Evidence for Can Found When Adopted Children Behavior Resembles Their Adopted Families Behavior
Alcohol Health Res World. 1995; xix(three): 195–200.
Adoption Studies
Abstract
Researchers use adoption studies to determine the contributions of genetic and environmental factors to the development of alcohol problems. These studies more often than not compare the outcomes of adoptees who take biological parents with alcohol problems and who grow up in various adoptive environments with the outcomes of adoptees without such family backgrounds but raised in similar environments. Using certain statistical approaches, adoption studies too allow for the evaluation of specific gene-environment interactions in determining an event such as alcoholism. To obtain data that let meaningful and generalizable conclusions, however, scientists must select a representative grouping of study subjects, obtain valid information near these subjects from a broad diverseness of sources, and consider biases inherent in adoption practices.
Keywords: adoption study, AODR (alcohol and other drug related) bug, hereditary factors, ecology factors, research and evaluation method, behavioral problem, factor
Adoption studies are a powerful tool for evaluating the interactions of genetic and ecology factors in eliciting human being characteristics, such as intelligence (i.e., IQ), and disorders, such as alcoholism. The relative importance of "nature" (i.e., genetic inheritance) versus "nurture" (i.eastward., the rearing surround) in homo behavior was beginning debated at the starting time of this century. Simultaneously, some techniques were adult that are still used to study the inheritance of behaviors, including the family study; the twin study (see the article past Prescott and Kendler, pp. 200–205); and statistical methods, such equally regression analysis. One pioneer of human being genetics, Sir Francis Galton, used these techniques in his studies. Galton concluded from his investigations that "nature prevails enormously over nurture" (Pearson 1914–thirty). In 1912, 1 yr after Galton's death, another researcher, L.F. Richardson, proposed to study children who had been separated from their birth parents in order to investigate the inheritance and development of intelligence (Richardson 1912–13).
Concurrent social changes led to greater public credence of adoption and also improved researchers' access to adoptees. For instance, foundling societies and orphanages promoted adopting orphans or children born out of wedlock into foster families who were by and large nonrelatives. Adoptive parents usually received little data about the adoptees' biological parents. The lack of information may have been attributable to the conventionalities at that time in the surroundings'southward overwhelming importance on a child's development. In add-on, having a child out of marriage was considered shameful, and consequently, confidentiality protected the birth mother. These "closed" adoptions were advantageous for conducting adoption studies because they clearly separated the biological and environmental influences on the adoptee.
In contrast, during the past two decades, a move has occurred toward more "open up" adoptions, in which biological and adoptive parents receive data well-nigh each other. Furthermore, this blazon of adoption may encourage standing contact of the nativity parents with both the adoptee and the adoptive family. In improver, social changes have drastically reduced the number of infant adoptees. For instance, near unwed mothers now keep their children rather than give them upward for adoption. These developments have increased the practical problems involved in finding and recruiting suitable adoptees for studies.
Betwixt the 1930's and 1950's, most adoption studies examined the heritability and furnishings of environmental influences on IQ. For example, during the 1930's, Skodak and Skeels (1949) demonstrated increases in IQ in sure environments using an adoption epitome.ane Since the 1960'due south, however, adoption studies have been used primarily to demonstrate the importance of genetic factors in psychopathological disorders, such as schizophrenia, alcoholism, or depression (for review, run across Cadoret 1986). This article briefly examines some of the principles of adoption studies and the considerations required for their effective evaluation.
Influences on Adoptees' Behavior
The force of the adoption blueprint—separating genetic from environmental influences on a person's development—results from removing the child (ideally at birth) from the birth parents and their environs into a different environs with biologically unrelated adoptive parents. Thus, adoption studies assess "real-world" influences on the adoptee'southward development while allowing for the separation of genetic and environmental factors that are confounded when children are reared to machismo by their birth parents.
The adoptee'southward development and behavioral outcome result from multiple influences exerted by the birth parents and their environs and by the adoptive parents and their environment (for more than information on these influences, run into sidebar, p. 199). Determining the contributions of these unlike influences is a multivariate statistical problem. Several statistical techniques, such as multiple regression analysis and log-linear analysis, tin address such problems and have been used in evaluating adoption studies. Bohman, Cloninger, and their research group pioneered the use of multivariate approaches for studying the genetics of alcoholism in their analyses of Swedish adoption data (Bohman et al. 1982; Cloninger et al. 1982; Sigvardsson et al. 1982). Using these methods, the investigators assessed the contributions of both genetic and ecology factors on the evolution of alcoholism in the adoptees.
