DALYs (disability-adjusted life years) A measure of the reduced quality of life caused by disability.

deductive reasoning Reasoning from a general statement, premise, or principle, through logical steps, to figure out (deduce) specifics. (Also called top-down reasoning.)

deferred imitation A sequence in which an infant first perceives something done by someone else and then performs the same action hours or even days later.

Defining Issues Test (DIT) A series of questions developed by James Rest and designed to assess respondents’ level of moral development by having them rank possible solutions to moral dilemmas.

delay discounting The tendency to undervalue, or downright ignore, future consequences and rewards in favor of more immediate gratification.

demand/withdraw interaction A situation in a romantic relationship wherein one partner wants to address an issue and the other refuses, resulting in opposite reactions—one insistent on talk while the other cuts short the conversation.

demographic shift A shift in the proportions of the populations of various ages.

dendrite A fiber that extends from a neuron and receives electrochemical impulses transmitted from other neurons via their axons.

deoxyribonucleic acid (DNA) The chemical composition of the molecules that contain the genes, which are the chemical instructions for cells to manufacture various proteins.

dependency ratio A calculation of the number of self-sufficient productive adults compared with the number of dependents (children and the elderly) in a given population.

dependent variable In an experiment, the variable that may change as a result of whatever new condition or situation the experimenter adds. In other words, the dependent variable depends on the independent variable.

developmental psychopathology The field that uses insights into typical development to understand and remediate developmental disorders.

developmental theory A group of ideas, assumptions, and generalizations that interpret and illuminate the thousands of observations that have been made about human growth. A developmental theory provides a framework for explaining the patterns and problems of development.

deviancy training Destructive peer support in which one person shows another how to rebel against authority or social norms.

dialectical thought The most advanced cognitive process, characterized by the ability to consider a thesis and its antithesis simultaneously and thus to arrive at a synthesis. Dialectical thought makes possible an ongoing awareness of pros and cons, advantages and disadvantages, possibilities and limitations.

diathesis–stress model The view that psychological disorders, such as schizophrenia, are produced by the interaction of a genetic vulnerability (the diathesis) and stressful environmental factors and life events.

difference-equals-deficit error The mistaken belief that a deviation from some norm is necessarily inferior to behaviors or characteristics that meet the standard.

differential sensitivity The idea that some people are more vulnerable than others are to certain experiences, usually because of genetic differences.

disability Difficulty in performing normal activities of daily life because of some physical, mental, or emotional condition.

disenfranchised grief A situation in which certain people, although they are bereaved, are prevented from mourning publicly by cultural customs or social restrictions.

disengagement theory The view that aging makes a person’s social sphere increasingly narrow, resulting in role relinquishment, withdrawal, and passivity.

disorganized attachment A type of attachment that is marked by an infant’s inconsistent reactions to the caregiver’s departure and return.

distal parenting Caregiving practices that involve remaining distant from the baby, providing toys, food, and face-to-face communication with minimal holding and touching.

dizygotic (DZ) twins Twins who are formed when two separate ova are fertilized by two separate sperm at roughly the same time. (Also called fraternal twins.)

DNR (do not resuscitate) order A written order from a physician (sometimes initiated by a patient’s advance directive or by a health care proxy’s request) that no attempt should be made to revive a patient if he or she suffers cardiac or respiratory arrest.

dominant–recessive pattern The interaction of a heterozygous pair of alleles in such a way that the phenotype reflects one allele (the dominant gene) more than the other (the recessive gene).

double effect A situation in which an action (such as administering opiates) has both a positive effect (relieving a terminally ill person’s pain) and a negative effect (hastening death by suppressing respiration).

doula A woman who helps with the birth process. Traditionally in Latin America, a doula was the only professional who attended childbirth. Now doulas are likely to arrive at the woman’s home during early labor and later work alongside a hospital’s staff.

Down syndrome A condition in which a person has 47 chromosomes instead of the usual 46, with 3 rather than 2 chromosomes at the 21st site. People with Down syndrome typically have distinctive characteristics, including unusual facial features, heart abnormalities, and language difficulties. (Also called trisomy-21.)

drug abuse The ingestion of a drug to the extent that it impairs the user’s biological or psychological well-being.

drug addiction A condition of drug dependence in which the absence of the given drug in the individual’s system produces a drive—physiological, psychological, or both—to ingest more of the drug.

Dual Language Learners (DLLs) Children who develop skills in two languages are dual language learners. Ideally education fosters proficiency in two languages rather than creating a language shift.

dual-process model The notion that two networks exist within the human brain, one for emotional and one for analytical processing of stimuli.

dynamic systems A view of human development as an ongoing, ever-changing interaction between the physical, cognitive, and psychosocial influences. The crucial understanding is that development is never static but is always affected by, and affects, many systems of development.

dyscalculia Unusual difficulty with math, probably originating from a distinct part of the brain.

dyslexia Unusual difficulty with reading; thought to be the result of some neurological underdevelopment.