What is epidemiology and why is it important?

115.4 percent of American adults have a serious mental  illness" (Kessler et ol., 1998)

"Suicide is the 2nd leading cause of death among men 25-34 in the United States" (Centers for Disease Contro!,2014)

"Serious mental illnesses cost society $193.2 billion in lost earnings per year" (Kessler et al., 2008)

"Mental and behavioral disorders, such as depression, anxiety, and drug use, are the primary drivers of disability worldwide and caused over 40 million years of disability in 20- to 29- year-olds" (WHO Organization, 2004)

Broadly speaking, epidemiology is the study of health and illness in human populations (Kleinbaum, Kupper & Morgenstern, 1982). More specifically, epidemiology can fall into two general areas. Descriptive epidemiological studies examine the incidence and prevalence of different health-related outcomes.

• Incidence rate: The rate at which new cases occur in a population during a specific period. For example:

- Missouri has the 18'h highest rate of suicide in the nation among youth 10-2-1 year o Ids. In 2013, the rate was 18 higher than the national average (9.6-1 compared to 8.15 per 100,000 nationally). (Centers for Disease Control and Prevention, 2013).

• Prevalence rate: The proportion of a case that exists in a population at a point in time (usually expressed by a percentage). For example:

- "5.4 of all American adults have a serious mental illness" (Kessler et al., 1998)

Descriptive epidemiology also examines the occurrence of a disease or health outcome for different populations, such as age, gender, race, culture, economic status, education, occupation, etc. Descriptive epidemiological questions might include:

1) What mental illnesses (including substance abuse) are most common in the U.S.? Internationally? Are there differences in the prevalence of these illnesses globally?

2) What mental illnesses are most common among children? Adolescents? The elderly?

3) What is the cost and burden of mental illness to society? Are there differences based upon the type of illness?

4) Do characteristics such as wealth, culture/race, occupation or education affect a person's mental health?

Analytic epidemiological studies explore the relationship between risk factors and antecedent conditions to health outcomes. These studies might examine the effects of parenting, school achievement, alcohol and drug use, exposure to trauma, genetics, religious upbringing or a host of other factors on a mental health outcome. These studies can be used to identify risk factors and assess the relative strength of association of each of these risk factors to the mental health outcome of interest (also called correlational
research).

Examples of conclusions that might be reached as a result of an analytic epidemiological study might include:

1) Positive teacher-student relationships are strongly correlated with low substance use among adolescents (Missouri Student Survey. 2014)

2) Prior suicide attempts are among the strongest risk factors for completed suicide" (Moscicki, 1997)

3) Maternal prenatal poverty may be a risk factor for schizophrenia (Cohen, 1993).

Questions to be answered in an analytic epidemiological study might include:

1) Are some mental illnesses inherited? Environmentally related? Induced by stress?

2) What is the impact of war on mental health? What is the impact of natural disasters on mental health?

3) Is mental health stigma more prevalent within certain demographic groups?

4) What risk factors are related to suicide? Are there different risk factors for those who attempt suicide compared to those who complete suicide?

5) Are some people more resilient than others in their ability to resist using alcohol or other drugs? What characteristics make them more resilient?

6) Is there a relationship between schizophrenia and violence?

Altogether, information from epidemiological studies can be used to understand the burden of disease and its associated costs, assess the health needs of particular populations, advocate and provide treatment to populations most at risk, develop health-care policies and allocate resources.