Glossary

Talking about treatment options with your doctor may include a lot of language that may be confusing. Here are a few definitions that may help.

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Absolute Risk

The probability or chance that a person will have a medical event. Absolute risk is expressed as a percentage. It is the ratio of the number of people who have a medical event divided by all of the people who could have the event because of their medical condition. Read more.

Adverse Drug Reaction

A bad or harmful reaction to a drug that is used to treat or prevent a disease. Read more.

Adverse Effect

Anything that a person might feel is a negative or harmful result of a treatment or test. Read more.

Adverse Event

Any negative or unwanted effect from any drug, device, or medical test. Read more.

Adverse Reaction

Any negative or unwanted effect from a drug, device, or medical test. Read more.

Analysis

The process of preparing the results or conclusions of a study. An analysis usually is performed by doing mathematical calculations known as statistics. Read more.

Association

A relationship. In research studies, association means that two characteristics (sometimes also called variables or factors) are related so that if one changes, the other changes in a predictable way. An association does not necessarily mean that one variable causes the other. Read more.

Bias

Any factor, recognized or not, that distorts the findings of a study. In research studies, bias can influence the observations, results, and conclusions of the study and make them less accurate or believable. Read more.

Black Box Warning

An advisory from the U.S. Food and Drug Administration (FDA) that tells health care professionals and consumers that a drug might be very dangerous for some people. The FDA is the U.S. Government agency that regulates and monitors drugs and medical devices to make sure they are safe and effective. Read more.

Blinding

A way of making sure that the people involved in a research study — participants, clinicians, or researchers — do not know which participants are assigned to each study group. Blinding usually is used in research studies that compare two or more types of treatment for an illness. Blinding is used to make sure that knowing the type of treatment does not affect a participant's response to the treatment, a health care provider's behavior, or assessment of the treatment effects. Read more.

Clinical Research

The branch of medical science devoted to finding information that improves people's health. It includes research studies that examine the safety and effectiveness of medications, medical devices, diagnostic tests, and treatment regimens intended for human use. Usually, more than one person with the same disease is studied. Read more.

Clinical Trial

A carefully conducted research study that compares the effects of drugs, treatments, or diagnostic tests. Read more.

Cohort

A group of people with some characteristic in common. The characteristic can be:

• Where people live.
• Where they work.
• Where they go to school.
• People of the same age.
• People with the same medical condition.
• People receiving the same medical treatment.

Read more.

Cohort Study

A clinical research study in which people who presently have a certain condition or receive a particular treatment are followed over time and compared with another group of people who are not affected by the condition. Read more.

Comparative Effectiveness

A type of health care research that compares the results of one approach for managing a disease to the results of other approaches. Comparative effectiveness usually compares two or more types of treatment, such as different drugs, for the same disease. Comparative effectiveness also can compare types of surgery or other kinds of medical procedures and tests. The results often are summarized in a systematic review. Read more.

Confidence Interval

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 confidence interval is a statistical estimate of how much the study findings would vary if other different people participated in the study. A confidence interval 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 confidence interval is the difference between these two numbers. Read more.

Control Group

In a research study, the group of people who do not receive the treatment being tested. The control group might receive a placebo, a different treatment for the disease, or no treatment at all. Read more.

Controlled Clinical Trial

A type of clinical trial comparing the effectiveness of one medication or treatment with the effectiveness of another medication or treatment. In many controlled trials, the other treatment is a placebo (inactive substance) and is considered the "control." Read more.

Cost-Benefit Analysis

A type of analysis that compares the financial costs with the benefits of two or more health care treatments or programs. Health care interventions that have the same or better benefit at a lower cost are better values than treatments or programs that are more expensive. Read more.

Cost-Effectiveness Analysis

A type of analysis that is similar to a cost-benefit analysis but is used when the benefits cannot be measured in financial terms or dollars. It would be hard to put a price-tag on living an extra year of life. Read more.

Data

In clinical research, the information recorded about a participant in a study. There are many different kinds of data. Read more.

Diagnostic Test

A procedure to provide information about a person's condition that helps health care providers to make a diagnosis. Diagnostic tests provide information about whether a person does or does not have a particular disease. Read more.

Drug

A medicine (chemical compound) used to prevent, diagnose, or treat conditions. Some drugs need a prescription from a physician or nurse practitioner and other drugs do not need a prescription. Read more.

Drug Product

A manufactured product that contains a drug. There are many forms of drug products, including tablets (pills), capsules, creams, or liquids. A drug product often includes other chemicals that are not harmful to most people. They are included in the product for such reasons as making a liquid taste better or binding a tablet together so that it does not crumble in the bottle. Read more.

