The concept of development is the backbone of modern behavioral science. Psychiatric practitioners and behavioral scientists are concerned primarily with change, its origins, and its control. Developmental psychology is the scientific study of the structure, function, and processes of systematic growth and change across the life span. Systems of classification of behavior (including psychiatric nosology) take into account not only contemporaneous features and formal similarities among current symptoms and syndromes but also past qualities, immediate consequences, long-term outcome and likelihood of change (naturally or through treatment).
Whereas developmental psychology is concerned with species-typical patterns of systematic change (and central tendencies of the species), the discipline of developmental psychopathology is concerned with individual differences and contributes greatly to the understanding of childhood disorders.
The organizing framework of developmental psychopathology is a movement toward understanding the predictors, causes, processes, courses, sequelae, and environmental symbiosis of psychiatric illnesses in order to discover effective treatment and prevention. This movement is guided by in a developmental framework that integrates knowledge from multiple disciplines (e.g., psychobiology, neuroscience, cognitive psychology, social psychology) and levels of analysis (e.g., neuronal synapse, psychophysiologic response, mental representation, motor behavior, personality pattern). The relationship between developmental psychology and developmental psychopathology is reciprocal: The study of normal development gives context to the analysis of aberrations, and the study of psychopathology informs our understanding of normative development.
A developmental orientation forces a scholar to ask questions that move beyond the prevalence and incidence of disorders. Table 8–1 lists some of these questions.
The Orthogenetic Principle
The orthogenetic principle proposes that development moves from undifferentiated and diffuse toward greater complexity, achieved through both differentiation and consolidation within and across subsystems. The newborn infant is relatively undifferentiated in response patterns, but through development achieves greater differentiation (and less stereotypy) of functioning. Each period of development is characterized by adaptational challenges resulting from environmental demands (e.g., a mother who has become unwilling to breast-feed) and from emerging internal influences across subsystems (e.g., growing recognition of the self as able to exert control). The challenges are best conceptualized not as mere threats to homeostasis; rather, change and the demand for adaptation define the human species, and challenges push the individual toward development. The inherent adaptational response of the species is toward mastery of new demands. The mastery motive is as yet unexplained by science, although it is characteristic of the human species (see “Adaptation and Competence” section later in this chapter).
Thus, development is characterized by periods of disruption in the homeostasis of the organism brought on by new challenges, followed by adaptation and consolidation until the next challenge is presented. The adaptive child uses both internal and external resources to meet a challenge. Successful adaptation is defined as the optimal organization of behavioral and biological systems within the context of current challenges. Adaptation requires the assimilation of past organizational structures to current demands as well as the generation of new structures equipped to meet the demands.
Piaget described two types of change: assimilation, which involves incorporation of the challenge into existing organizational structures (e.g., an infant might treat all adults as the same kind of stimulus); and accommodation, which involves reorganization of the organism's structures to meet the demands of the environment (e.g., a developing infant learns to discriminate among adults and to respond differently to different adults) (see “Organismic Theory” section later in this chapter). Accommodation is more complex than assimilation, but successful adaptation requires a balance of both.
Maladaptation, or incompetence in responding to challenge, is characterized by the inadequate resolution of developmental challenges (as in the psychoanalytic concept of fixation). Maladaptation may be evidenced by developmental delays or lags, such as the continuing temper tantrums of an emotionally dysregulated child beyond the period when such behavior is normative. At any phase, the organism will manifest some form of regulation and functioning, even if it is not advantageous for future development. Thus, the child's tantrums might serve to regulate both a complex external environment of marital turmoil and an internal environment of stress. However, suboptimal regulation will prevent or hamper the individual from coping with the next developmental challenge.
Sometimes, apparently effective responses to a particular challenge lead to maladaptation at a more general level. Consider a toddler who responds to the withdrawal of a mother's undivided attention by ignoring her. Although this pattern of response may mean calmer evenings temporarily, the toddler will be ill equipped to respond to other challenges later in development. Consistent social withdrawal may cause the child to fail to acquire skills of assertion; however, continued ignoring of the mother may lead to a phenotypically distinct response in the future (e.g., depression in adolescence). Thus, the orthogenetic principle calls to mind the functioning of the’ entire organism (not merely distinct and unrelated subsystems) and the readiness of that organism to respond to future challenges.
Lerner, RM (ed): Theoretical models of human development. In: Handbook of Child Psychology, Vol 1. New York: Wiley, 2006.
