## CTB Research Commitment

We maintain the highest standards in developing, executing and reporting assessments that serve the needs of every educator and learner.

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What is Item Response Theory? What are lexile scores? What is a valid test? Learn about these terms and more in this glossary of educational assessment terms.

**Mean**

The quotient obtained by dividing the sum of a set of scores by the number of scores; also called "average." Mathematicians call it "arithmetic mean."

**Median**

The middle score in a set of ranked scores. Equal numbers of ranked scores lie above and below the median. It corresponds to the 50th percentile and the 5th decile.

**Mixed-Format Tests**

An assessment that includes different forms of questions. The questions could include a mix of multiple choice, essays, or performance tasks.

**Mode**

The score or value that occurs most frequently in a distribution.

**Multiple Measures**

Assessments that measure student performance in a variety of ways. Multiple measures may include standardized tests, teacher observations, classroom performance assessments, and portfolios.

**Multiple-Choice Item**

A question, problem, or statement (called a "stem") which appears on a test, followed by two or more answer choices, called alternatives or response choices. The incorrect choices, called distractors, usually reflect common errors. The examinee's task is to choose from, among the alternatives provided, the best answer to the question posed in the stem. These are also called "selected-response items."

**Norm-Referenced Test**

A standardized assessment, in which all students perform under the same conditions. This type of test compares a student or group of students with a specified reference group, usually others of the same grade and age for K–12 students, or for adults, those with similar characteristics, such as those in an adult basic education class.

**Normal Distribution Curve**

A bell-shaped curve representing a theoretical distribution of measurements that is often approximated by a wide variety of actual data. It is often used as a basis for scaling and statistical hypothesis testing and estimation in psychology and education because it approximates the frequency distributions of sets of measurements of human characteristics.

**Norms**

The average or typical scores on a test for members of a specified group. They are usually presented in tabular form for a series of different homogeneous groups.

**Number Correct or "Raw" Score**

The Number of Correct Responses (NCR) is the number of items answered correctly by a student on any given test section.

We maintain the highest standards in developing, executing and reporting assessments that serve the needs of every educator and learner.

School districts come to us with varying needs and challenges. We help them make their students successful.