Selective Placement and Other Confounding Factors
To allow valid conclusions about the relative influences of genes and environment on adoptee event, information technology is essential that factors originating from the birth parents and their surroundings are unrelated to, and do not collaborate with, factors originating from the adoptive surround. This condition could be fulfilled by randomly placing infants in adoptive homes. However, adoption usually is not a random process. Adoption agencies carefully screen adoptive parents, and practical placement decisions frequently result in the selection of older, more than stable families; families in higher socioeconomic brackets; and intact, rather than unmarried-parent, families. Conversely, families that give up children for adoption commonly are single-parent, low-income ones.
In addition, adoptees may exist matched to prospective adoptive parents depending on a variety of factors. For instance, at one time adoptees ofttimes were matched with adoptive parents based on concrete characteristics, such as hair and eye color. Other, more subtle matchings could depend on psychosocial characteristics. For example, an adoption bureau might estimate a kid'southward "potential" from birth-parent characteristics (due east.g., education or socioeconomic level) and identify the child according to some expectation of future functioning. Finally, racial and indigenous origins also could play a office in placement decisions. These practices, referred to as "selective placement," could derange the normal contributions of biological and environmental factors. This possibility has led to criticism of adoption studies (Lewontin et al. 1984).
Design and Evaluation of Adoption Studies
Adoption studies generally can be classified based on whether the adoptees or the birth parents are the probands (i.e., the initial subjects) of the study (Rosenthal 1970). In the adoptees' study method, researchers identify proband nascency parents with a certain characteristic (east.g., alcoholism) and and then examine the outcome of these probands' adopted-abroad children. A contrasting design is the adoptees' family unit method, in which researchers place proband adoptees with a sure characteristic (eastward.m., alcoholism or depression) and subsequently examine both the birth and adoptive parents. Both designs take been used to demonstrate the importance of genetic factors in the development of alcoholism. Whether the adoptees' study method or the adoptees' family unit method is used often depends on certain considerations, such as practicality and the ease of recruiting probands and gathering information nigh them.
Most adoption studies have used a blueprint comparing loftier-risk probands (i.eastward., adoptees or birth parents) having certain characteristics (e.one thousand., alcoholism) with a control group of subjects who lack the pathology of the high-risk grouping and are considered "normal." In the adoptees' study design, researchers ordinarily compare the outcome of adoptees with contrasting biological backgrounds (e.yard., alcoholic versus nonalcoholic nascency parents); farther control tin can exist obtained by matching the proband and control birth parents on variables such every bit socioeconomic level or age. In the adoptees' family design, the study compares the biological backgrounds of proband adoptees with those of control adoptees, who usually have been selected for normality. In addition, the adoptees may be matched on variables such every bit age, gender, and socioeconomic level.
A typical adoptees' written report design compares then-chosen alphabetize adoptees—developed adoptees who accept backgrounds of psychopathology (e.thousand., alcoholism) in their biological families—with age- and sex-matched control adoptees who accept no family histories of psychopathology. (For a more than detailed description of the design of an adoptees' report paradigm, come across effigy i.) An adoption study by Cadoret and colleagues (1987) illustrates how the contributions of several genetic and environmental factors to the development of alcoholism can be determined using this method (figure 2). In the study, 160 male adoptees, their biological relatives, and their adoptive families were analyzed regarding booze bug, antisocial behavior, and other psychological variables. The written report establish that a genetic influence, such as alcohol bug in start-caste (i.e., parents) or second-degree (i.eastward., grandparents) biological relatives, increased an adoptee's risk for alcohol problems 4.half-dozen-fold. Similarly, an environmental influence, such as alcohol problems in a member of the adoptive family, resulted in a 2.7-fold college hazard for booze problems in the adoptee, compared with adoptive families without alcohol problems.
An example of an adoption study using the adoptees' study method comparing two groups of adoptees: alphabetize adoptees and control adoptees.