Effect Size

The amount of change in a condition or symptom because of a treatment (compared to not receiving the treatment). It is commonly expressed as a risk ratio (relative risk), odds ratio, or difference in risk. Read more.

Effective Dose

The amount of a drug most people need to take to control a disease or the symptoms of a disease. A dose lower than the effective dose would not bring about the outcome (such as relieving symptoms). Read more.

Effectiveness

Whether a drug or other treatment works in real life. Effectiveness studies of drugs look at whether they work when they are used the way that most people take them. Effectiveness means that most people who have the disease would improve if they used the treatment. Read more.

Efficacy

Whether a drug or other treatment works under the best possible conditions. In a research study about efficacy, the study participants are carefully selected, and the researchers can make sure the drug is taken properly and stored properly. The study participants may differ from other people in the general public who have the disease. A treatment that has efficacy under the best conditions may not work as well in a different group of people with the same disease. Read more.

Epidemiology

The field of science that studies the factors causing diseases, illnesses, or injuries in populations or community groups. Read more.

Evidence Table

A summary of the most important information from a group of research studies. An evidence table can include information on the number of participants in the research trials and the type and frequency of adverse events that participants had while taking the drugs being studied. Read more.

Evidence-Based Practice

Applying the best available research results (evidence) when making decisions about health care. Health care professionals who perform evidence-based practice use research evidence along with clinical expertise and patient preferences. Systematic reviews (summaries of health care research results) provide information that aids in the process of evidence-based practice. Read more.

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. Criteria help identify suitable participants. Read more.

External Validity

The extent to which clinical research studies apply to broader populations. A research study has external validity if its results can be generalized to the larger population. Read more.

Gold Standard Test

The diagnostic test that is considered the most accurate test for a particular condition. If the gold standard test is positive, it is highly likely that the person has the disease. If the gold standard test is negative, it is highly likely that the person does not have the disease. Read more.

Head-to-Head Trial

A study of two drugs or treatments that compares the effects of one treatment with the other. In a head-to-head trial, two groups of people with the same disease are compared. One group receives one treatment, and the second group receives the other. Read more.

Health Care Intervention

Any type of treatment, preventive care, or test that a person could take or undergo to improve health or to help with a particular problem. Health care interventions include drugs (either prescription drugs or drugs that can be bought without a prescription), foods, supplements (such as vitamins), vaccinations, screening tests (to rule out a certain disease), exercises (to improve fitness), hospital treatment, and certain kinds of care (such as physical therapy). Read more.

Heterogeneity

Differences among research studies. Heterogeneity can apply to either the way the studies were conducted, the methodologies used in the studies, or differences in the way people respond to the treatment. Research reports may describe different types of heterogeneity: Read more.

Human Subject

A person who participates in a research study or clinical trial. The person agrees to take part in the study and has been told about the possible dangers and benefits of participation. The participation can include different activities, depending on the goals of the study. Read more.

Hypothesis

A scientific idea that can be tested in a research study. The hypothesis is the scientific idea that led to the research study. Read more.

Inclusion Criteria

The criteria, or standards, set out before a study or review. Inclusion criteria are used to determine whether a person can participate in a research study or whether an individual study can be included in a systematic review. Inclusion criteria may include gender, age, type of disease being treated, previous treatments, and other medical conditions. Inclusion criteria help identify suitable participants. Read more.

Informed Consent

An agreement to receive a treatment or medical procedure. Before a person receives a proposed treatment or medical procedure, he or she must give informed consent. This means that the person must not only agree to the treatment, but also understand what he or she is agreeing to. Read more.

Internal Validity

The extent to which the results of a clinical research study are not biased. Several characteristics of a study affect its internal validity. Are the two groups of people being compared similar in all the important characteristics that may affect the measurements of data? Are the data collected being measured using accurate methods? Read more.

Life Expectancy

The average amount of time a person will live after a certain starting point, like birth or the diagnosis of a disease. The calculation is based on statistical information comparing people with similar characteristics, such as age, gender, race/ethnicity, and health. Read more.

Likelihood Ratio

A measure of the accuracy of a diagnostic test. It is used to determine how likely it is that a person has a specific disease based on test results. When the test result is positive, the likelihood ratio is known as a positive likelihood ratio (LR+). When the test result is negative, the likelihood ratio is known as a negative likelihood ratio (LR-). The likelihood ratio is a way of comparing the probability that the test result would occur in people with the disease as opposed to occurring in people without the disease.