Major Principles of Ontogeny & Phylogeny
Cairns and Cairns outlined seven principles that characterize the human organism in interaction with the environment over time: conservation, coherence, bidirectionality, reciprocal influence, novelty, within-individual variation, and dynamic systems. The first principle is that of conservation, or connectivity in functioning across time. Even with all the pressure to change, social and cognitive organization tends to be continuous and conservative. The constraints on the organism and the multiple determinants of behavior lead to gradual transition rather than abrupt mutation. Observers can recognize the continuity in persons across even long periods of time; that is, we know that a person remains the same “person.” For Piaget, who began his career by writing scientific papers on the evolution of mollusks, this within-person continuity principle is consistent with his view that species-wide evolution is gradual. Piaget believed that development within individuals reflects development of the species (i.e., ontogeny recapitulates phylogeny).
The second principle is coherence. Individuals function as holistic and integrated units, in spite of the multiple systems that contribute to any set of behaviors. One cannot divorce one system from another because the two systems function as a whole that is greater than its component parts. This fact is another conservative force, because an adverse effect on one part of a system tends to be offset by compensatory responses from other parts of the system. This phenomenon applies to all human biological systems and can be applied to psychological functioning.
The third principle is a corollary of the second: Influence between the organism and the environment is bidirectional. The person is an active agent in continuous interaction with others. Reciprocal influences are not identical; rather, at each stage of development, the person organizes the outer world through a mental representational system that mediates all experience with the world. Nevertheless, reciprocity and synchrony constrain the person, and the relative weight of these constraints varies at different points in development. At one extreme, it is possible to speak of symbiosis and total dependency of the infant on the mother; at the other extreme, behavior geneticists refer to genetic effects on environmental variables (such as the proposition that genes produce behavior that leads to the reactions that one receives from others in social exchanges).
Another corollary of the second principle is the principle of reciprocal influence between subsystems within the individual. Behavioral, cognitive, emotional, neurochemical, hormonal, and morphologic factors affect each other reciprocally. Mental events have biological implications and vice versa. Among the most exciting research directions in developmental psychopathology has been afforded by the technology of functions magnetic resonance imaging (fMRI), which enables the understanding of how environmental stimuli and behavioral displays are mediated through brain activity.
The fifth principle of ontogeny is that novelty arises in development. Change is not haphazard. The forces of reciprocal interaction within the individual and the environment lead not only to quantitative changes in the individual but also to the emergence of qualitatively distinct forms, such as locomotion, language, and thought. These changes represent growth rather than random events, in that previous forms typically remain and are supplemented by novel forms.
The sixth principle of phylogeny is that of within-individual variation in developmental rates across subsystems. Change within a subsystem occurs nonlinearly, as in language development or even physical growth. Some of this nonlinearity can be explained by species-wide phenomena, such as puberty, but much of it varies across individuals. In addition, rates of change vary within an individual across subsystems. Consider two young children, identical in age. Child A may learn to crawl before child B, but child B might catch up and learn to walk before child A. Likewise, child B might utter a recognizable word before child A, but child A might be talking in sentences before child B. This unevenness within and across individuals characterizes development and makes predictions probabilistic rather than certain. Some of the variation is attributable to environmental factors that have enduring personal effects (such as the lasting effects on cognitive achievement of early entry into formal schooling) or biological factors that have enduring psychological effects (such as the effect of early puberty on social outcomes), whereas other factors may have only temporary effect (such as efforts to accelerate locomotion onset) or no effect at all.
Finally, according to the seventh principle, development is extremely sensitive to unique configurations of influence, such as in dynamic systems. Growth and change cannot be reduced to a quantitative cumulation of biological and environmental units. Also, development is not simply hierarchical, with gradual building of functions on previous ones. Rather, development often follows a sequence of organization, disorganization, and then reorganization in a different (possibly more advanced) form. In physical sciences, this principle is called catastrophe theory, reflecting the hypothesis that during the disorganization, events are literally random. But reorganization occurs eventually, in lawful and predictable ways.
Dynamic systems theory incorporates several postulates about growth and change. First, change occurs nonlinearly. Second, minor quantitative changes can lead to dramatic qualitative changes in state. Consider how flow of water from a spigot changes from a succession of droplets to a stream or how water itself turns to ice. These major qualitative shifts occur in a regulated way with only minor qualitative changes in a parameter. Third, microlevel events that occur repeatedly often precipitate macrolevel changes in an organism's state.