Results of an adoptees' written report method adoption paradigm based on 160 male adoptees and their biological and adoptive families assessed for alcoholism, antisocial personality disorder, and other psychological parameters. The numbers side by side to the arrows are odds ratios.1 (For example, an adoptee with showtime- or second-caste biological relatives with booze problems is 4.vi times more probable to abuse alcohol than an adoptee without such a family unit background.)
* p < 0.05
** p < 0.01
*** p < 0.001
iAn odds ratio is a measure of clan between 2 variables.
SOURCE: Adapted from Cadoret et al. 1987.
Because the adoption agencies frequently were enlightened of both alcoholism and antisocial behavior in the biological parents, these factors could have influenced placement decisions and correlated with the environmental factor of adoptive family alcohol issues. To control for such potential selective placement effects, the correlations betwixt alcohol issues or antisocial beliefs in the biological family and alcohol issues in the adoptive family likewise were assessed in the statistical assay (effigy ii). The report found no evidence of selective placement based on the factors shown: As indicated by the odds ratios2 of 1.0, the likelihood of a fellow member of the adoptive family unit having alcohol problems was the same whether or non biological relatives of the adoptee displayed alcohol issues or antisocial behavior.
Assortative Mating
Another factor that tin bear on a child'due south evolution and behavior is assortative mating (i.eastward., the nonrandom pick of a partner based on personal characteristics). For example, an alcoholic person may be more likely than a nonalcoholic person to take an antisocial or alcoholic partner, perchance considering of shared traits or behaviors. The combination of two genetic predispositions may enhance the predisposition of the offspring to develop whatever psychopathology. Multivariate statistical analyses can help control for the furnishings of assortative mating if relevant information is available on both birth parents. Similar analyses also can exist used to control for the genetic predisposition for two disorders (due east.g., alcoholism and antisocial personality disorder) within one person.
Alternative Evaluation Methods
Simpler statistical analyses also have been used to evaluate the results of adoption studies. For example, when the assessment of genetic influences is the primary objective, a common strategy is to demonstrate that the environmental influences are the aforementioned for adoptees from loftier-take a chance backgrounds (i.e., with alcoholic biological family members) and depression-risk backgrounds (i.eastward., without alcoholic biological family unit members). Comparable environmental factors for both groups would indicate that no selective placement occurred that could confound the report results. Using this method, Goodwin and colleagues (1973) demonstrated the importance of a genetic predisposition to the development of alcoholism. However, although environmental influences may be similar when averaged over high- or low-risk adoptee groups, considerable environmental variability still exists amongst the members of each adoptee group that could affect the outcome of private adoptees and which should be assessed by multivariate statistical approaches.
Gene-Surround Interactions
In determining the contributions of genetic factors to an event such as alcoholism, it is of import to know whether a genetic factor exerts its consequence only in the presence of a specific environmental condition or does then independently of surroundings. The adoption prototype is a powerful tool for evaluating the interaction of specific genetic factors with specific environmental factors that affect adoptee effect (DeFries and Plomin 1978). For example, researchers and clinicians take long recognized that both conduct disorder and aggressivity predispose an afflicted person to alcohol and other drug corruption (see figure ii). Adoption studies as well take demonstrated that hating personality disorder in nascency parents predisposes adopted-away offspring to both deport disorder (Cadoret and Cain 1981; Cadoret 1986) and aggressivity (Cadoret et al. 1995). In the latter study, however, the genetic predisposition inherited from a birth parent with antisocial personality disorder increased behave disorder and aggressivity only in adoptees raised in an environment with additional adverse factors (due east.g., an adoptive parent suffering from a psychiatric or marital problem) (figure 3) (Cadoret et al. 1995).
Correlation between antisocial personality disorder in a nascence parent, adverse ecology factors in the adoptive abode (i.due east., marital, legal, psychiatric, or substance abuse problems in the adoptive parents), and adolescent aggressivity in the adoptee. If a nascence parent has an antisocial personality, a positive correlation exists between adverse environmental factors and aggressivity symptoms in the adoptee. This correlation is significantly different when none of the nascency parents has an hating personality.
SOURCE: Adapted from Cadoret et al. 1995.
