Epidemiology: An Introduction and Applications Social Pharmacy Notes

Epidemiology is the study of the distribution and determinants of health-related events and diseases in the population and also the application of this knowledge to control health problems. 

Earlier epidemiology was concerned with the study of epidemics and modern epidemiology deals with all diseases (whether acute or chronic, communicable or non-communicable) and health-related events and states occurring in man.

The three important components are: 1) Studies of disease frequency.
                                                            2) Studies of distribution of disease 
                                                            3) studies of the determinants of the disease.
There are three components of epidemiology which are frequency, distribution and determinants. Each of which conveys an important message and are described below.

Disease frequency
It is the measure of rate or ratio for e.g. Death rate.
This compares the frequency in different populations or subgroups.
It also involves the measurement of health-related events like height, weight, blood pressure etc.

Distribution of disease
It is not uniform but it occurs in certain patterns. Which varies in relation to a person, population, place and time. The incidence of which may be high in some areas and less in others. The same applies to time and this analysis helps in identifying risk factors. This aspect of epidemiology is also known as “descriptive epidemiology”.

Determinants of disease
This feature helps in identifying the risk factors and helps in the formulation of health programs, interventions and policies. It basically deals with the testing of etiological hypotheses and identification of underlying causes of risk factors of disease. It is described as” analytical epidemiology”.

This requires the application of epidemiological principles and methods.

To describe the size and distribution of disease problems in human populations.
To identify the etiological factors in the pathogenesis of the disease.
To provide the data essential for planning, implementation, and evaluation of services for the prevention, control and treatment of disease and for setting the priority amongst the services. 

Quantitative epidemiology 
Descriptive epidemiology
Analytical epidemiology 
Experimental (or intervention) epidemiology 

Study of the history of population and their disease trends :
To study the health history of the population and their disease trends which helps in identifying health problems.
Example: As the old diseases are eradicated (polio) new ones are identified (COVID- 19).so here epidemiological studies provide a means to study the disease profile and thus identify the health problems of the future.

Community diagnosis:
To arrive at community diagnosis.it comprises identification and quantification of health problems in a community in terms of mortality and morbidity rates and ratios   This is necessary for initiating preventive and control measures. as well as it serves as an indicator for the evaluation of health services retrospectively and provides knowledge about the disease distribution causation and prevention. 

Planning and evaluation :
To plan and evaluate health services. Here epidemiological studies about the distribution of health problems over time and place provide a fundamental basis for planning and developing the health services required for a community.

Evaluation of Individual’s risk:
Evaluation of risk and chances of a single individual evaluation study helps in the prediction of the degree of risk in a population. Any causal association between risk factors and disease can evaluate individual risk and chances.
 e.g. risk of bearing a mangol child, a risk to smokers of developing lung cancer and hypertensive patients for developing congestive heart failure.

Search for the risk factors:   
Searching for cause and risk factors herein epidemiology has made a significant contribution by searching and establishing the causes and risk factors involved in the etiology of many chronic and acute diseases. 
e.g. smoking as a cause of lung cancer 

Identification of disease syndrome
A number of medical syndromes with individual people have been identified by frequently associated findings e.g. association of iron deficiency anaemia and Patterson. Kelley syndrome.