Granic and Patterson (2006) have described how dynamic systems theory contributes to our understanding of the development of serious conduct disorder. Early difficult temperament and minor conduct problems sometimes shift dramatically to serious violence and antisocial personality disorder through a series of subtle changes in the microlevel characteristics of a parent–child relationship. Coercive exchanges, positive reinforcement, and capitulation by one party at a microlevel can lead a child to emerge from the interaction with macrolevel changes in the propensity for antisocial behavior in other relationships.
Cairns RB, Cairns BD: Lifelines and Risks: Pathways of Youth in Our Time. New York: Cambridge University Press, 1994.
Granic I, Patterson GR: Toward a comprehensive model of antisocial development: A dynamic systems approach. Psychol Rev
A simple but powerful developmental concept that has affected psychiatric nosology is that of age norms. Rather than evaluating a set of behaviors or symptoms according to a theoretical, absolute, or population-wide distribution, diagnosticians increasingly use age norms to evaluate psychiatric problems. Consider the evaluation of temper tantrums. In a 2-year-old child, tantrums are normative, whereas in an adult, angry outbursts could indicate an intermittent explosive disorder or antisocial personality. More subtle examples affect the diagnosis of many disorders in the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV), such as attention-deficit/hyperactivity disorder, mental retardation, and conduct disorder. With regard to major depressive episodes and dysthymic disorder, age-norming has resulted in consideration of different symptoms at different ages in order to diagnose the same disorder (e.g., irritability and somatization are common in prepubescent depression, whereas delusions are more common in adulthood). DSM-IV explicitly requires consideration of age, gender, and culture features in all disorders, suggesting the importance of evaluating symptoms within the context of their expression.
The importance of age-norming suggests the need for empirical studies of symptoms in large epidemiologic samples and the linking of research on normative development to psychopathology. In this way, developmental psychopathology is similar to psychiatric epidemiology (see Chapter 5). Despite the increased emphasis on age-norming, ambiguity pervades current practice. DSM-IV defines disorders in terms of symptoms that are quantified as “often,” “recurrent,” and “persistent” without operational definition. Some clinicians intuitively contextualize their use of the term “often” relative to a child's agemates (so that “often displays temper tantrums” might mean hourly for a 2-year-old child and weekly for a teenager), whereas other clinicians do not (so that “often” has the same literal meaning across all ages). The “specific meaning of these terms is not clear in the context of some DSM-IV disorders. Complete age-norming might imply the removal of all age differences in prevalence rates (reducing disorder merely to the statistical extremes of a distribution at an age level), whereas complete neglect of age norms implies that at certain ages a disorder is ubiquitous. To resolve these problems, developmental researchers need to learn which patterns of symptoms ought to be examined epidemiologically, and psychopathologists need to compare their observations to empirical norms.
American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, 4th edn. Washington DC: American Psychiatric Association, 1994.
Diagnosticians must consider not only the age-normed profile of symptoms but also the developmental trajectories of those symptoms (both age-normed and individual). For example, consider three 10-year-old children who exhibit aggressive behavior. As depicted in Figure 8–1, child A has displayed a relatively high rate of aggression historically, but the trajectory is downward. Child B has displayed a constant rate of aggressive displays, and child C's aggressive displays have accelerated geometrically. Which child has a problematic profile? The diagnostician will undoubtedly want to consider not only current symptom counts (in relation to age norms) but also the developmental trajectory of these counts (and the age norm for the trajectory). Child C might be most problematic because of the age trend, unless this trend were also age normative (e.g., some increase in delinquent behavior in adolescence is certainly normative). In contrast, child B's constant pattern might be problematic if the age-normed trend were a declining slope.
Three hypothetical developmental trajectories for aggressive behavior.
Some DSM-IV disorders explicitly take into account the trajectory of an individual's symptoms. For example, Rett's disorder, childhood disintegrative disorder, and dementia of the Alzheimer's type involve deviant trajectories. The diagnosis of other disorders may require trajectory information that is not yet available. This information must be based on longitudinal study of individuals and not cross-sectional data, because only longitudinal inquiry allows for the charting of growth curves within individuals over time. Population means at various ages indicate little about within-individual changes. Population-wide symptom counts might grow systematically across age even when individual trajectories are highly variable.
