Toward Enhancing the Role of Idiographic-Based Analyses in Describing, Explaining, and Optimizing the Study of Human Development: The Sample Case of Adolescent ⇔ Family Relationships

The Sample Case of AdolescentO Family Relationships

Richard M. Lerner, Jacqueline V. Lerner; and Paul A. Chase

Since the founding of scientific psychology in 1879, with the opening of Wilhelm Wundts Leipzig, Germany, laboratory (Boring, 1950; Danziger, 1990; Misiak & Sexton, 1966) and continuing through the early decades of the 20th century (e.g., Allport, 1937; Kluckhohn & Murray, 1948), a focus on the individual and on changes within the individual as a consequence of experimentally or ontogenetically based variation was of key empirical interest. Whereas concern for generalizations across individuals, or about variables in contrast to people, were and still remain a vital part of the study of human behavior and development, the early decades of psychological science included a robust interest in phenomena or “laws” that were person- specific (or idiographic) as well as in phenomena or “laws” that applied to all people (i.e., nomothetic phenomena) or to specific groups of people (i.e., differential phenomena) (e.g., Allport, 1937; Danziger, 1990; Lerner, 2018).

Indeed, Allport (1937) emphasized person specificity (idiography) in founding what he termed a morphogenic approach to personality, an approach to integrate the idiographic with the nomothetic in understanding the uniqueness of each individual. In 1948, reflecting what was by then an almost 70-year tradition, Kluckhohn and Murray observed that each person is like every other person (there are nomothetic features of every persons structure and function), each person is like only some other people (there are subgroup, or differential, features of structure and function pertinent to each individual; Emmerich, 1968), and each person is like no other person (there are idiographic features of structure and function in each individual). A comprehensive and integrated (Overton, 2015) approach to human development should include all three types of information.

In essence, Kluckhohn and Murray suggested that, in some respects, every human possesses universal or nomothetic characteristics, that is, characteristics of all humans by virtue of membership in the human species. For example, all humans have respiratory, circulatory, nervous, and digestive systems. Each human also possesses characteristics that place him or her in specific groups; that is, each person has differential characteristics. For example, the reproductive systems of males and females are different. Moreover, the intersection of such attributes as race, ethnicity, religion, socioeconomic status, and rural versus urban area of residence may further place people into subgroups useful for addressing specific questions about human development (Bornstein, 2017). Finally, every human has characteristics that are specific to him or her; there are idiographic characteristics. For example, no two humans, even monozygotic twins, have the same complement of nuclear and mitochondrial DNA (Joseph, 2015; Richardson, 2017) or the same history of experiences across their lives.

All humans have all three types of attributes, and as such, a comprehensive approach to understanding human behavior and development must understand the development and functioning of each type of attribute as well as their dynamic integration across the life span (Overton, 2015). In addition, contemporary theories of human development emphasize that the ecology of human development also has components that are nomothetic, differential, and idiographic (e.g., Bronfenbrenner & Morris, 2006). As such, both individuals (e.g., adolescents) and features of their context (e.g., families) have to be conceptualized as having relations among idiographic, differential, and nomothetic features. Creating models of the dynamic coactions among these components has been and remains a key focus of contemporary theories of human development (Lerner, 2018; Overton, 2015; Overton & Molenaar, 2015).

Scholarship about the structure and function of each type of individual or ecological attribute is needed in the study of human behavior and development—as is scholarship about the coactions among idiographic, differential, and nomothetic features of individual—context relations, especially the mutually influential instances of these relations (represented as individual^context relations) involved in systematic dynamics of human development (Overton, 2015). Flowever, the focus of the present article is on summarizing contemporary ideas and methods associated with studying the idiographic components of the dynamic developmental system (for fuller discussions, see, e.g., Lerner, 2018, Molenaar & Nesselroade, 2012, 2014, 2015; Ram & Grimm, 2015; Rose, 2016; von Eye, Bergman, &: Hsieh, 2015). We choose this emphasis as a result of our observation that interest in at least quantitative approaches to the idiographic components of human development has diminished from the levels of scholarly focus between 1879 and the late 1940s (see, e.g.. Rose, 2016).

This change may be a result of the relative absence of rigorous quantitative methods useful for understanding the role of person-specific variation within the integrated (nomothetic-differential-idiographic) system (Molenaar 8c Nesselroade, 2012, 2014, 2015; Rose, 2016), although of course rigorous qualitative methods that focused on person-specific pathways of development have been present and are flourishing in the study of human development (e.g., Damon & Colby, 2015; Tolan & Deutsch, 2015). We believe that quantitative approaches are flourishing as well (e.g., Molenaar, Lerner, & Newell, 2014), which is why we focus on them in this article. Although our discussion can be applied to any portion of the life span or to any substantive focus of individual or ecological study, we use the study of adolescents and the relationships between adolescents and their families as a sample case.

