D) Uses of Epidemiology 

Epidemiology has been defined as a "means of learning, or asking questions and getting answers that lead to further questions".
In this context, Morris identified seven distinct uses of epidemiology.

I ) To study historically the rise & fall of diseases in the population.

1. It is study of history of disease in human population.
2. Health and Disease Pattern in community is never constant, 
   There are Fluctuations over short and long periods of time.
3. First contribution of epidemiology to study of Coronary Heart Disease is labelling CAD as "epidemic".
4. Epidemiology provides means to study disease profiles & 
                                                                          time trends                    in human population.
5. By study of these trends we can make useful projections into the future &
                                                             identify emerging health problems and their correlates.

II ) Completing the natural history of disease.

1. Epidemiology is concerned with entire spectrum of disease in population.
   Epidemiologist can broadest perspective of disease as he is concerned with all cases in defined population,
   regardless of severity or source of medical care.
2. Epidemiologist studies disease pattern in community in relation to agent, host and environment factors & 
   Can better fill in gaps in natural history of disease.
3. Contribution of epidemiology to study of Atherosclerosis is that 1/3 to 1/2 deaths occur suddenly (in one hour) 
   which would not have shown on hospital studies as patients don't reach hospitals in time.
   This gave tremendous impetus to development of intensive coronary care units.
4. Epidemiological investigations have given large amount of data on risk factors in relation to chronic diseases.

III ) Community Diagnosis 

1.  Epidemiology is "diagnostic tool" of community medicine.
    Community Diagnosis includes population distributions and profiles of illness & 
    understanding of social, cultural and environmental characteristics of community.

IV ) Planning & Evaluation

1.  Planning is essential for rational allocation of limited resources.
    Application of epidemiological principles to problems of heath care is "new epidemiology".
2.  Example : Planning facilities for medical care ( no. of hospital beds for specific diseases patients, health manpower planning)
                                                             preventive services  (Immunisation campaigns, provision of sanitary services 
                       Planning for research
3. Evaluation : Any measures taken to control or prevent a disease must be followed by an evaluation to find out whether the measures undertaken are effective in reducing the frequency of the disease.
   Value of method in relation to others is assessed by cost effectiveness studies.
   Development of randomised controlled trial has made it possible to evaluate treatment modalities on firm scientific basis. 
4. It is not enough to know that a programme provides some benefit ; 
   We need to know how much benefit and at what risk and cost.        

V ) Evaluation of Individual's Risks & Chances 

Epidemiologists calculate measures of

1. Absolute Risk : Incidence Rate 
                              Specific Rates
2.  Relative Risk and Attributable Risk for a factor related to or
                                                                                      believed to be        cause of disease.
3. Example : Risk of bearing a Mongol child and of some hereditary diseases.
                     Risk assessment for smokers and non smokers for selected causes of disease. 

VI ) Searching for Causes & Risk Factors 

1. Epidemiology tries to identify cause of disease by 
   Relating disease to
   Inter population differences and other attributes of population or cohorts examined
2. Examples : Identification of 
   Rubella as cause of congenital defects 
   Thalidomide as teratogenic agents
   Cigarette smoking as cause of lung cancer
3. In case of chronic diseases, concept of "Risk Factors" gave renewed impetus to epidemiological research.

VII ) Syndrome Identification

1. Epidemiological investigations can be used to define and refine medical syndromes 
   That are identified by observing frequently associated findings in individual patients.
2. Example : Differentiation of gastric and duodenal ulcer was through
                     "poverty" gradient in gastric ulcer  = Present
                                                           duodenal ulcer = Absent