Abnormal Psychology. William J. Ray

disadvantage of these designs is that they require a significant period of time to complete the study.

      Epidemiological Research

      Epidemiology is the study of the distribution and determinants of the frequency of a disorder in humans (see Tsuang, Cohen, & Jones, 2011, for an overview). Within psychopathology, epidemiological approaches have been used to determine how frequently a particular disorder is present in men or women and if a particular disorder is related to other factors such as income or level of industrialization of a country.

      epidemiology: the study of the distribution and determinants of the frequency of a disorder in humans

      Epidemiological research is particularly helpful in determining the nature, etiology, and prognosis of a given disorder. From this type of research, we know that autism begins early in life and continues throughout one’s lifetime. Anxiety disorders, on the other hand, can begin in adolescence, but by early adulthood, a number of individuals who experienced one or more of these in adolescence will no longer experience the disorder. We also know that schizophrenia is seen in similar percentages throughout the world.

      prevalence: the proportion of individuals who have a particular disorder at a particular time period

      There are a variety of measures used in epidemiological research to describe the statistical profile of psychological disorders. One common measure is prevalence, which is the proportion of individuals who have a particular disorder at a particular time period. If you go to the National Institute of Mental Health (NIMH) website—http://www.nimh.nih.gov/statistics/index.shtml—you can see the prevalence rates for the major disorders from the Diagnostic and Statistical Manual of Mental Disorders (DSM). For example, you will see that the 12-month prevalence for general anxiety disorder (GAD) in adults is 3.1%. What this means is that 3.1% of the U.S. population during a 12-month period had the disorder. Another type of prevalence is referred to as lifetime prevalence. This is the percentage of a specific population that had the disorder at some point in their life, even if they no longer show symptoms of the disorder currently. As would be expected, lifetime prevalence is always larger than the number of individuals who have the disorder during a given 12-month period. In the case of GAD, lifetime prevalence is 5.7%. Further types of epidemiology data can include prevalence rates of the disorder in terms of specific factors such as gender, age, or average age at onset of the disorder. These data are shown for GAD in Figure 3.11.

      lifetime prevalence: the percentage of a specific population that had the disorder at some point in their life, even if they no longer show symptoms of the disorder currently

      Epidemiological studies also allow us to look at particular populations. For example, we could ask what percentage of individuals in prison has a mental disorder. These data were collected in 2002 and 2004 and are shown in Figure 3.12. From this graph, it can be seen that there are higher rates of inmates with mental disorders in local as compared with federal prisons. Although not shown in the graph, in the United States, there are now more than 3 times more seriously mentally ill individuals in jails and prisons than in hospitals (Torrey, Kennard, Eslinger, Lamb, & Pavle, 2010).

      Figure 3.11 How Many People in the United States Experience Anxiety?

      Source: NIH (2005), http://www.nimh.nih.gov/health/statistics/prevalence/generalized-anxiety-disorder-among-adults.shtml

      Another epidemiological measure is incidence, which refers to the number of new cases of a disorder that develop during a certain period of time. Another way of thinking about incidence is to describe it as risk. That is, what is the risk of someone in a specific population developing the disorder in a given time period?

      Figure 3.12 What Percentage of Inmates Have Mental Health Problems?

      Source: NIH, http://www.nimh.nih.gov/health/statistics/prevalence/inmate-mental-health.shtml

      Risk is also considered in a statistical manner in terms of correlation or association. For example, you can ask if there is a relationship between environmental variables such as abuse in childhood and development of a particular disorder such as depression. Subject variables such as gender are also used in this way. For example, 1 in 4 females and 1 in 10 males will have depression in their lifetime. Thus, there is a greater risk factor for females as compared with males in terms of developing depression. As with all measures of association, the presence of a relationship does not imply causation.

      Research Involving Genetics

      Traditional genetics studies have sought to determine which aspects of a person’s behavior can be attributed to genetic factors and which can be said to be related to environmental factors. Early research sought to find the single gene or genes involved in psychological disorders such as schizophrenia. However, with continued progress in understanding the approximately 20,000 genes of humans and the role of epigenetic factors in turning genes on and off, the picture has become much more complicated than previously thought.

      incidence: the number of new cases of a disorder that develop during a certain period of time

      risk: related to incidence, the likelihood that someone in a specific population will develop a particular disorder in a given time period

      This has led scientists to search for endophenotypes (see Chapter 2), which lie between the genotype and the phenotype. For example, when we think about schizophrenia, we most often think in terms of the phenotypes including hearing voices and having delusions. However, endophenotypes involving cognitive and memory problems are an important part of schizophrenia (Barch & Ceaser, 2012), and are found in both individuals with schizophrenia and, often in nonclinical manifestations, in their first-degree relatives. Both cognitive and emotional-related endophenotypes are seen in other disorders.

      Behavioral Genetics

      One type of genetics research involving psychopathology is behavioral genetics, which is the study of genetic and environmental contributions to organisms’ behavior (see G. Carey, 2003; DiLalla, 2004; Kendler, Jaffee, & Romer, 2011; Plomin, DeFries, Knopik, & Neiderhiser, 2012, for overviews). One large question is the manner in which genes and the environment work together to shape behavior. Researchers use a variety of behavioral genetic approaches to quantify the amount of variance, which can be attributed to genetic and environmental influences.

      behavioral genetics: the study of genetic and environmental contributions to organisms’ behavior

      gene by environment interaction: the possibility that individuals with different genotypes may respond to the same environment in different ways

      One traditional distinction has been between gene by environment interaction as opposed to gene by environment correlations (Plomin, DeFries, & Loehlin, 1977). Gene by environment interactions refer to the possibility that individuals with different genotypes may respond to the same environment in different ways. For example, some children respond to stress differently from others based on their genotype. As noted, mistreatment as a child influenced some boys differently from others later in adulthood (Caspi et al., 2002). Those boys who were mistreated in childhood and had a particular form of the MAOA gene were more likely to be violent and engage in a variety of antisocial behaviors as adults.

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