Findings from the study of this blazon of gene-surround interaction may suggest points of intervention, thereby helping to foreclose beliefs leading to alcoholism. For example, in the above example, modifications of the environment (due east.thou., treatment of the adoptive parents' problems) could touch on the adoptee'south issue even in the presence of a genetic predisposition.
Factors Influencing Study Quality
Obtaining Valid Information
Valid information about the nascency parents, the adoptive parents, and the rearing environs is crucial when using adoption studies to assess the influences of genetic and environmental factors on beliefs. This data must address the four important sources of influences on the adoptee: the genetic and environmental factors from the nascency parents, the parental influences from the adoptive parents, and the adoptive family environment. Thus, a major technical difficulty in adoption studies is arranging for data collection from a broad range of sources, some of which are protected by confidentiality.
Information nigh the birth parents and their behaviors is necessary to decide which adoptee characteristics may correspond phenotypes of a genetic predisposition inherited from the parents (due east.g., genes predisposing the adoptee to develop alcoholism). This information can be obtained from the records of the adoption agency, hospitals, social services, and similar sources. In studies of adoptees born out of marriage, reliable information well-nigh birth fathers oftentimes is lacking. However, contempo laws requiring written permission from biological fathers to release children for adoption may better data collection. For case, if a birth male parent'due south name is available, archival data from hospitalizations, incarcerations, or other records (due east.g., death certificates) can be obtained provided that the confidentiality required for such records tin can exist maintained.
Adoption agencies ordinarily can provide information well-nigh pregnancy and delivery (i.east., influences of the birth-parent environment). Similarly, bureau records can supply a large amount of personal data nearly the adoptive parents and the rearing environment. This information is specially of interest because adoption studies can mensurate the influences of specific ecology effects equally effectively as the influences of genetic effects. Information nigh the adoptees themselves also is readily available in near cases.
Ideally, adoption studies would include information obtained past personal interviews with all the people who primarily impact the adoptee's outcome (i.e., the birth parents, the adoptive parents, the adoptee, and friends of the adoptee). Information collected solely from institutional records, still, such equally those from the central registries in Scandinavian countries, also can provide valuable information and, at the very to the lowest degree, be used to identify subjects for directly study. Long-term followup of the adoptees, their birth parents, and their adoptive families would result in even more valid information near behaviors that tend to change over time, such as carry disorders, booze corruption, or low. Such longitudinal studies could considerably increase the identification of psychopathological behaviors that might go undetected in a study relying only on information gathered during one fourth dimension flow.
Proband Recruitment
How the probands are recruited also can impact the quality of a study'south conclusions. Ane potential source of bias is the influence of environmental factors on the selection of proband adoptees in the adoptees' family unit method. For example, psychological or social problems in an adoptive family may contribute to the adoptee'due south psychopathology. Simultaneously, these issues may prompt the family and the adoptee to seek more handling and thus increase their chances of beingness included in a sample of adoptees recruited from a clinic population. Factors such as these may compromise the representativeness of the sample.
Similarly, refusal rates amidst potential study participants could influence the quality of the data obtained. For example, information technology is possible that adoptees and their families who refuse to participate in a study as a group are distinguished by certain qualities (e.g., personality characteristics). Consequently, their refusal could reduce the representativeness of the written report sample.
Generalizability of Adoption Studies
Whether the findings from adoption studies tin be used to describe general conclusions about the contribution of both genetic and environmental factors to the development of alcoholism depends largely on how representative the adoptee sample is. Representativeness, in turn, is determined past variables, such as the criteria for proband pick. Although many of these variables can be controlled for or at least recognized, the inherent biases in adoption practices (e.g., selective placement and predominant recruitment of adoptive families from certain population groups) limit generalizability.
Summary
Despite the existing limitations and the technical issues associated with conducting adoption studies, the adoption paradigm provides important data most the significance of specific genetic and ecology factors in human beliefs. In improver, adoption studies allow researchers to identify specific genetic-environmental interactions that could be relevant for designing early interventions for behaviors that predispose a person to alcohol abuse and dependence.
Footnotes
aneFor a definition of this and other technical terms used in this article, run into central glossary, pp. 182–183.
twoAn odds ratio is a measure of association between two variables.
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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6875765/
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