Editing Developmental psychology (section)

==Research methods and designs==
===Main research methods===
Developmental psychology employs many of the [[psychological research methods|research methods]] used in other areas of psychology. However, infants and children cannot be tested in the same ways as adults, so different methods are often used to study their development.

Developmental psychologists have a number of methods to study changes in individuals over time. Common research methods include systematic observation, including [[naturalistic observation]] or structured observation; self-reports, which could be clinical interviews or [[structured interviews]]; clinical or [[case study]] method; and [[ethnography]] or participant observation.{{sfn|Berk|2012|pp=31–35}} These methods differ in the extent of control researchers impose on study conditions, and how they construct ideas about which variables to study.<ref name=Bruning>{{cite book| vauthors = Moshman D, Glover JA, Bruning RH |title=Developmental psychology : a topical approach|year=1987|publisher=Little, Brown|location=Boston|isbn=978-0-316-58561-3|pages=82–96}}</ref> Every developmental investigation can be characterized in terms of whether its underlying strategy involves the ''experimental'', ''correlational'', or ''case study'' approach.<ref name=Achenbach>{{cite book| vauthors = Achenbach TM |title=Research in development psychology.|year=1978|publisher=Free Pr. [usw.]|location=New York [usw.]|isbn=978-0-02-900180-6|pages=74–104}}</ref><ref name=Prentice-Hall>{{cite book| vauthors = Marmor RM, Liebert R, Wicks P, Gloria S |title=Developmental psychology|year=1977|publisher=Prentice-Hall|location=Englewood Cliffs, N.J.|isbn=978-0-13-208231-0|pages=20–37|edition=2d}}</ref> The [[experimental method]] involves "actual manipulation of various treatments, circumstances, or events to which the participant or subject is exposed;<ref name=Prentice-Hall /> the ''experimental design'' points to [[Causality|cause-and-effect relationships]].<ref name=Shaffer>{{cite book| vauthors = Shaffer DR |title=Social and personality development|year=2009|publisher=Wadsworth|location=Australia|isbn=978-0-495-60038-1|pages=21–36|edition=6th}}</ref> This method allows for strong inferences to be made of causal relationships between the manipulation of one or more [[independent variables]] and subsequent behavior, as measured by the [[dependent variable]].<ref name=Prentice-Hall /> The advantage of using this research method is that it permits determination of cause-and-effect relationships among variables.<ref name=Shaffer /> On the other hand, the limitation is that data obtained in an artificial environment may lack generalizability.<ref name=Shaffer /> The correlational method explores the relationship between two or more events by gathering information about these variables without researcher intervention.<ref name=Prentice-Hall /><ref name=Shaffer /> The advantage of using a correlational design is that it estimates the strength and direction of relationships among variables in the natural environment;<ref name=Shaffer /> however, the limitation is that it does not permit determination of cause-and-effect relationships among variables.<ref name=Shaffer /> The [[case study]] approach allows investigations to obtain an in-depth understanding of an individual participant by collecting data based on [[interviews]], structured questionnaires, observations, and test scores.<ref name=Shaffer /> Each of these methods have its strengths and weaknesses but the experimental method when appropriate is the preferred method of developmental scientists because it provides a controlled situation and conclusions to be drawn about cause-and-effect relationships.<ref name=Prentice-Hall />

===Research designs===
Most developmental studies, regardless of whether they employ the experimental, correlational, or case study method, can also be constructed using research designs.<ref name=Bruning /> Research designs are logical frameworks used to make key comparisons within research studies such as:
* [[cross-sectional design]]
* [[longitudinal design]]
* [[cohort study|sequential design]]
* [[microgenetic design]]

In a [[longitudinal study]], a researcher observes many individuals born at or around the same time (a [[cohort (statistics)|cohort]]) and carries out new observations as members of the cohort age. This method can be used to draw conclusions about which types of development are universal (or [[norm (sociology)|normative]]) and occur in most members of a cohort. As an example a longitudinal study of early literacy development examined in detail the early literacy experiences of one child in each of 30 families.<ref>{{cite thesis |last1=Worthington |first1=John |date=2001 |title=A longitudinal study of early literacy development and the changing perceptions of parents and teachers |doi=10.14264/105711 }}{{pn|date=January 2025}}</ref>

Researchers may also observe ways that development varies between individuals, and hypothesize about the causes of variation in their data. Longitudinal studies often require large amounts of time and funding, making them unfeasible in some situations. Also, because members of a cohort all experience historical events unique to their generation, apparently normative developmental trends may, in fact, be universal only to their cohort.{{sfn|Berk|2012|p=40}}

In a [[cross-sectional study]], a researcher observes differences between individuals of different ages at the same time. This generally requires fewer resources than the longitudinal method, and because the individuals come from different cohorts, shared historical events are not so much of a [[lurking variable|confounding factor]]. By the same token, however, cross-sectional research may not be the most effective way to study differences between participants, as these differences may result not from their different ages but from their exposure to ''different'' historical events.{{sfn|Berk|2012|p=41}}

A third study design, the [[cohort study|sequential design]], combines both methodologies. Here, a researcher observes members of different birth cohorts at the same time, and then tracks all participants over time, charting changes in the groups. While much more resource-intensive, the format aids in a clearer distinction between what changes can be attributed to an individual or historical environment from those that are truly universal.{{sfn|Berk|2012|p=42}}

Because every method has some weaknesses, developmental psychologists rarely rely on one study or even one method to reach conclusions by finding consistent evidence from as many converging sources as possible.<ref name=Prentice-Hall />