Read more.

Masking

A way of making sure that the people involved in a research study — participants, clinicians, or researchers — do not know which participants are assigned to each study group. Masking usually is used in research studies that compare two or more types of treatment for an illness. Masking is used to make sure that knowing the type of treatment does not affect a participant's response to the treatment, a health care provider's behavior, or assessment of the treatment effects. Read more.

Meta-Analysis

A way of combining data from many different research studies. A meta-analysis is a statistical process that combines the findings from individual studies. Read more.

Mortality

The number of people who die. Mortality is usually measured for people who have something in common, such as having a particular disease or being of a certain age. Read more.

Negative Predictive Value

Indicates the likelihood that people with a negative test result would not have a condition. The higher the value of the negative predictive value (for example, 99 percent would usually be considered a high value), the more useful the test is for predicting that people do not have the condition. Read more.

Number Needed to Harm

The number of people who would need to be treated over a specific period of time before one bad outcome of the treatment will occur. The number needed to harm (NNH) for a treatment can be known only if clinical trials of the treatment have been performed. Read more.

Number Needed to Treat

The number of people who need to be treated over a specific period of time to promote one additional good outcome (or prevent one additional bad outcome). The number needed to treat (NNT) for a treatment can be known only if clinical trials of the treatment have been performed. Read more.

Odds Ratio

The chance of an event occurring in one group compared to the chance of it occurring in another group. The odds ratio (OR) is a measure of effect size and is commonly used to compare results in clinical trials. Read more.

Off-Label Use

The practice of prescribing a drug for a condition not listed on the U.S. Food and Drug Administration (FDA) label. The label lists the medical conditions for which the FDA has approved the drug. Off-label uses may be supported by clinical evidence not available or not submitted to the FDA. Accepted medical practice often includes off-label use. Read more.

Open-Label Study

A clinical research study in which the participant, health care professional, and others know the drug and dose being given. The research study is not "blinded." Read more.

OTC

A term used to describe drugs you can buy without a prescription. Read more.

Outcome

The end result of health care practices. There are many kinds of outcomes. How long people live following a health care treatment is one kind of outcome, known as side effects of drugs. Another type of outcome is whether people needed to change to another kind of treatment. Read more.

Over-the-Counter

A term used to describe drugs you can buy without a prescription. Read more.

Patient

An individual seeking or receiving medical care. Read more.

Placebo

An inactive substance commonly called a "sugar pill." In a clinical trial, a placebo is designed to look like the drug being tested and is used as a control. It does not contain anything that could harm a person. Read more.

Placebo Controlled Study

A study in which the effect of a drug is compared with the effect of a placebo (an inactive substance designed to resemble the drug). In placebo controlled clinical trials, participants receive either the drug being studied or a placebo. The results of the drug and placebo groups are then compared to see if the drug is more effective in treating the condition than the placebo is. Read more.

Placebo Effect

A physical or emotional change that occurs after a participant in a research study takes a placebo. The change, which may include the lessening of symptoms, is not the result of chemical effects of the placebo because the placebo does not contain any active ingredients. The change is often based on the participant's or researcher's expectation that a change will occur. Read more.

Pooled Odds Ratio

When the data on odds ratios from multiple studies are combined, the result is a pooled odds ratio (POR). An odds ratio (OR) is the comparison of the chance of an event occurring in one group to the chance of it occurring in another group. The odds ratio is a measure of effect size and is commonly used to compare results in clinical trials. Read more.

Positive Predictive Value

Indicates the likelihood that a person with a positive test result would actually have the condition for which the test is used. The higher the value of the positive predictive value (for example, 90 percent would be considered a high value), the more useful the test is for predicting that the person has the condition. Read more.

Pretest Probability

The probability that a person has a particular disease before any test results are obtained. The pretest probability for large groups of people (such as the population of a city) is the same as the prevalence of the disease in that group. Read more.

Prevalence

How often or how frequently a disease or condition occurs in a group of people. Prevalence is calculated by dividing the number of people who have the disease or condition by the total number of people in the group. Read more.

Prior Probability

The probability that a person has a particular disease before any test results are obtained. The prior probability for large groups of people (such as the population of a city) is the same as the prevalence of the disease in that group. Read more.

Probability

The likelihood (or chance) that an event will occur. In a clinical research study, it is the number of times a condition or event occurs in a study group divided by the number of people being studied. Read more.

Prognosis

The way a health situation is likely to turn out. Prognosis refers to the usual progression and outcome of a condition. Read more.