Indeed, it is possible to extend the points made by Kluckhohn and Murray (1948) to families. There are nomothetic features of families. For instance, all families have a life cycle from initial family formation to the death of the partners who formed the family (e.g., McGoldrick 8c Shibusawa, 2012). In addition, families have group-differential characteristics, such as attributes that are moderated by the specific cultural practices pertinent to each family (e.g., Carter & McGoldrick, 1988; Mistry & Dutta, 2015). Finally, all families have idiographic attributes, ones constituted by the specific individual attributes of the family members who coact across the family life cycle and by the influence of variables associated with the specific historical span in which the family lives. These idiographic attributes also involve specific features of the place (e.g., community, physical ecology) where the family is located at a specific time in history (Elder, 1998; Lerner 8c Chase, 2019; Lerner, Johnson, & Buckingham, 2015a).

Given the unique constellation of nomothetic, differential, and idiographic attributes that defines each family, it is likely that the relationships adolescents have with their families may have also have features that are nomothetic, differential, and idiographic. For instance, all families have to address issues of changing coactions that accompany puberty and the emergence of sexual motivations among adolescent children (Diamond & Savin-Williams, 2009; Susman & Dorn, 2009). Flowever, the changing coactions that accompany puberty and sexual motivation will vary in relation to both the adolescent’s gender and cultural practices regarding sexuality and reproduction (e.g., Diamond 8c Savin-Williams, 2009; Rogoff, 2003). In addition, coactions will vary idiographically—for instance, in relation to parents’ beliefs and values and prevailing historically shaped norms, as well as in relation to an adolescent’s sexual preference or orientation. Similarly, these family coactions will vary by gender and other features of an adolescent’s identity (e.g., race, religion, vocational or career aspirations; Cote, 2009).

Accordingly, it is important to study in an integrated manner nomothetic, differential, and especially idiographic domains of relationship attributes in families with adolescent children—or, in fact, with children of any age (Lerner, 2018; Lerner & Spanier, 1978). Indeed, we suggest the usefulness of beginning efforts to describe, explain, or optimize the relationships between adolescents and their families with a focus on the specific, idiographic attributes of youth and families involved in these relationships (Lerner & Lerner, 2019a, 2019b).

Brief History of Studying the Development of Adolescent—Family Relationships

The study of relationships between adolescents and their families has a long theoretical and empirical history, arguably beginning in the behavioral and social sciences with Hall’s (1904) recapitulationist conception of adolescence as marked by storm and stress—phenomena that were presumably associated at least in part with problematic or negatively valenced relationships with parents. Although few developmental scientists adhered to Hall’s (1904) ideas about ontogeny recapitulating phylogeny, many scholars proposed other biological reductionist concepts (e.g., Anthony, 1969; Erikson, 1950, 1959, 1968; Freud, 1969) that explicitly pointed to the universal and inevitable conflicts between adolescents and parents.

However, as research about adolescence in general burgeoned during the middle decades of the 20th century (e.g., Bandura, 1964; Elder, 1974), and as research about adolescent—family relationships more specifically, began to emerge (e.g., Douvan 8c Adelson, 1966; Offer, 1969), findings did not support either the universality of general storm and stress during adolescence or, more specifically, the universality of problematic adolescent—family relationships. For instance, Offer (1969) reported that most young people do not experience a stormy adolescent period. Moreover, Douvan and Adelson (1966) found that, although adolescents spent increasingly more time with peers than with parents, most adolescents were shown to still place enormous value on their relationships with parents. Douvan and Adelson’s research showed that most adolescents had core values (e.g., importance of education, social justice, spirituality) consistent with those of their parents. Indeed, most adolescents selected friends who shared these core values.

As Elder (1980) explained, the context of adolescent and family life— most notably the specific time (ontogenetic, family or generational, and historical) and the specific place (e.g., rural vs. urban; Elder, 1998; Elder, Modell, & Parke, 1993; Elder, Shanahan, & Jennings, 2015) of adolescent- family relationships—mattered most in describing and explaining the specific attributes (e.g., the positive-to-negative valences of youth—parent coactions) associated with adolescent—family relationships. As such, the data accumulated over the course of the mid- to late 20th century (for reviews, see, e.g., Lerner & Steinberg, 2009) indicated that biological (or, more specifically, genetic) reductionist accounts of adolescent development or adolescent—family relations could not explain the course of change either in youth development or in adolescent—family relationships (e.g., Lerner, 2018). Because time and place moderated the course of these relationships, data from the study of adolescent development suggested that explanations other than reductionist ones are needed to account for how youth and families developed the specific relationships that marked their lives (e.g., Born- stein, 2017).

