Descriptive Epidemiology

Descriptive Epidemiology

• Characterizes the amount and distribution of health and disease within a population

• Health outcomes are classified according to the variables of person, place, and time

• Person: sex, age, race/ethnicity

• Place: city, state, country

• Time: decade, year, month

Why use descriptive epidemiology?

• Evaluate trends in health and diseases

• Basis for creating, planning, providing, and evaluating health services/interventions

• Identifies problems to be further studied by analytic methods as well as areas fruitful for investigation

Descriptive epidemiology sets the stage for future investigations

• Such investigations include:

  • Evaluating observed trends

  • Planning for needed services

  • Launching more complex research

Types of descriptive epidemiologic studies

• case reports

• case series

• cross-sectional

Case reports

• accounts of a single occurence of a noteworthy health-related incident or small collection of such events

• highlight the need for investigations by public health authorities, enforcement of public health laws and practicies, and in-depth epidemiologic research

• EXAMPLES:

  • Bison encounters in Yellowstone National Park

  • Adverse reactions due to cosmetic surgery in the US

  • Imported rabid dogs

Case series

• Larger collection of cases of diseases, often grouped consecutively and listing common features such as the characteristics of affected patients

• EXAMPLE:

  • Reported cases of primary meningoencephalitis (121 cases between 1937 and 2007)

    • Primary exposure source: fresh water in lakes and rivers

Cross-sectional study

• Examines the relationship between diseases (or other health outcomes) and other variables of interest as the exist in a defined population at one particular time

• Prevalence study in which exposures and distributions of disease are determined at the same time

Epidemiologic inferences from descriptive data

• Descriptive epi and descriptive studies provide a basis for generating hypotheses

• We’re not able to make inferences from descriptive studies, but we can gather information to help guide our analytic studies

Good chart to review:

Socioeconomic status

• Descriptive term for a person’s position in society

• Often formulated as a composite measure of:

  • Income level

  • Education level

  • Type of occupation

• A single dimension of SES (ex. poverty level) may be used

• The social class gradient

  • Strong, inverse association of SES with levels of morbidity and mortality

  • Those in the lowest SES positions are confronted with excesses of morbidity and mortality from numerous causes

Health disparities

• difference in the occurrence of diseases and adverse health conditions in the population

  • African americans (in comparison to other groups) have the highest age-adjusted overall cancer incidence and death rates

  • WHY?— now, we insert hypothesis-driven research (analytic epidemiology)

International differences

• Differences may be attributed to climate, cultural factors, national dietary habits, access to health care

• example: variations in life expectancy (US ranked number 42 in 2014)

National differences

• Demonstrate within country variations in disease frequency

• Regional differences such as climate, latitude, and environmental pollution affect the prevalence and incidence of diseases

Urban-Rural difference

• demonstrates variations in morbidity and mortality related to environmental and lifestyle issues

Localized patterns of disease

• Diseases associated w/ specific environmental conditions that may exist in a particular geographic area

Secular trends

• gradual changes in disease or health conditions over long periods of time

• EXample:

  • Annual suicide rates between 1999 to 2012 among males and females aged 10-24 years

Cyclic (seasonal) trends

• increases and decreases in the frequency of a disease or other phenomenon over a period of several years or within one year

Point epidemics

• may indicate the response of a group of people in the same place with a common source of infection, contamination, or another etiologic factor to which they were exposed almost simultaneously

Clustering

• closely grouped series of events or cases of a disease or other health-related phenomena with well-defined distribution patterns in relation to time and/or place

• may suggest a common exposure

Temporal clustering

• health events that are related in time

• example:

  • development of maternal post-partum depression a few days after giving birth

Spatial clustering

• health events that occur in a specific geographic area

• example:

  • cancer cluster surrounding a source of toxic gas

Descriptive epi classifies

the occurrence of disease according to the variables of person, place, and time

Descriptive epi studies aid in

generating hypotheses that can be explored by analytic epidemiologic studies

What is epidemiologic inference?

• The process of inferring causes and effects from patterns of health and disease in defined populations