (see placebo) or a conventional or standard treatment that is being compared with a new treatment. In a case-control study, the "control" group consists of people who do not have the condition being studied, and the "case" group consists of people who do have the condition.

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Double-blind study - A study in which neither the study subjects (participants) nor the experimenters (researchers) know which treatment or intervention any particular participant is receiving during the study.

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Evidence-based - A term applied to health care practices that are based on the review of the current best evidence on the effectiveness of a test, drug, surgery or other medical practice. This evidence is based on collecting and analyzing all of the research studies that have been conducted on a particular intervention. These reviews (see meta-analysis and systematic review) are often published or made available in electronic formats for wide distribution to health care providers and others.

Experimental study - A study in which the investigators determine and control the conditions of the experiment (see also interventional study).

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Generalizability - Whether or not the study results can be applied to or are relevant for a larger population or group than the group being studied.

Geriatrics - The branch of medicine that deals with the conditions, illnesses, and syndromes that generally occur in later life, and focuses on maintaining function as long as possible. A geriatrician is a physician who has had additional, specialized training in the medical care of older adults.

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Intervention group - Group in which study participants are assigned to receive the intervention under study (drug, test, procedure, etc).

Interventional study - Another term for experimental study, in which the experimenter determines and controls the intervention in the study.

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Meta-analysis - A statistical technique that combines the results of two or more studies of similar design; the statistical analysis of a large collection of results from individual studies for the purpose of integrating the findings. Integrating the study findings results in a larger sample size (number of study participants) than the sample size of each individual study, which may add to the statistical significance (see statistical significance) and generalizability (see generalizability) of the findings. The conclusions that can be drawn based on the data of a meta-analysis may be limited by such factors as differences in the designs of the individual studies being combined.

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Observational study - A study in which the investigator observes the effect of a risk factor (see risk factor), diagnostic test, or treatment on a particular outcome, eg, the relationship between smoking and heart attacks. In an observational study, the researchers examine and report on what is happening, without controlling the course of events.

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P-value - The p (probability) value shows how likely it is that the results of an experiment have occurred randomly (by chance). For example, if the p value is 0.05 this means that there is a 5% chance that the results could have been produced by random factors rather than by the intervention.

Peer-reviewed - Refers to a research report or "paper" that has been read and evaluated by experts in the topic. "Peer-reviewed journals" are those in which all the published articles have been reviewed by experts and determined to be of a quality and completeness that makes them acceptable for publication and distribution.

Placebo - An inactive pill, liquid, or powder that has no treatment value (a "sugar pill"). In a placebo-controlled trial, a new treatment being studied is given to one group, and a placebo to another group, to compare the effectiveness of the two (see controlled study). Ethical guidelines for conducting research experiments dictate that no sick person will receive a placebo if there is a known beneficial treatment. A "placebo-controlled study" is one in which the control group receives a placebo and the other group receives the treatment being studied.

Probability - The chance or likelihood of an event occurring.

Prospective study - A study that is designed ahead of time, in which study participants are selected, assigned to groups, and examined according to the design of the experiment. (See also retrospective study)

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Quantify (or quantitative research) - Describing research results or the variables in a research study numerically. This is contrasted with "qualify" or "qualitative research," which refers to variables or results that are difficult to express as numerical terms or categories.

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Randomized study - A study in which the participants in the study groups (comparison groups, groups receiving different treatments) are selected by chance (randomly). The results of such studies are generally thought to be more reliable than those of studies that are not randomized, because there is less chance that the study will be biased (see Bias).

Results - The specific outcomes of a study, often put in mathematical terms; different from conclusions, which are the researchers' interpretation of the results.

Retrospective study - A study in which the outcomes in a group of people are analyzed after the outcomes have occurred, by looking back in time from the present. One example is a study in which the medical histories of a group of people who all have the same condition are examined, to determine what similarities there may be in their medical backgrounds. (See also prospective study.)

Risk factors - Factors that have been shown (through data collection and research) to be associated with the development of a particular medical condition (eg, smoking is a risk factor for lung cancer).

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Sample size - The specific size of the group or groups being studied. Generally, the larger the sample size, the more reliable the study results, and the more likely it is that the results can be applied to larger groups of people.

Search engine - An Internet service that enables users to locate Web pages related to a specific topic or category (some examples are,,,

Searchable database - An online service that enables the user to search for a topic, category, or publication using a number of different search terms or criteria, such as author's name, publication date, publication title, etc. Data bases often consolidate records previously stored separately (some examples of research and health information databases are MedLine Plus:, and PubMed:

Selection bias - Distortion or falsification of study results (bias) that can occur when study subjects are assigned to groups.

Statistical significance - Refers to the probability or likelihood that an event occurred by chance alone. The results of a study are said to be statistically significant if the probability that the results occurred by chance is less than 0.05 (that is fewer than 1 chance in 20). In medical research, the level of statistical significance can depend on factors such as the number of study participants and the magnitude of the differences in outcomes observed between study participants.

Statistics - the mathematics of the collection, organization and interpretation of numerical data.

Study design - The science and art of planning how an experiment will be conducted to get the most valid and reliable results (also referred to as research or experimental design).

Subject directory - An Internet service in which a group selects and organizes Web sites by subject (some examples are and

Subjective - In relation to research studies, the interpretation of findings that are difficult to describe in numeric or concrete terms.

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Validity - the extent to which a measurement or finding is true or appropriate.

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