Recent advances in quantitative methodology have enabled researchers to identify trajectories of development that mark different risk. Growth curve analyses are being used to identify predictors of trajectories so that dimensions can forecast future change in behavior based on normative profiles.
Costello EJ: Developments in child psychiatric epidemiology. J Am Acad Child Adolesc Psychiatry
Nagin DS: Analyzing developmental trajectories: A semi-parametric, group-based approach. Psychol Methods 1999;4:139.
The Boundary between Normal & Abnormal
One of the tenets of developmental psychology is that a knowledge of normal development informs psychopathology partly because the boundaries between normal and abnormal are sometimes vague, diffuse, or continuous. Many disorders (e.g., conduct disorder, dysthymic disorder) are defined on the basis of cutoffs in dimensional criteria rather than on qualitative distinctions that are more easily recognizable. Criteria such as “low energy” and “low self-esteem” (for dysthymic disorder) and “marked or persistent fear” (for social phobia) are matters of degree. One of the central questions is where to locate the boundary between normal and abnormal when the criteria of psychopathology are dimensional.
In some cases, the boundary is arbitrary. In other cases the “true” boundary might be identified on the basis of three considerations: (1) a noncontinuous pattern of the distribution of scores, (2) a qualitatively distinct change in functioning that accompanies a quantitative difference in a score, or (3) unique etiology at the extreme of a distribution.
The first consideration is whether the population of scores is distributed normally with a single mode or bimodally with an unusually large number of cases at one extreme. A large number of cases at one extreme would suggest that a second causal agent is operating, beyond whatever agent caused the normal distribution. A second causal agent might suggest a deviant (i.e., psychopathologic) process. Consider the relation between the intelligence quotient (IQ) score (a continuous measure) and mental retardation. The distribution of IQ scores in the U.S. population is not normal. Far more cases of IQs below 70 occur than would be expected by a normal distribution. Thus, the distinction between normal and abnormal IQ scores is not merely one of degree.
The second consideration is whether qualitative differences in functioning occur with quantitative shifts in a criterion. For example, if a decrement of 10 IQ points from 75 to 65 makes it significantly more difficult for a child to function in a classroom than a decrement from 100 to 90, then a case can be made for locating the cutoff point near an IQ of 70.
The third consideration is the possible distinct etiology of scores at an extreme end of the distribution. A single set of causes will ordinarily lead to a normal distribution of scores. A disproportionate number of scores at an extreme often suggests a separate etiology for those scores. In the case of IQ scores, one set of forces (e.g., genes, socialization) leads to a normal distribution, whereas a second set of forces (e.g., Down syndrome, anoxia, lead toxicity) leads to a large number of cases at the low extreme.
Cicchetti D, Toth SL: Developmental psychopathology and preventive intervention. In: Renninger KA, Sigel IE (Vol eds). Handbook of Child Psychology 2006, p. 497; New York.
A vexing problem highlighted by research in developmental psychology is that some disorders involve multiple etiologic pathways. The principles of equifinality and multifinality, derived from general systems theory, hold for many disorders. Equifinality is the concept that the same phenomenon may result from several different pathogens. For example, infantile autism results from congenital rubella, inherited metabolic disorder, or other factors. Multifinality is the concept that one etiologic factor can lead to any of several psychopathologic outcomes, depending on the person and context. Early physical abuse might lead to conduct disorder or to dysthymic disorder, depending on the person's predilections and the environmental supports for various symptoms; poverty predisposes one toward conduct disorder but also substance abuse disorder.
The diversity in processes and outcomes for disorders makes the systematic study of a single disorder difficult. Unless scholars consider multiple disorders and multiple factors simultaneously, they cannot be sure whether an apparent etiologic factor is specific to that disorder. Inquiry into one disorder benefits from a conceptualization within a larger body of development of normal adjustment versus problem outcomes. The broad coverage of developmental psychology provides the grounding for inquiry into various disorders.
Rutter M: Psychosocial resilience and protective mechanisms. In: Rolf J, Masten AS, Cicchetti D, Nüchterlein K, Weintraub S (eds). Risk and Protective Factors in the Development of Psychopathology. New York: Cambridge University Press, 1990.