As such, models involving the coactions of a young person and his or her family as well as coactions of adolescent and family with the broader ecological setting (e.g., community, culture, historical era) emerged to frame descriptive and explanatory scholarship (e.g., Bronfenbrenner, 1979, 2005; Bronfenbrenner & Morris, 2006; Lerner, 1978, 2004; Lerner & Spanier, 1978; see also Lerner & Steinberg, 2009). This work was both a product and a producer of the Zeitgeist of developmental theory in the latter decades of the 20th century—a conceptual emphasis on dynamic relational developmental systems—based models. This emphasis has continued through the first two decades of the 21st century (e.g., Lerner, 2015, 2018; Overton, 2015).

More than conceiving of adolescents and their families as distinct entities that interrelate analogously to terms in the statistical interactions of analyses of variance or multiple regression, these dynamic models focus on fused or integrated relations (Lerner & Overton, 2017). As such, bidirectional relations between individuals and their contexts (represented as individualOcontext relations) and bidirectional and mutually influential relationships between adolescents and families (i.e., adolescent О family relationships) were regarded as the fundamental unit of analysis in descriptive and explanatory research. In addition, these relational developmental systems-based models (e.g., the Positive Youth Development model used by Lerner, Lerner, Bowers, & Geldhof, 2015) have important implications for the optimization of adolescent<=> family relationships.

These implications are different from those associated with models that focus on either nomothetic or differential facets of the relationships adolescents have with their families and, especially, from nomothetic or differential models that use genetic reductionism to explain adolescent-family relationships (e.g., Belsky, Steinberg, & Draper, 1991; Bjorklund & Ellis, 2005; Del Giudice, 2014; Figueredo et al., 2006). To understand these theory-based differences, we briefly discuss the key concepts associated with the relational developmental systems (RDS) metatheory.

The Relational Developmental Systems Metatheory:

An Overview

The study of human development has evolved from a field dominated by reductionist (psychogenic or biogenic) approaches to a multidisciplinary scholarly domain that seeks to integrate variables related to biology', culture, and historical levels of organization across the life span into a synthetic, coactional system (e.g., Elder, 1998; Ford & Lerner, 1992; Gottlieb, 1998; Lerner, 2018; Lerner & Lerner, 2019a, 2019b). This approach to human development contrasts with all reductionist accounts of change across the life span, which in the main have been shaped by the philosophical ideas of Rene Descartes (Overton, 2013). Cartesian conceptions split reality into purported fundamental or essential phenomena and derivative or secondary phenomena (Overton, 2015). For researchers, reductionist views in social and behavioral science elevated the salience of such split formulations as nature versus nurture, continuity versus discontinuity, stability versus instability, or basic versus applied science (Lerner, 2002, 2006).

Across the past four decades, several scholars have contributed to the evolution of this RDS metatheory (e.g., Bakes, 1997; Brandtstiidter, 1998; Bronfenbrenner, 1979, 2005; Bronfenbrenner & Morris, 2006; Elder, 1998; Elder et al., 2015; Ford & Lerner, 1992; Nesselroade, 1988; Over- ton, 1973; Overton & Reese, 1981; Riegel, 1976; von Bertalanffy, 1933). However, Overton (2015) has been key to integrating and extending this scholarship.

Overton (2015) explained that, in comparison with a Cartesian worldview involving splits, reductionism, essentialism, positivism, and mechanism, RDS metatheory is associated with a superordinate process—relational paradigm. The ideas in this paradigm focus on process (systematic changes in the developmental system), becoming (moving from potential to actuality; a developmental process with a past, present, and future; Whitehead, 1929/1978), holism (the meanings of entities and events derive from the context in which they are embedded), relational analysis (assessment of mutually influential relations in the developmental system), and the use of multiple perspectives and explanatory forms (ideas from multiple theory- based models of change within and of the developmental system). In the process—relational paradigm, the organism is seen as inherently active, self- creating, self-organizing (autopoietic), self-regulating (agentic), nonlinear and complex, adaptive, and at least relatively plastic—that is, it possesses the potential for systematic change through dynamic coactions with the context (Overton, 2015).

Theoretical models derived from this paradigm emphasize such plasticity (Lerner, 2018), and that development across life involves mutually influential relations in a dynamic system. This idea frames RDS metatheory. Split conceptions are obviously eschewed in favor of a metatheory that emphasizes the study and integration of different levels of organization, including biology, physiology, culture, physical ecology, and history, as a means to understand human development over the life span (Lerner, 2018; Over- ton, 2015). Accordingly, the conceptual emphasis in RDS theories is placed on mutually influential relations between individuals and contexts. In this regard, we recognize that the representation of the dynamic relations among variables, both within and across levels of organization within the ecology of human development, cannot be fully represented by the bidirectional arrow (<=>) between individual and context that we have presented in this article. However, other representations of the dynamic, relational developmental system (e.g., Lerner, 2018; Lerner, Johnson, & Buckingham, 2015a) are too complex or cumbersome to use in a narrative discussion of these dynamic relations; as such, we believe the individualOcontext relation representation suffices.

