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2.4: Descriptive and Epidemiological Research

  • Page ID
    221617
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    Learning Objectives
    • Describe how archival, longitudinal, cross-sectional, and epidemiological research are valuable to abnormal psychology
    • Differentiate between prevalence and incidence
    Other types of descriptive research include archival research, longitudinal and cross-sectional studies, and epidemiological studies.

    Longitudinal and Cross-Sectional Research

    Sometimes we want to see how people change over time. When we test the same group of individuals repeatedly over an extended period of time, we are conducting longitudinal research. Longitudinal research is a research design in which data-gathering is administered repeatedly over an extended period of time. For example, we may survey a group of individuals about their dietary habits at age 20; retest them a decade later at age 30; and then again at ages 40, 50, and 60 to possibly find correlations between diet and early-onset dementia. In this case, the longitudinal design is used to uncover risk factors of certain diseases, like Alzheimer’s. Longitudinal studies are also used in social-personality and clinical psychology to study rapid fluctuations in behaviors, thoughts, and emotions from moment to moment or day to day.

    Another approach is cross-sectional research. In cross-sectional research, a researcher compares multiple segments of the population at the same time. Using the dietary habits example above, the researcher might directly compare different groups of people by age. Instead of observing a group of people for 20 years to see how their dietary habits changed from decade to decade, the researcher would study a group of 20-year-old individuals and compare them to a group of 30-year-old individuals and then to a group of 40-year-old individuals, and so on. While cross-sectional research requires a shorter-term investment, it is also limited by differences that exist between the different generations (or cohorts) that have nothing to do with age per se, but rather reflect the social and cultural experiences of different generations of individuals that make them different from one another.

    In twin studies, researchers identify individuals with a specific disorder who are members of an MZ (monozygotic or identical) or a DZ (dizygotic or fraternal) twin pair and then study the other twin in the pairs. The Minnesota Twin Family Study is a twin study established in June 1989 with 1,300 same-gendered twin pairs ages 11 or 17, with an additional cohort of 500 such pairs recruited around 2004. Twins were born between 1972 and 2000. All twins born in Minnesota at that time were eligible to participate using birth registry data. Both identical and fraternal twins share certain aspects of their environment. This allows researchers to estimate the relative impact of environmental and genetic influences on phenotypes, an individual’s observable or expressed traits. The focus of the Minnesota Twin Family Study (MTFS) is on behavioral phenotypes, such as academic outcomes, cognitive abilities, personality, and interests; family and social relationships; mental and physical health; physiological measurements.

    1024px-Autosomal_Dominant_Pedigree_Chart2.svg_.png
    Figure \(\PageIndex{2}\): Pedigree chart showing an inheritance pattern consistent with autosomal dominant transmission. Behavioral geneticists have used pedigree studies to investigate the genetic and environmental basis of behavior.

    As with any research strategy, longitudinal research is not without limitations. For one, these studies require an incredible time investment by the researcher and research participants. Given that some longitudinal studies take years, if not decades, to complete, the results will not be known for a considerable period of time. In addition to the time demands, these studies also require a substantial financial investment. Many researchers are unable to commit the resources necessary to see a longitudinal project through to the end.

    Research participants must also be willing to continue their participation for an extended period of time, and this commitment can be problematic. People move, get married and take new names, get ill, and eventually die. Even without significant life changes, some people may simply choose to discontinue their participation in the project. As a result, the attrition rates, or reduction in the number of research participants due to dropouts, in longitudinal studies are quite high and increase over the course of a project. For this reason, researchers using this approach typically recruit many participants fully expecting that a substantial number will drop out before the end. As the study progresses, they continually check whether the sample still represents the larger population and make adjustments as necessary.

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    Epidemiological Studies

    The epidemiological method examines rates of occurrence of abnormal behavior in the population as a whole and in various subgroups classified according to factors such as race, ethnicity, gender, or social class. One type of epidemiological study is the survey method, which is used to discover rates of occurrence of various disorders. Often, occurrence of a single disease entity is set as an event. The events can be characterized by incidence rates (the number of new cases occurring during a specific period of time) and prevalence rates (the overall number of cases of a disorder existing in the population during a given period of time). Prevalence rates, then, include both new and continuing cases.

    1024px-SAMHSA.jpg
    Figure \(\PageIndex{3}\): The United States Substance Abuse and Mental Health Services Administration (SAMHSA) collects and reports on the epidemiology of mental disorders.

    The Substance Abuse and Mental Health Services Administration of the U.S. government (SAMHSA) is charged with improving the quality and availability of treatment and rehabilitative services in order to reduce illness, death, disability, and the cost to society resulting from substance abuse and mental illnesses. Surveys are conducted yearly to establish the frequency of use of illegal substances within the population. The World Health Survey was implemented by WHO in 2002–2004 in partnership with 70 countries to generate information on the health of adult populations, including psychological disorders and health systems. The total sample size in these cross-sectional studies includes over 300,000 individuals. These surveys provide valuable epidemiological data. We will rely upon and report about some of this epidemiological data when we learn about specific mental disorders.

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    Glossary

    adoption studies: studies that compare the trait and behavior similarity between an adoptee and his or her biological versus adoptive relatives

    attrition: reduction in number of research participants as some drop out of the study over time

    cohort: a group of people who share a defining characteristic, typically who experienced a common event in a selected period, such as birth or graduation

    cross-sectional research: compares multiple segments of a population at a single time

    incidence: the number of new cases occurring during a specific period of time

    longitudinal research: studies in which the same group of individuals is surveyed or measured repeatedly over an extended period of time

    phenotypes: an individual’s observable or expressed traits

    prevalence: the overall number of cases of a disorder existing in the population during a given period of time

    twin study: study in which researchers identify individuals with a specific disorder who are members of an MZ or a DZ twin pair and then study the other twin in the pairs


    1. Hidaka B. H. (2012). Depression as a disease of modernity: explanations for increasing prevalence. Journal of affective disorders, 140(3), 205–214. https://doi.org/10.1016/j.jad.2011.12.036
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