Glossary Items Starting with "D"

data: Plural noun that refers to information gathered in research. Conclusions are drawn on the basis of an evaluation of the data.
data-analysis phase of research: Research phase in which data gathered from observing participants are statistically analyzed.
data snooping: Type of secondary analysis of data to help generate hypotheses for further study.
debriefing: Disclosing to participants the full nature of a study that uses deception.
deception: Procedures used in research to hide from the participant the true nature of the study. Many studies require deception to prevent subject expectancy effects, but the use of deception raises ethical issues. Ethical use of deception requires complete debriefing of the participants at the end of the study.
decision tree: An organized pathway of ideas leading to a defined goal, in which at various points a decision is made about which of two or more "branches" to follow to the next decision point.
decision-tree flowchart: Flowchart model in which answers to specific questions lead to branching to a new set of questions or procedures. Appendix D presents a decision-tree model for selecting appropriate statistical tests.
decision-tree model: See decision-tree flowchart.
deductive reasoning: Reasoning from the general to the particular. In deductive reasoning, specific predictions are made about future events based on theories.
deductive theory: A theory that emphasizes constructs and the relationship between constructs and seeks to make predictions from the theory that can be tested with empirical research. Often contrasted with inductive theory and functional theory.
degrees of freedom (df): A statistical concept. One degree of freedom is lost each time a population parameter is estimated on the basis of a sample. The distribution of most statistics are tabled by degrees of freedom.
delayed-treatment control group: See waitlist control group.
demand characteristics: Any aspect of the situation created by the researcher that suggests to participants what behavior is expected.
demographic questions: Questions in a survey or research study about the characteristics of a participant, such as age, marital status, and education level.
demographic variables: Data that describe the participants in a study (e.g., their age, gender, education, etc.). This information should be routinely collected and reported in research.
dependent variable: Variable that is hypothesized to have a relationship with the independent variable.
descriptive statistics: Those statistics or statistical procedures that summarize and/or describe the characteristics of a sample of scores.
design notation: A way of indicating the number of factors and how many levels of each factor there are. For example, a 2 X 4 X 3 design has three factors with the first factor having two levels, the second having four levels, and the third having three levels.
difference score: Difference between scores on the dependent measure at two points in time.
differential level of constraint: Research in which two or more groups defined on the basis of a preexisting variable are compared on a dependent measure.
differential research: Research that involves comparing two or more existing groups on a dependent variable.
diffusion of treatment: Potential confounding variable that occurs when participants in one condition communicate information to participants in another condition. This can be a particular problem in research settings where participants are in close communication with one another, such as in a school or hospital or in the undergraduate psychology subject pool of a university.
direct differences t-test: See correlated t-test.
discrete variable: A discrete variable can take on only a finite number of values. Often contrasted with continuous variable.
discussion section: The final substantive section of a research report, in which the researcher interprets the findings in light of other research and theory.
dispersion: How spread out the scores are in a sample.
diversity: How well various ethnic, cultural, age, and gender groups are represented in the research sample.
double-blind procedure: Research procedure in which neither the researcher nor the participant knows to which condition the participant was assigned. The purpose is to minimize the possibility of experimenter bias and of participant expectancies.