In any case, in the context of such a bidirectional relational system, the embeddedness within history (temporality) is of fundamental significance (Elder, 1998; Elder et al., 2015). Simply put, the developmental system is embedded in history (temporality). One implication of this embeddedness is that individuals born at the time of our writing this article will have paths through life that are different in substance, events, and outcomes from those of their grandparents and parents and, in turn, different from those of their future children and grandchildren. Time and place are fundamental moderators—and in this case, regulators—of the life course and of the substance, pace, direction, and outcome of the development of individuals, families, or other groups, and even communities or macrosocietal organizations (e.g., political organizations, educational systems, faith communities). Moreover, this contextual moderation ensures that development at each level of organization has systematic, individual, or idiographic components, as well as nomothetic and differential components (Emmerich, 1968; Kluckhohn &: Murray, 1948).

Nomothetic, Differential, and Idiographic Features of Adolescents and Families

Similar to individuals, families also have nomothetic, differential, and idiographic features. Whereas a full discussion of these domains of attributes is beyond the purposes of this article, it is useful to again refer to the family life-cycle literature (e.g., Carter & McGoldrick, 1988; Loomis, 1936; McGoldrick & Shibusawa, 2012; Spanier, Lewis, & Cole, 1975; Spanier, Sauer, & Larzelere, 1979) to illustrate this point. All families have a life cycle, and thus there is universal applicability of the concept of changes in family structure over a developmental course, beginning with the initiation of a new family. However, there is not one form of the family life cycle. The structure, function (e.g., changes in marital quality; Spanier et al., 1979), and life course events of families differ according to the intersection of, for instance, cultural, socioeconomic, and geographic variables (Lerner, 2018; Lerner & Spanier, 1978). Moreover, this group-level variation is complicated by variation particular to each family—for example, the intersection of age, gender, race, religion, values, and parenting style of the parent or parents, as well as age, developmental attributes, gender, and other psychological and demographic characteristics of children (Gore & Gore, 2002). As such, the coactions between children or adolescents and the other members of their family will also vary idiographically in relation to the moderating effects of the other variables (Lerner, 2004, 2018).

These instances of individual and family variation are well known, and as such, there is no theoretical or empirical controversy over the fact that each person or family possesses nomothetic, differential, and idiographic characteristics (Kluckhohn & Murray, 1948). However, there are differences in developmental scientists’ preferences or values when deciding which, if any, of these domains of characteristics they should emphasize in their conceptualizations and empirical elucidations of development within and across periods of life. Developmental science has a long history of focusing on theories that emphasize the generic, or nomothetic, facets of human development, for instance, as instantiated by an interest in universal stage theories of development (e.g., Erikson, 1959; Freud, 1969; Kohlberg, 1978; Piaget, 1970). These theories reflect minimal interest in individual differences, whether at the level of group differences or at the level of idiographic characteristics (Lerner, 2018).

Similarly, some researchers assessing adolescent development have focused on differential patterns ofyouth development (e.g., Blocks 1971 classic study, Lives Through Time). However, as with stage theorists, in Blocks book the nature of individual differences in youth development was restricted to the several clusters of groups or subgroups into which people could be sorted within and across time. Block (1971) differentiated males from females, and he indicated that adolescent and young adult males could be differentiated into five subgroups, whereas adolescent and young adult females could be differentiated into six subgroups.

However, scholars involved in differential research about adolescents make differentiations in addition to age level and gender (e.g., Ganong, Coleman, & Russell, 2015; Lamb, 2015; Murry, Hill, Witherspoon, Berkel, & Bartz, 2015), including race, religion, ethnicity, socioeconomic status, place of residence (e.g., rural, urban, suburban), family type, and cultural context. The intersection of these different instances of diversity provide a means for researchers using a differential approach to human development in general or to adolescence more specifically, to specify and study quite diverse subgroups within a larger population of young people.

In contrast to the theoretical and empirical scholarship about nomothetic and differential patterns of development that have marked, and continue to mark, the adolescent development literature, to our knowledge there has been no quantitative-based theoretical model offered in developmental science about the person-specific idiographic patterns of adolescent development, family development, or the development of adolescent<=> family relationships (although qualitative, case-study methods have provided such information in regard to, for example, facets of character development; Damon & Colby, 2015). The quantitative methodology of developmental science has focused more on the study of groups (either universal or group-differential ones) than on the idiography of human development. However, Molenaar and Nessel- roade (2014, 2015) and Rose (2016) have pointed to the shortcomings of a focus that excludes consideration of idiographic change.