The discovery of biosocial interactions in psychiatric disorders has been labeled one of the most important discoveries on all of science in the past decade. Not only are multiple distinct factors implicated in the genesis of a disorder, the profile of factors often conspires to lead to psychopathologic outcomes. Empirically, this profile is the statistical interaction between factors (in contrast with the main effects of factors). Thus, a causal factor might operate only when it occurs in concert with another factor. For example, the experience of parental rejection early in life is a contributing factor in the development of conduct disorder but only among that subgroup of children who also display a biologically based problem such as health difficulties at the time of birth. Likewise, health problems at birth do not inevitably lead to conduct disorder; the interaction of a biologically based predisposition with a psychosocial stressor is often required for a psychopathologic outcome.
Caspi et al. (2002) hypothesized that risk for conduct disorder grows out of the early experience of physical maltreatment, but only among a subpopulation characterized by polymorphism in the gene encoding the neurotransmitter-metabolizing enzyme monoamine oxidase A (MAOA). They found that physically maltreated children with a genotype conferring high levels of MAOA expression were less likely to develop antisocial problems than children without this genotype. These findings help us understand why not all victims of maltreatment grow up to victimize others, and they also indicate that environmental experiences may be necessary to potentiate the action of a genotype.
The same group of researchers has discovered a biosocial interaction in the development of depressive disorder. Life stressors precipitate the onset of depressive episodes, but only among a subpopulation characterized by a functional polymorphism in the promoter region of the serotonin transporter (5-HT T) gene. Individuals with one or two copies of the short allele of the 5-HT T promoter polymorphism exhibit more depressive symptoms, diagnosable depression, and suicidality in response to stressful life events than individuals homozygous for the long allele. The importance of biosocial interactions suggests the importance of examining multiple diverse factors simultaneously, both in empirical research and clinical practice.
Caspi A, McClay J, Moffitt TE, et al.: Role of genotype in the cycle of violence in maltreated children. Science
Caspi A, Sugden K, Moffitt TE, et al.: Influence of life stress on depression: Moderation by a polymorphism in the 5-HTT gene. Science
Critical Periods & Transition Points
A critical period is a point in the life span at which an individual is acutely sensitive to the effects of an external stimulus, including a pathogen. Freud argued that the first 3 years of life represent a critical period for the development of psychopathology, through concepts such as regression, fixation, and irreversibility. The concept of critical stages gained credence with studies of social behavior in animals by the ethologist Lorenz and the zoologist Scott. This concept is part of several central theories of social development, such as Bowlby's attachment theory (discussed later in this chapter). The rapid development of the nervous system in the first several years, coupled with relatively less neural plasticity in subsequent years, renders this period critical. The effects of exposure to lead and alcohol, for example, are far more dramatic when the exposure occurs in utero or in early life.
A variation of the concept of a critical period is the hypothesis of gradually decreasing plasticity in functioning across the life span. As neural pathways become canalized, mental representations become more automatic and habits form. However, the notion of the primacy of early childhood has been thrown into question by empirical data that indicate greater malleability in functioning than was previously thought. Rutter, for example, suggests that a positive relationship with a parental figure is crucial to the prevention of conduct disorder and that this relationship can develop or occur at any point up to adolescence, not just during the first year of life.
Some developmental psychologists have argued for other critical periods in life, such as puberty and giving birth as critical periods for the development of major depressive disorder in women, although this assertion has been contested. Critical periods might be defined not only by biological events but also by psychosocial transitions. Developmental psychologists have increasingly recognized the crucial role of major life transitions in altering developmental course, accelerating or decelerating psychopathologic development, and representing high-risk periods for psychopathology. These transition points include but are not limited to entry to formal schooling, puberty and the transition to junior high school, high school graduation and entry into the world of employment, marriage, birth of children, and death of loved ones (particularly parents or spouse). These transitions have been associated with elevated risk for some forms of psychopathology. One task of developmental psychologists is to discover which life transitions are most crucial and how these transitions alter the course of development of some but not other forms of psychopathology.
Kandel ER, Hawkins RD: Neuronal plasticity and learning. In: Broadwell RD (Vol ed). Decade of the Brain. Vol 1: Neuroscience, Memory, and Language. Washington DC: Library of Congress, 1995.
One of the most important contributions of developmental psychology has been the discovery that patterns of behavior, and of process–behavior linkage, vary across contexts. In the context of U.S. society, a child who is teased by peers might find support for retaliating aggressively, whereas the same teasing experience in Japanese society might cause shame, embarrassment, and withdrawal. Thus, reactive aggressive behavior might be stigmatized as psychopathology in one culture but not another. Context shapes single behaviors and may also shape patterns of psychopathology.
