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Data - Raw, unsummarized, and unanalyzed facts and figures.

Data Mining Software - uses sophisticated decision-making processes to search raw data for patterns and relationships that may be significant.

Degrees of Freedom - A measure of how precise an estimate of variation is. It is defined as (n-1), or one less than the sample size.

Deontology - An ethical or moral reasoning framework that focuses on the welfare of the individual and that uses means, intentions, and features of the act itself in judging its ethicality; sometimes referred to as the rights or entitlements model.

Dependent (or Correlated) Sample t-test - Used to compare two means taken from the same sample, such as in a pretest/posttest situation.

Descriptive Statistics - Concerned with the mathematical techniques that are used to describe collected sample data.

Dichotomous Question - Fixed-alternative question in which respondents are asked to indicate which of two alternative responses most closely corresponds to their position on a subject.

Discrete Variables - Variables of which there is no possible value between adjacent units on the scale; there are separate, distinct measurements of a given characteristic. Examples are the frequency of any event, gender, and hair color. Nominal and ordinal variables are always discrete.

Discriminant Analysis - Statistical technique employed to model the relationship between a dichotomous or multichotomous criterion variable and a set of p predictor variables.

Disguise - Amount of knowledge about the purpose of a study communicated to the respondent by the data-collection method. An undisguised questionnaire, for example, is one in which the purpose of the research is obvious from the questions posed, whereas a disguised questionnaire attempts to hide the purpose of the study.

Disproportionate Stratified Sampling - Stratified sample in which the individual strata or subsets are sampled in relation to both their size and their variability; strata exhibiting more variability are sampled more than proportionately to their relative size, while those that are very homogeneous are sampled less than proportionately.

Distribution - A given set of values or measures of the same characteristic. An example is a list of the scores students in one class made on their last test.

Distribution of Sample Means - The collection of sample means for all the possible random samples of a particular size that can be obtained from a given population.

Double-Barreled Question - A question that calls for two responses and thereby creates confusion for the respondent.