As Rose, Rouhani, and Fischer (2013) have explained, individual^context relations are the fundamental process of living organisms. As such, to understand and fruitfully empirically examine the course of individual development, researchers must use two concepts integral to dynamic systems models—individual-in-context and variability across individuals and across individual—context relations—and they should consider these concepts pertinent to substantive information about development, not error variance (Rose et ah, 2013):

Behavior is not something that a person ‘has’—instead, it emerges from interactions between the individual and his or her contexts. . . . [The] dynamic systems approach starts by assuming individuals vary, and seeks to identify stable patterns within that variability.

(p. 153)

There are important implications for theory and research if a researcher begins a scientific study of individuals, families, or adolescent <=> family relationships by focusing first on individual-level variability. These implications arise because of dynamic developmental systems models’ focus on the specificity of individual<=>context relations and the idiographic features of human development (Rose et al., 2013). These ideas provide a rationale for a distinct approach to diversity', one with implications for the description, explanation, and optimization of human development in general and of adolescent О family relationships more specifically'.

To explore these implications, it is important to introduce the specificity principle (Bornstein, 2017). Through this principle, developmental scientists ask multipart “what” questions when exploring the function, structure, and content of development of individuals or families across the life span. For instance, in seeking to understand how diverse youth may have a specific series of individual^family relationships associated with adaptive, healthy, or positive development, researchers might undertake programs of research framed by' a multipart question such as the following: What specific features of positive individual and family development emerge? Linked to what specific trajectory of individualOfamily relationships? For youth and other family members possessing what specific sets of individual psychological, behavioral, and demographic characteristics? Living in what specific neighborhoods, physical ecological conditions, nations, and cultures? At what specific points in ontogenetic and generational time? Within what specific historical periods?

Through conducting programmatic research addressing such questions, the specific sets of adolescent<=>family relationships involved in a person’s life can be identified (e.g.. Elder et al., 2015) and the specific relations associated with individual and family positive development can be discovered (e.g., Rose, 2016). Therefore, a key outcome of such research framed by the specificity' principle can be the identification of the diverse ways in which adolescent О family relationships may capitalize on the potential for plasticity in human life and result in adaptive, healthy, or positive development of these relationships (Spencer, Swanson, & Harpalani, 2015). However, this outcome—that is, moving beyond description and explanation to optimization of developmental change—requires a developmental approach to the measurement of adolescent О family relationships.

A Developmental Approach to Measuring Development of the Adolescent<=>Family Relationship

Whether the “unit of analysis” is an individual, family, or adolescent О family relationship, human development involves systematic, organized, and successive changes within a specific unit across the life span (Lerner, 2018). This fundamental—and obvious—point is not controversial among developmental scientists. All researchers who study development would agree that they want to understand (a) how best to describe changes within a unit of analysis; (b) how to explain what specific changes occur at specific times in life for specific units of analysis living in specific contexts; and (c) how to optimize the changes for each unit of analysis so that the probability of health and positive development will characterize the life pathway.

Given unanimity on the definition of development as systematic change within a unit of analysis, and also the three goals of studying development, it might seem obvious that researchers studying development should use or seek to create measures able to detect within-unit changes. However, across the history of the study of human development, such measurement has not been undertaken invariantly. Across the history of the study of human development, most measures used to study development have not been measures of within-person change!

It may surprise people not schooled in the history of measurement in the study of human development to learn that researchers in the field have devoted more effort to studying changes in variables than in people. For instance, researchers have studied changes in such individual variables as selfregulation, executive functioning, or growth mind-set; such family variables as marital quality' (across the family life cycle; McGoldrick & Shibusawa, 2012; Spanier et al., 1979), and such adolescent<=>family relationship variables as positive or negative valence of social exchanges or time spent together or separately. Researchers in the field of human development have amassed a great deal of knowledge about how to measure such variables with reliability' and validity, and these researchers know whether scores for variables stay the same or change across points in the life span. Unfortunately, however, this information is not necessarily relevant to describing, explaining, or optimizing the development of any specific unit of analysis. Why?

The Three Essential Parts of All Measures of Development

Whenever a researcher sets out to measure any facet of human development, he or she combines (a) a measure of a specific variable (e.g., selfregulation, marital quality, quality' of social exchange between an adolescent and parents), for (b) a specific unit of analysis at (c) a specific measurement time point. That is, the measurement always involves a “score” for a specific variable, for a specific unit, and for a specific measurement time. Say that 100 units (e.g., individuals, marriages, pairs of adolescents and parents) are involved in a study of development and three measurement times are involved in the research design. In this case, developmental changes could be investigated by assessing the pattern of change for each of the 100 units across the three testing times. Starting with these assessments of each individual unit, researchers could then determine whether they can aggregate individuals by asking, “Are there groups of individuals who change in the same or similar ways?” Thus, starting with the study of within-unit change—that is, the study of development for each unit in the sample—researchers can determine whether more general statements about development are possible.

