• Epidemiology (from the Greek epi = upon, and demos = people )
  
  Epidemiology is the medical discipline concerned with the distribution and determinants of a disease in a population evaluating the effects of many factors to determine personal, social and community characteristics of affected persons in comparison to those of non-affected persons. Epidemiology has been important as a source of ideas regarding the origin of diseases and as an approach for testing hypotheses of possible causation, taking advantage of remarkable advances in biology, including genetics, and in advanced statistical methodologies.
  
  
• Public Heath Statistics
  
  Public health statistics (vital statistics) monitor the health of populations by systematic counts of births and deaths, morbidity and disease outcomes in categories of patients by age, race, geography, socioeconomic status.
  
  
• Health Care Research
  
  Health care research determines access to general and specialized care, treatment efficiency and effectiveness with regard to subsets of the population specified by characteristics of the patients and characteristics of the available services.

For more information consult:

• Detels, Roger, et.al. Oxford Textbook of Public Health. 4th ed. Oxford ; New York : Oxford University Press, 2002.
  
  
• Labarthe, Darwin R. Epidemiology and Prevention of Cardiovascular Diseases : a global challenge. Gaithersburg, Md. : Aspen Publishers, 1998.
  
  
• Wallace, Robert B. ed. Maxcy-Roseneau-Last Public Health & Preventive Medicine. 14th ed. Stamford, Conn.: Appleton & Lange, c1998.
  
  
• Healthy People 2010 (Group). Healthy People 2010 : understanding and improving health. Washington, DC : U.S. Dept. of Health and Human Services, [2000].
  

Epidemiologic studies of birth defects are confronted with unique considerations arising from the complexity of embryonic maldevelopment. Disease expression may affect visible structural abnormalities as well as functional abnormalities, such as mental retardation, hearing loss, or biochemical alterations, such as hypothyroidism or phenylketonuria. This may present difficulties in crystallizing the focus of research and the appropriate classification of malformations. Most known causes of birth defects, such as maternal rubella or diabetes are expressed in a variety of manifestations, while each manifestation may also be due to a variety of other causes.

The disciplinary emphasis is on the comparison of individuals : exposed and unexposed to certain factors with respect to disease outcome; or those with the disease and those without with respect to familial and environmental circumstances.

Research Strategies

• Descriptive methods assess the public health importance of a disease and consider its occurrence, severity, variability, mortality and morbidity, cost and impact upon the community.
  
  
• Analytic studies make use of information on a variety of characteristics in affected and non-affected individuals and their families to derive hypotheses of possible causal or preventive significance.

To establish the significance of an association between a disease and certain candidate risk factors, the epidemiologic data must be examined in the light of experimental and clinical information on consistency, strength, temporal relationship, and coherence with biologic information.

Two major research designs of observational studies are defined by the way in which the comparison groups are identified :

• Case-control studies identify the comparison groups by disease status.
• Cohort studies identify the comparison groups by the presence or absence of a factor or 'exposure'.

Associations between factors and disease identified in observational studies must be evaluated in terms of three questions:

• Is the association due to chance ?
• Is the association due to bias in the study?
• Is the assocation due to confounding?
  

For rare conditions such as birth defects, the case-control approach is most appropriate to generate hypotheses regarding potential causal factors, each one of which may then be investigated in specific cohort designs.

For more information consult:

• Ferencz, C. Correa-Villasenor, A. Overview: The Epidemiologic Approach to the Study of Congenital Cardiovascular Malformations. In Clark EB, Markwald RR, Takao, A. (eds) Developmental Mechanisms of Heart Disease. Armonk, NY : Futura Pub.; pp. 629 - 638.