Prospective Observational Study

A clinical research study in which people who presently have a certain condition or receive a particular treatment are followed over time and compared with another group of people who are not affected by the condition. Read more.

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. Read more.

Randomization

A method of assigning participants in clinical trials into two or more groups randomly (by chance). One group receives the treatment or drug being researched, and one group receives either no treatment, a placebo (inactive substance), or another drug. Participants are assigned to a group by various methods. Read more.

Randomized Controlled Trial

A controlled clinical trial that randomly (by chance) assigns participants to two or more groups. There are various methods to randomize study participants to their groups. Read more.

Relative Risk

A comparison of the risk of a particular event for different groups of people. Relative risk (RR) is usually used to estimate exposure to something that could affect health. In a clinical research study, the experimental group is exposed to a particular drug or treatment. The control group is not. The number of events in each group is compared to determine relative risk. Read more.

Risk

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). Read more.

Risk Factor

A characteristic of a person that affects that person's chance of having a disease. A risk factor may be an inherent trait, such as gender or genetic make-up, or a factor under the person's control, such as using tobacco. A risk factor does not usually cause the disease. It changes a person's chance (or risk) of getting the disease. Read more.

Risk/Benefit Ratio

A method for comparing a treatment's benefits and risks, such as curing a disease (benefit) versus having a serious side effect from the treatment (risk). The risk/benefit ratio of a treatment is different depending on the disease or condition being treated. Read more.

Sample Size

The number of people included in a drugs) will be detected. Read more.

Screening

Using tests or other methods of diagnosis to find out whether or not a person has a specific disease or condition before it causes any symptoms. For many diseases (for example, cancers), starting treatment earlier leads to better results. The purpose of screening is to find the disease so that treatment can be started as early as possible. Read more.

Selection Bias

A type of bias caused by an error in the way people are assigned to groups in a clinical research study. This can occur when the study and control groups are chosen so that they differ from each other in ways that may affect the outcome of the study. Read more.

Sensitivity

The ability of a test to identify correctly people with a condition. A test with high sensitivity will nearly always be positive for people who have the condition (the test has a low rate of false-negative results). Sensitivity is also known as the true-positive rate. Read more.

Side Effects

Any effects of a drug or treatment that are not wanted. Side effects may be temporary and go away when the drug is stopped. Sometimes they continue for a longer time, even when the drug is no longer being taken. Read more.

Specificity

The ability of a test to identify correctly people without a condition. A test with high specificity will rarely be wrong about who does NOT have the condition (the test has a low rate of false-positive results). Specificity is also known as the true-negative rate. Read more.

Standard Treatment

The treatment or procedure that is most commonly used to treat a disease or condition. In clinical trials, new or experimental treatments sometimes are compared to standard treatments to measure whether the new treatment is better. Read more.

Statistical Analysis

The process of preparing the results or conclusion of a study. A statistical analysis usually is performed by doing mathematical calculations known as statistics. Read more.

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). Read more.

Study

A research process in which information is recorded for a group of people. The information is known as data. The data are used to answer questions about a health care problem. Read more.

Study Population

The group of people participating in a clinical research study. The study population often includes people with a particular problem or disease. It may also include people who have no known diseases. Read more.

Survival

The length of time people live. Survival can show whether treatments for a disease can prevent or delay death. Survival is usually expressed in terms of how long the people in a group remain alive. It sometimes is summarized by calculating an average. Survival also can be summarized by the number of people who are still alive after a certain length of time, such as 5 years later. Read more.

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. Read more.

Treatment Effect

The amount of change in a condition or symptom because of a treatment (compared to not receiving the treatment). It is commonly expressed as a risk ratio (relative risk), odds ratio, or difference in risk. Read more.

True-Negative Rate

The ability of a test to identify correctly people without the condition. A test with a high true-negative rate will rarely be wrong about who does NOT have the condition (the test has a low rate of false-positive results). The true-negative rate is also known as specificity . Read more.

True-Positive Rate

The ability of a test to identify correctly people with a condition. A test with a high true-positive rate will will nearly always be positive for people who have the condition (the test has a low rate of false-negative results). The true-positive rate is also known as sensitivity. Read more.

Validity

Whether a test or technique actually measures what it is intended to measure. Validity can refer to an individual measurement or to the design and approach taken in a clinical research study. When referring to a single measurement, validity means the accuracy of the measurement. Read more.

Variable

Any characteristic that can be measured in different individuals. A variable is also any factor that can affect the outcome of an experiment or study. Read more.