Since CDC's inception, an important function of the agency has been the compilation, Analysis, and interpretation of statistical information to guide actions and policies to improve health. Sources of data include vital statistics records, medical records, personal interviews, telephone and mail surveys, physical examinations, and laboratory tTesting. Public health Surveillance data have been used to characterize the magnitude and distribution of illness and injury; to track health Trends; and to develop standard curves, such as growth charts. Beyond the development of appropriate program study designs and analytic methodologies, statisticians have played roles in the development of public health data-collection systems and software to analyze collected data. CDC/ATSDR employs approximately 330 mathematical and health statisticians. They work in each of the four coordinating centers, two coordinating offices, and the National Institute for Occupational Safety and Health.