A general term for the traits, capacities, and limitations that each individual inherits genetically from his or her parents at the moment of conception.

The science that seeks to understand how and why people of all ages and circumstances change or remain the same over time.

People whose ancestors were born in the same region and who often share a language, culture, and religion.

The repetition of a study, using different participants.

A general term for all the environmental influences that affect development after an individual is conceived.

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

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.

A specific prediction that can be tested.

A way to answer questions that requires empirical research and data-based conclusions.

Evidence that is based on observation, experience, or experiment, not theory.

A time when a certain type of development is most likely to happen or happens most easily, although it may still happen later with more difficulty. For example, early childhood is considered a sensitive period for language learning.

A number that indicates the degree of relationship between two variables, expressed in terms of the likelihood that one variable will (or will not) occur when the other variable does (or does not). A correlation indicates only that two variables are related, not that one variable causes the other to occur.

In an experiment, the variable that is introduced to see what effect it has on the dependent variable. (Also called experimental variable.)

A research method in which the researcher tries to determine the cause-and-effect relationship between two variables by manipulating one (called the independent variable) and then observing and recording the ensuing changes in the other (called the dependent variable).

The view that in the study of human development, the person should be considered in all the contexts and interactions that constitute a life. (Later renamed bioecological theory.)

A research design that compares groups of people who differ in age but are similar in other important characteristics.

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

An in-depth study of one person, usually requiring personal interviews to collect background information and various follow-up discussions, tests, questionnaires, and so on.

A group defined by the shared age of its members, who, because they were born at about the same time, move through life together, experiencing the same historical events and cultural shifts.

A research design in which the same individuals are followed over time and their development is repeatedly assessed.

A hybrid research design in which researchers first study several groups of people of different ages (a cross-sectional approach) and then follow those groups over the years (a longitudinal approach). (Also called cohort-sequential research or time-sequential research.)

A method of testing a hypothesis by unobtrusively watching and recording participants’ behavior in a systematic and objective manner in a natural setting or in a laboratory; a search of archival data is another way to conduct scientific observation.

Referring to the effects of environmental forces on the expression of an individual’s, or a species’, genetic inheritance.

A system of shared beliefs, norms, behaviors, and expectations that persist over time and prescribe social behavior and assumptions.

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.

An approach to the study of human development that takes into account all phases of life, not just childhood or adulthood.

An idea that is based on shared perceptions, not on objective reality. Many age-related terms, such as childhood, adolescence, yuppie, and senior citizen, are social constructions.

A group of people who are regarded by themselves or by others as distinct from other groups on the basis of physical appearance, typically skin color. Social scientists think race is a misleading concept, as biological differences are not signified by outward appearance.

A time when a particular type of developmental growth (in body or behavior) must happen if it is ever going to happen.

A research method in which information is collected from a large number of people by interviews, written questionnaires, or some other means.

A person’s position in society as determined by income, wealth, occupation, education, and place of residence. (Sometimes called social class.)