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Lambda
A measure of association; a statistic used with nominal variables.

Level of Measurement
Refers to the four levels of variables and their empirical attributes - nominal, ordinal, interval, and ratio.

Likert Scale
A type of composite measure using standardized response categories in survey questionnaires. Typically a range of questions using response categories such as strongly agree, agree, disagree, and strongly disagree are utilized to construct a composite measure.

Logic Model
Describes how a program should work, presents the planned activities for the program, and focuses on anticipated outcomes. While logic models present a theory about the expected program outcome, they do not demonstrate whether the program caused the observed outcome. Diagrams or pictures that illustrate the logical relationship among key program elements through a sequence of "if-then" statements are often used when presenting logic models.

Longitudinal Data
Sometimes called "time series data," observations collected over a period of time; the sample (instances or cases) may or may not be the same each time but the population remains constant. FOR EXAMPLE, quarterly arrest rates for drug-related offenses in a given city for a period of two years.

Longitudinal Study
The study of the same group over a period of time. These generally are used in studies of change.