However, the vast majority of human development studies do not undertake this within-individual approach of first assessing individual development and then determining whether aggregation is possible. The vast majority of studies instead proceed by first aggregating data across individual units. As noted by Rose et al. (2013):

By analyzing statistical averages, not individuals, these models provide descriptions about global regularities in everything from cancer. ... to cognition. . . . However, we argue that the value of such models ultimately depends on whether they apply to individuals; after all, a science of the group is a poor substitute for a true science of the individual. Traditional models often assume that insights about the population automatically apply to all individuals. . . . This assumption is simple, it is understandable, and it is necessary to justify the use of averages to understand individuals. However, it is also wrong!

(p. 152)

Returning to our example, researchers taking the aggregate-first approach would describe the average score for, say, self-regulation, marital quality', or valence of the adolescent О parent relationship at the first measurement time. To compute averages, researchers would sum the scores for each variable and divide by 100 to determine the mean score. Researchers would then compute averages in the same way for data from the second and third measurements. In addition, researchers might assess (e.g., through statistics such as repeated measures analyses of variance) whether a variables means changed across the three times of measurement.

To conduct these analyses, researchers need to have assessed how variables go together across individual units, both within each time of measurement and—because researchers are interested in studying development—across times of measurement. However, what they have learned is how the mean level of a variable—not any one person in the sample—may change or not. Even if the same 100 units were present at each of the three times of testing (if there was no sample attrition across the three testing times), individual units were used only to contribute to the computation of group averages. Researchers in this case may have learned about changes in variables, but they have learned nothing about how variables change within a unit of analysis across life—they have learned nothing about human development. Using average scores for a group obscures multiple pathways and unique contextual influences.

Indeed, as Rose (2016) explained, researchers do not know if or how the information they obtain about variables applies to any of the 100 people in the sample. In other words, aggregation across individual units (as is done when focusing on group statistics) runs the risk of failing to measure or misrepresenting the measurement of developmental change.

Of course, researchers who focus on variables and not on people know that development involves change within a unit of analysis. Why has it remained the case, then, that most developmental research has remained variable focused and not individual focused? Why do researchers studying development continue to focus first on aggregation? Answers here fall into two categories.

First, some researchers claim that variable-centered analyses are good- enough approximations of what would be learned from truly idiographic analyses of a unit. However, such equivalence may not always be the case; in fact, across the present authors’ collective understanding of the literature of human development, there are few identified instances of such equivalence (Molenaar & Nesselroade, 2014, 2015). In fact, almost no evidence exists in published research for the presence of such approximations. In turn, there are scores of examples that, when researchers test the “good enough approximation” assumption, the tests fail (Molenaar & Nesselroade, 2012, 2014, 2015; Rose, 2016).

Nevertheless, a refined version of the good-enough claim has been suggested; close-enough approximations. Some researchers also argue that compromise analyses (e.g., latent trajectory analyses, growth mixture modeling) are good-enough approximations of within-unit analyses, in that they demonstrate that unit subgroups (e.g., of individuals, marriages, relationship types) possess different pathways of development. Again, this argument fails because there is no demonstration that the units in these trajectories all follow similar within-person pathways.

Another reason variable-centered analyses continue to be used despite their shortcomings is that some researchers assert that developmental science is about the general case of humanity (i.e., about what is true across people) and not about an individual instance of an observation—even if the individual is studied across, say, dozens or more observation (time) points (e.g., Ram et al., 2005). The argument is that there is nothing generalizable that can be learned about human development from studying one person or even many people one by one. This idea derives from the belief that science is about what is uniform and permanent across time and context. This assertion, though, is redolent of a philosophical model that has been rejected in contemporary developmental science and has been replaced by dynamic systems conceptions of science that regard the world as differentiated and changing across time and place (Elder et al., 1993; Elder et al., 2015; Lerner, 2018; Overton, 2015). More specifically, it is particularly odd that such assertions of uniformity and permanence would be made by researchers studying development: The study of development is about systematic change, and people change biologically, psychologically, behaviorally, and socially across the life span (Molenaar & Nesselroade, 2015).

Unfortunately, this argument for a focus on generalizations across people is associated with two approaches to measurement that are as flawed as the argument itself, at least insofar as studying development is concerned. The first measurement flaw is based on the erroneous idea that, if uniformity and constancy are the rule, then measures must be developed to reflect this constancy. Indeed, evidence that a measure is detecting change—that it is change sensitive—may be considered direct proof that the measure is poor. In other words, the argument for not measuring within-person change leads to the development of measures that are designed to be change-insensitive across people, time, and contexts. Researchers assuming the good-enough approximation then use such measures to study development and, lo and behold, find no evidence for change (e.g., Costa & McCrae, 1980)! With such evidence, these researchers believe they have proved that the good- enough approximation is warranted.

