Glossary of Terms

We know that many of the concepts used on this site can be difficult to understand. For that reason, we have provided you with a glossary to help you make sense of the terms used in Comparative Effectiveness Research. Every word that is defined in this glossary should appear highlighted throughout the Web site. When you come upon a highlighted term and would like to read the full definition, you can either click on the word to visit the glossary or roll your mouse over the word for a pop-up definition.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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. detail

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. detail

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. detail