Context also provides the frame or ground through which individual behaviors are given meaning. For example, a child interprets a parent's discipline in relation to norms that are observed culture-wide. In cultures that endorse the use of corporal punishment as appropriate, a child who is punished in this manner (at mild, nonabusive levels) is not at particularly high risk for anxiety problems or conduct problems. However, in cultures that do not endorse this type of parenting, a child who is corporally punished is likely to interpret it as a signal that the parent rejects the child as aberrant or is an aberrant parent, and either interpretation is likely to lead to anxiety and conduct problems.
Context can be defined at many levels, from discrete situational features to broad cultural features and from internal states such as mood to external factors such as geography or time of day. Bronfenbrenner's continuum of environmental contexts forms the basis of his ecological theory (discussed later in this chapter).
Bronfenbrenner U: The Ecology of Human Development: Experiments by Nature and Design. Cambridge, MA: Harvard University Press, 1979.
Dodge KA, Coie JD, Lynam D: Aggression and antisocial behavior in youth. In: Damon W (Series ed), Eisenberg N (Vol ed), Handbook of Child Psychology, Vol. 3. Social, Emotional, and Personality Development, 6th edn. New York: Wiley, 2006, pp. 719–788.
Lansford JE, Chang L, Dodge KA, et al.: Physical discipline and children's adjustment: Cultural normativeness as a moderator. Child Dev
Research in developmental psychology has sometimes enabled sharper distinctions between normal and abnormal (such as when a genetic marker of a disorder is identified), but more often it has articulated the continuity between normal and abnormal. Research has suggested that disorders might be defined less by noncontextualized behavioral criteria (e.g., a score on an IQ test) and more by an assessment of the individual's level of adaptation and functioning. This concept has been embraced by the term competence, or adaptive functioning, which is the level of performance by an individual in meeting the demands of his or her environment to the degree that would be expected given the environment and the individual's age, background, and biological potentials.
Empirical research has shown that measures of childhood social competence are important predictors of adolescent psychiatric disorders, including conduct disorder and mood disorders. Impaired social competence is a premorbid marker for the onset of schizophrenia and is a predictor of relapse.
The concurrent importance of adaptive functioning is so obvious that this concept has become part of the diagnostic criteria for some disorders. For example, a diagnosis of mental retardation requires impairment in adaptive functioning above and beyond the score on an IQ test. A diagnosis of generalized anxiety disorder requires impairment in social functioning in addition to the absolute pattern of anxiety. A diagnosis of obsessive–compulsive disorder requires marked personal distress or significant impairment in functioning. Some broad definitions of mental disorder are based on a general assessment of an impairment in adaptive functioning due to cognitive or emotional disturbance.
Kazdin AE: Conduct Disorders in Childhood and Adolescence. Thousand Oaks, CA: Sage, 1995.
Kupersmidt JB, Dodge KA (eds): Children's Peer Relations: From Development to Intervention. Washington, DC: American Psychological Association, 2004.
Risk Factors & Vulnerability
Epidemiologic and developmental researchers have introduced the notion of risk factors to identify variables known to predict later disorder (see Chapter 5). A risk factor is defined by its probabilistic relation to an outcome variable, without implying determinism, early onset of disorder, or inevitability of outcome. Risk factors are either markers of some other causal process or causal factors themselves. One goal of developmental research is to determine the causal status of risk markers. As noted earlier in this chapter, social competence, or level of adaptive functioning, is a broad risk factor for many disorders, but empirical research must determine whether this factor merely indicates risk that is caused by some other factor (e.g., genes) or constitutes a contributing factor in itself.
Risk factors often accumulate in enhancing the likelihood of eventual disorder. For example, the probability of conduct disorder is enhanced by low socioeconomic status, harsh parenting, parental criminality, marital conflict, family size, and academic failure. The number of factors present seems to be a stronger predictor of later disorder than is the presence of any single factor, suggesting that causal processes are heterogeneous and that risk factors cumulatively increase vulnerability to a causal process.
The concept of vulnerability has been applied to individuals who are characterized by a risk factor. Many empirical studies of the development of disorder use samples that are defined by a risk factor (such as offspring of alcoholics and first-time juvenile offenders); however, it is not clear that the causal and developmental factors are similar in disordered individuals who come from high-risk and low-risk populations.
