Epidemiology is the study of the distribution and determinants of both disease and injury. Two triads are involved in epidemiology: (a) the agent, host, and environment triad and the time, place, and person triad. The primary goals of epidemiology are prevention, control, and, in rare instances, eradication disease and injury. Epidemiology started as a study of epidemics and extended to cover infectious disease and later non-infectious diseases. It has now become a methodological discipline that is used to study disease and non-disease phenomena.

CLASSIFICATION OF EPIDEMIOLOGY

Qualitative epidemiology deals with qualitative descriptions. Quantitative epidemiology deals with numerical descriptions. Observational epidemiology is based on observation of human phenomena. Experimental epidemiology involves assessment of the effects of intervention against a disease phenomenon. Theoretical epidemiology deals with mathematical and methodological issues. Descriptive epidemiology describes the patterns of disease occurrence in terms of place, time and person. Analytic epidemiology seeks to discover the underlying causes of diseases.

IMPORTANCE OF EPIDEMIOLOGY

Epidemiology is used in clinical medicine, public health, and actuarial sciences. The major activities of an epidemiologist are: study design including selection of the study sample, data collection, data analysis, data interpretation, and initiation of action programs to prevent disease and promote health. Professional practice and careers in Epidemiology are in government (Ministry of Health), universities, hospitals, and the private sector (drug manufacturers), and research institutes.

EPIDEMIOLOGIC METHODOLOGY:

An epidemiologic investigation proceeds through identifying and describing a problem, using the scientific method to formulate and test hypotheses, and interpreting findings. Epidemiological information is sourced from existing data or studies (observational or experimental). Existing data is from census, medical facilities, government, and private sector, health surveys, and vital statistics. Experimental studies, natural or true experiments, involve deliberate human action or intervention whose outcome is then observed. They have the advantage of controlled conditions but have ethical problems of experimenting on humans. Observational studies allow nature to take its course and just record the occurrences of disease and describe the what, where, when, and why of a disease. There are of 3 types of observational studies: cross-sectional, case control, and cohort (follow-up) studies. Their advantage is low cost and fewer ethical issues. They suffer from 3 disadvantages: disease aetiology is not studied directly because the investigator does not manipulate the exposures, unavailability of information, and confounding.

ETHICO-LEGAL ISSUES IN EPIDEMIOLOGY

A study involving humans must get approval from a recognized body. For approval the study must fulfill certain criteria. It must be scientifically valid. It is unethical to waste resources (time and money) on a study that will give invalid conclusions. Among ethical considerations are: individual vs. community rights, benefits vs. risks, informed consent, privacy and confidentiality, and conflict of interest. Epidemiologic study findings affect policy. Epidemiologists must know how to communicate risk to the public. It is an ethical obligation to report research findings to subjects so that they may take measures to lessen risk but care must be taken not to raise public anxiety without solid scientific evidence.