The second measurement flaw occurs in relation to using such change- insensitive measures. Data analysis is used to document that the use of variable- centered analyses and a focus on averages is justified. These data-analytic procedures are directed toward assessing characteristics of populations, not individuals within that population. The statistics are rationalized mathematically (based on reliance on the ergodic theorems; Molenaar & Nesselroade, 2014, 2015) under the assumptions that all people are homogeneous and their homogeneity is stationary; that is, people remain the same across time and place. However, Molenaar and Nesselroade have documented that the ergodic theorems do not apply to changes within individuals or other units of analysis (e.g., monozygotic twins) studied developmentally. They have demonstrated that development is non-ergodic.

Molenaar and Nesselroade (2014, 2015) have also demonstrated that starting developmental analysis by a focus on the specific, idiographic trajectories of a person (or other unit of analysis) does not preclude aggregation to more molar (differential or nomothetic) levels, if or when such aggregation is empirically warranted (Rose, 2016), that is, when a structural model for such aggregation can be supported empirically. Molenaar and Nesselroade have developed statistical tools that enable researchers to identify more general developmental phenomena even when starting analysis at the idiographic level. For instance, their “idiographic filter” involves

testing whether or not the same latent dynamics (concurrent and lagged factor interrelations) can describe different individuals’ observed multivariate time series. The methodology' allows fitting, across different individuals, dynamic factor models that are invariant with respect to the latent dynamics, but not necessarily the factor loadings (measurement model). This methodology allows the same latent process to manifest differently from one individual to another, thus recognizing that the process is general but its realization in a given person is to some degree idiosyncratic.

(Molenaar & Nesselroade, 2012, p. 2010)

In short, the idiographic filter recognizes “that the way in which a given factor manifests itself in observed variables can be subject-specific" (Molenaar & Nesselroade, 2015, p. 666).

In sum, if the study of human development is to be a science that measures human development, then measures and statistical analyses of data derived from them must be able to detect and analyze systematic change within an analytic unit and also group and nomothetic regularities (i.e., we can return to the observation of Kluckhohn & Murray, 1948, that a comprehensive understanding of human development must include information about all these facets of development). However, focusing on variables and group analyses of scores from change-insensitive measures provides no information about any individual unit’s specific pathways of unit-specific (idiographic) change across life. As a consequence, such an approach to developmental analysis will fail. In particular, this approach will be unable to adequately describe, explain, or optimize the developmental path of an individual youth, a family, or the adolescentOfamily relationship.

Implications of an Idiographic-Based Approach for Optimizing Adolescent<=>Family Relationships

A developmental approach to the study of the adolescent<=> family relationship may usefully start with the assessment of an individual unit of analysis and, as we have explained, aggregate individual data to depict a group only if empirically warranted (Rose, 2016; Rose et al., 2013), such as through use of the idiographic filter (e.g., Molenaar & Nesselroade, 2012). The utility of addressing the optimization goal of developmental science by beginning developmental analysis with a focus on the specificity of the adolescentOfamily relationship may be illustrated by reference to the views of Shonkoff and his colleagues at the Harvard University Center on the Developing Child (Center on the Developing Child, 2017). In “Building a System for Science-Based R&D That Achieves Breakthrough Outcomes at Scale for Young Children Facing Adversity,” Shonkoff and his colleagues asked how their approach to early childhood research and development is different from current best practices. Reflecting the non-ergodic and idiographic approach involved in the Bornstein (2017) specificity principle, they write:

The conventional definition of an “evidence-based” program is met by a statistically significant difference on average between a measured outcome in a group that received an intervention (which typically includes multiple components that are not defined precisely) and that same outcome assessed in a control or comparison group. Frontiers of Innovation challenges this approach. We believe that assessing program effects on average misses what may work exceptionally well for some and poorly (or not at all) for others. Moreover, attempting to create a single “did it work?” test for a multifaceted intervention obscures its active ingredients, leaving only a “black box” that must be adopted in its entirety. We pose a new set of questions, whose answers require a higher level of precision in program design, implementation, and measurement:

  • • What about the program works? If we understand the active ingredients, we are better able to replicate and scale them.
  • • How does it work? Being specific about the underlying mechanisms can help us increase the impacts and assure they will be sustained when we transport the program to other contexts.
  • • For whom does it work and for whom does it not work? When we know more about who is and isn’t responding, we can scale what works for the former and make changes for the latter.
  • • Where does it work? If we specify and understand the relevant contextual factors, then we are better able to make adaptations so it will also work in a multitude of diverse settings.
  • (Center on the Developing Child, 2017, p. 4)

Accordingly, by conducting programmatic research addressing such specificity-based questions, the particular ontogenetic sets of individuals context relations involved in a person’s life can be identified and the specific relations associated with his or her positive development may be discovered (e.g., Rose, 2016)). In essence, specificity principle—framed research focusing on the diversity of human development may be able to identify the specific individuals context relations linked to positive development for specific individuals or groups of individuals.

