Developmental researchers study human development across the lifespan using various scientific methods to describe, explain, predict, and intervene in developmental changes. They examine physical, cognitive, and socio-emotional development across multiple levels of environmental influence. Research incorporates longitudinal, cross-sectional, and experimental designs while adhering to strict ethical guidelines to protect participants. The overarching goal is to understand the complex interplay between nature and nurture over time in order to optimize well-being.

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THE RESEARCH METHOD OF HUMAN
DEVELOPMENT
Researching the process of human development across cultures provides us with an opportunity to
improve the human condition as well as, hopefully, to acquire the knowledge needed to optimize life
satisfaction. We therefore begin with an overview of how diverse social science and life science
researchers (collectively known as developmentalists) approach the monumental task of studying
humans over the course of the life span. Our discussion includes the goals of the scientific community,
the recognized framework for studying the life span, what aspects of development warrant extensive
examination, and what scientific methods are used to conduct research with humans. This article also
discusses the main developmental theories over the past 100 years, when social scientists, biologists,
and chemists focused on studying discrete aspects of human development. Earlier introspective
methods about subconscious experience and contemporary measurable evidence about microscopic
genetic codes, neurons, and hormones all contribute to our understanding of the human condition.
Contemporary researchers are focusing on how to integrate scientific findings and theory from across
cultures into a more meaningful whole about human development.
Critical Thinking Questions
1. Developmental change takes place in three fundamental domains: physical, cognitive, and
emotional-social. Which domain has been most important for your becoming who you are? Will
any one of the domains become more important as you get older?
2. Make a list of three aspects of yourself that have changed over the last 10 years and three that
have remained constant. How do you feel about both the “dynamic” and the “static” aspects of
yourself?
3. If someone had researched your personal development over time, where would they have
noticed the most change? The least change? If they continued their research, where would they
probably see the most and least amount of change over the next 10 years, in your opinion?
4. If we could answer most of the important questions about human development by continu-
ously studying 10 individuals who interact with each other from birth until death, would the
knowledge gained from the study justify keeping them isolated from the rest of the world for
their entire lives? Critical Thinking Questions Outline
The Study of Human Development
Scientists refer to the elements of change and constancy over the life span as development.
Development is defined as the orderly and sequential changes that occur with the passage of time as an
organism moves from conception to death. Development occurs through processes that are biologically

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programmed within the organism and processes of interaction with the environment that transform the
organism.
Human development over the life span is a process of becoming something different while remaining in
some respects the same. Perhaps what is uniquely human is that we remain in an unending state of
development. Life is always an un-finished business, and death is its only cessation.
Traditionally life-span development has primarily been the province of psychologists. Most commonly
the field is called developmental psychology or, if focused primarily on children, child development or
child psychology. Psychology itself is often defined as the scientific study of behavior and mental
processes. Developmental psychology is the branch of psychology that deals with how individuals
change with time while remaining in some respects the same. The field of life-span development has
expanded to include not only infant, child, adolescent, and adult psychology but also biology, genetics,
women’s studies, medicine, sociology, gerontology, anthropology, and cross-cultural psychology. A
multi-disciplinary approach stimulates fresh perspectives and advances in knowledge
The Goals of Developmental Psychologists
People actively shape and give direction to their own development (Riediger, Freund, & Baltes, 2005).
Within the context of developmental theory across the life span, scientists focus on four major goals
related to a continuum of optimization of functioning in the early years and com- pensation for losses
with advancing years (Ebner, Freund, & Baltes, 2006):
 To describe changes that typically occur across the life span. Social scientists describe the paths
young adults (ages 18 to 29) take as they move from parental homes. What percent go to work,
enter college or military life, stay single or enter cohabitation or married life, or withdraw into a
subculture or prison?
 To explain these changes—to specify the determinants of developmental change. What factors
impact a young person’s decision to leave home and establish a “new” life? How do peers,
culture, economics, or religious affiliation influence the decision of delay, leave-taking, or return
(Arnett, 2007)?
 To predict developmental changes. What are the expected consequences of delayed leave-
taking or frequent returns to home on the young adult as well as the impact on the parent(s)
and society (Arnett, 2007)? College graduates with high student loans and divorced or single
young adults with children have higher return rates.
 To be able to use their knowledge to intervene in the course of events in order to control them.
Social scientists describe a “boomerang generation” of many in their twenties and older that
leave and return to the support of the parental home—leading to a new stage of life in
industrialized societies called “emerging adulthood” (Arnett, 2007). See the Further
Developments box on page 6, “An In-Between Stage: Emerging Adulthood.”