Biederman J, Milberger S, Faraone SV, et al.: Family-environment risk factors for attention-deficit hyperactivity disorder. Arch Gen Psychiatry
Cicchetti D, Cohen DJ (eds): Developmental Psychopathology, Vols. 1–3. New York: Wiley, 2006.
Developmental psychologists study the causal process through which disorder develops. The identification of a risk factor does not necessarily imply a causal process for these reasons: (1) a risk factor might be a proxy for a causal factor and empirically related to a disorder only because of its correlation with this causal factor (the so-called third-variable problem), (2) a risk factor might occur as an outcome of a process that is related to a disorder rather than as the antecedent of the disorder, or (3) a risk factor might play a causal role in a more complex, multivariate process. Indeed, individuals who are predisposed to a disorder often select environments that are congruent with the disorder. The environment might appear to “cause” the disorder but instead merely be a marker of risk. Therefore, developmental psychologists often attempt to understand the process through which risk factors are related to eventual disorder. The factors that are identified as intervening variables in this process are called mediators, or variables that account for (or partially account for) the statistical relation between a risk factor and a disorder.
Four empirical steps are required to demonstrate at least partial mediation (Figure 8–2). First, risk factor A must be empirically related to outcome C (i.e., there must be a phenomenon to be mediated, called the total effect). Second, A must be related to mediator B. Third, B must be related to C. Finally, in a stepwise regression or structural equation model analysis, when B has been added to the prediction of C, the resulting relation between A and C (called the direct effect) must be reduced significantly from the original bivariate relation. The difference between the total effect and the direct effect is called the indirect effect, that is, the magnitude of the mediation of the effect of A on C by B.
Mediation of the effect of physical abuse on the development of conduct disorder.
An example (depicted in Figure 8–2) is the biased pattern of social information-processing that often results from an early history of physical abuse. Early abuse (A) is a known risk factor for the development of conduct disorder (C) (i.e., it is statistically correlated with later conduct disorder, but many abused children do not develop this disorder nor do all persons who have conduct disorder show a history of abuse). Early abuse is also correlated with the development of a social information-processing pattern (B) of hypervigilance to threatening cues, perceiving the social world as a hostile and threatening place, and poor social problem-solving skills. These mental factors (B) are associated statistically with later conduct disorder (C) and account for about half of the effect of early abuse (A) on later conduct disorder (C).
Baron RM, Kenny DA: The moderator-mediator variable distinction in social psychological research: Conceptual, strategic, and statistical considerations. J Pers Soc Psychol 1986;51:1l73.
Dodge KA, Pettit GS: A biopsychosocial model of the development of chronic conduct problems in adolescence. Dev Psychol
Moderators & Protective Factors
Rutter found that the effect of a risk factor on a disorder can vary across contexts, populations, or circumstances. That is, the magnitude of an effect might be reduced (or enhanced) under different conditions. For example, the effect of early harsh discipline on the development of conduct disorder is reduced under circumstances of a warm parent–child relationship. This phenomenon is called a moderator effect and is defined by a significant interaction effect between a risk factor and a moderating factor in the prediction of a disorder.
Moderator variables have also been called protective, or buffering, factors. A protective factor protects, or buffers, the individual from the pathogenic effects of a risk factor. Intelligence and a positive relationship with a caring adult have been the most commonly studied protective factors for a variety of disorders. One remaining question is whether protective factors operate more strongly in high-risk than in low-risk groups; that is, if a variable buffers both low-risk and high-risk groups from risk, it is not clear whether that variable would be defined as a protective factor (or simply another predictor variable).
Rutter M, Sroufe LA: Developmental psychopathology: Concepts and challenges. Dev Psychopathol
Intervention & Prevention as Experiments
There is a reciprocal relation between the scientific study of behavior in developmental psychology and the application of scientific principles to psychiatry. Concepts from developmental psychology have been applied in psychiatric practice, but psychiatric intervention can also be viewed as a field experiment to test hypotheses about behavioral development. Systematic intervention and prevention can be viewed as experiments to test basic principles. In fact, given the complexity of human behavioral development and the ethical restraints against known iatrogenic manipulations, clinical practice may be the most powerful scientific tool available to test hypotheses from developmental psychology. Thus, the relation between these disciplines is reciprocal, and communication between the disciplines must be preserved.
Cicchetti D, Toth SL: Developmental psychopathology and preventive intervention. In: Renninger KA, Sigel IE, (Vol eds). Handbook of Child Psychology, 2006, p. 497, New York: Wiley.