If so, developmental scientists could capitalize on the relative plasticity of human development (Lerner, 2018; Overton, 2015) and assess whether, by creating conditions for such relations among other, similar individuals, more general positive development could be promoted. The key idea here is that developmental scientists can usefully forgo beginning their developmental study with the overall (nomothetic) group or the sub- or differential group, and then looking at individuality (either in a restricted way or, even more troublesome, as error variance). Such treatments of individuality occur in standard ergodic-theorems-based methods, for instance, in procedures that compare averages, such as analyses of variance. Instead, developmental scientists may begin to assess human development at the individual level and then assess whether it is legitimate (e.g., through finding evidence for the fit of structural models) to aggregate developmental phenomena at the differential or nomothetic level.

Accordingly, the assumption within an RDS approach to the development of a person is that the specific features that define that persons set of attributes are at least relatively plastic. The presence of such plasticity and the specificity of an individual adolescent, family, and adolescent^ family relationship provide a rationale for efforts (e.g., programs, policies) to enhance attributes of adolescent development in general and adolescent О family relations more specifically.

The alignment of the strengths of an individual young person and the strengths or developmental assets or resources of that persons family is the essence of Lerner and Lerner’s Positive Youth Development model (Lerner et al., 2015). This alignment between a unit or component of the relational developmental systems and the other facets of the dynamic system within which the unit is fused is also the essence of any approach to promoting positive human development—be it the development of an individual, family, school, community-based organization, or community itself (Lerner, 2004, 2018). In short, specificity principle—framed research focusing on the diversity of human development may be able to identify the specific adolescent<=>family relationships that are linked to positive development for specific individuals or families. With such information, developmental scientists can capitalize on the relative plasticity of human development and, by creating the conditions for such relations among other similar youth and families, promote more general positive development.

Conclusions

As we noted at the beginning of this article, the idea that humans possess nomothetic, differential, and idiographic attributes is not new (Kluckhohn & Murray, 1948). Nevertheless, these three domains of attributes have not been given equal attention in theory or research (e.g., Emmerich, 1968). The emphasis in the study of human behavior and development—whether of an individual or of groups—has been placed preponderantly on nomothetic attributes. As well, interest in group-differential phenomena has also been a longtime focus of scientific attention (e.g.. Block, 1971). However, for at least the past six or so decades, comparatively little attention has been given to the idiographic specificity' of human behavior and development and, therefore, to the study of person-specific features of that development (e.g., Rose, 2016).

This comparative scientific neglect continued despite appeals from leading scholars that omitting knowledge of the individual’s idiographic characteristics precluded a valid understanding of a person. For instance, Allport (1962) suggested that, to fully and veridically have a science of human behavior, researchers should

start with the individual behavior as a source of hunches (as we have

in the past), and then seek our generalizations (also as we have in the past), [and] finally come back to the individual—not for the mechanical application of laws (as we do now), but for a fuller, supplementary, and more accurate assessment than we are now able to give.

(p. 407)

Of course, we have argued that studying the specific attributes of an individual unit of analysis (a person or a relationship) provides much more significant information than just a hunch that might be supported by studying groups. Nevertheless, we agree—and have also argued—that by not systematically including in developmental analysis a focus on the idiographic attributes of a specific adolescent, family, or adolescent^ family relationship, fully valid (complete) assessment of development is not possible. Certainly, understanding of intraindividual (intraunit) changes that define development is obviated. Accordingly, we have endorsed the analyze-then- aggregate approach to the study of development that derives from the ideas of Molenaar and Nesselroade (2014, 2015) and Rose (2016): Analyze the intraindividual trajectories of change for a focal unit of analysis and then aggregate to differential or nomothetic levels of analysis when the tests of structural models provide data supporting such generalizations (e.g., through idiographic fdtering).

We recognize that the approach we are forwarding to the study of developmental science switches figure and ground in developmental analysis, as traditional analyses have focused on population statistics and the search for “laws,” or at least empirical generalizations, that are pertinent to samples that are as large as possible of individuals, families, or relationships (Emmerich, 1968). However, a figure-ground reversal is not just substantively appropriate and, now, methodologically feasible—it is also timely.

At the time of this writing, the Zeitgeist of contemporary social and behavioral science focuses increasingly on the diversity of humanity. Shouldn’t developmental scientists, then, prioritize attention to the major instantiation of diversity' that exists: The N of 1 that is represented by each adolescent, each, family, and each adolescent О family relationship?

Author Note

The preparation of this article was supported in part by grants from the Templeton Religion Trust and the Chan Zuckerberg Initiative. We are grateful to two anonymous JFTR reviewers for their helpful comments on a prior draft of this article.

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