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But even as scientists strive for knowledge and con- trol, they must continually remind themselves of
the ethical dangers described by eminent physicist J. Robert Oppenheimer (1955): “The acquisition of
knowledge opens up the terrifying prospects of controlling what people do and how they feel.” We
return to the matter of ethical standards in scientific research later in this chap- ter. The four scientific
goals—describing, explaining, predicting, and having the ability to control or manage developmental
changes—should be kept in mind as you examine the different domains and theories of human
development in this book.
A Framework for Studying Development
Developmental change takes place in three fundamental domains: physical development, cognitive
develop- ment, and emotional-social development. Yet each of these factors is intertwined in every
aspect of human development.
The concepts of growth, maturation, and learning are important to our understanding of human
development. The interaction between heredity and environment gives each individual his or her unique
characteristics.
Bronfenbrenner’s ecological approach to development examines the mutual accommodations between
the developing person and four levels of expanding environmental influence from the network of social
relationships and the physical settings in which a person is involved daily; to the overarching cultural
patterns of a society that are expressed in family, educational, economic, political, and religious
institutions.
The passage of time has been treated as synonymous with chronological age, but social and behavioral
scientists have broadened their focus to take into account the changes that occur over time in the
environment—and the dynamic relation between change in the person and change in the environment.
Partitioning the Life Span: Cultural and Historical Perspectives
All societies divide this cycle into age strata that reflect social definitions, but definitions often vary
from one culture to another and from one historical period to another.
Age is a master status, so most changes in roles over a per- son’s life span are accompanied by a change
in chronologi- cal age. Each culture gives distinctive meaning, and assigns social responsibilities, to those
in various life stages.
All societies are organized into age strata, and people’s behavior within various age strata is regulated
by the social norms or specifi c expectations for appropriate and inappropriate behavior.
In the United States, we view the life span in terms of prenatal development, infancy, childhood, ado-
lescence, adulthood, and old age. Some developmen- talists suggest there is a newer stage of emerging

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adulthood, between adolescence and adulthood. Because many Americans are living well into their
eighties and nineties, old age is evolving into young- old and the old-old.
The Nature of Developmental Research
Using the scientifi cmethod, developmental researchers focus on change that occurs over time or with
age. The scientifi c method incorporates these steps: select a researchable problem, formulate a
hypothesis, test that hypothesis, draw conclusions about the hypothesis, and make the findings
available to the scientific community.
In developmental research, three basic designs are used: (a) the longitudinal design, (b) the cross-
sectional design, and (c) the sequential design.
The longitudinal design measures the same individuals at regular intervals between birth and death. It
allows researchers to describe sequential change, but such studies cannot control for unusual events
during the participants’ life span, and they are time-consuming and costly.
The cross-sectional design compares different groups of people of different ages at the same time.
The sequential design involves measuring more than one age cohort over time. Conducting sequential
designs can also be costly and complex.
The experimental design is one of the most rigorously objective techniques available to science. It offers
the only effective technique for establishing cause-and- effect relationships when it is conducted with
precision. Two groups of individuals are compared: the experi- mental group and the control group, and
the scores of these two groups are analyzed for statistically signifi cant differences to determine
whether a causal relationship exists.
The case-study method is a longitudinal study that describes one individual’s experience and behavior
over time and provides rich detail and description, but its fi ndings cannot easily be generalized to other
individuals, other settings, and other time periods.
The social survey method uses questionnaires, inter- views, and surveys to measure attitudes and
behaviors of a sample of people who represent a larger group of the population.
The naturalistic observation method enables a researcher to study people independently of their ability
or willing- ness to report on themselves.
The cross-cultural method allows scientists to specify which theories in human development hold true
for all societies, which hold for only certain types of societies, and which hold for only a particular
society.

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Research Analysis
Correlational analysis quantifies the relationship between two or more variables in terms of strength
and direction but does not prove causation. It can be used for prediction, depending on the strength of
the positive or negative relationship.
Ethical Standards for Human Development Research
A scientist must conduct research with respect for the integrity of the participants and must secure
informed consent, assure participants of their safety, and inform participants that their individual
performance will be kept confidential. The American Psychological Association and the Society for
Research in Child Development have developed strict guidelines that must be followed with research
participants.