Basics of
Epidemiology
Book list:
1. Epidemiology
By Leon Gordis (Elsevier Publication)
2. Park’s Textbook of Preventive and Social Medicine
By K Park
3. Introduction to Epidemiology
By Ray M. Merrill
4. Lecture Notes on Epidemiology
By Abdul Rashid Khan and K. A. Narayan
1
,2
,1. Introduction to Epidemiology
Epidemiology: The term epidemiology originates from the Greek terms epi (upon), demos (people) and logos (study)
that literally means the study of what is upon the people.
Epidemiology is the study of the frequency, distribution and determinants of diseases and other health related
conditions in human populations, and the application of this study to the promotion of health and to the prevention
and control of health problems.
Major components of the definition:
1. Population: The main focus of epidemiology is on the effect of disease on the population rather than
individuals. For example, malaria affects many people in Ethiopia but lung cancer is rare. If an individual
develops lung cancer, it is likely that, he/she will die. Even though lung cancer is more killer, epidemiology
gives more emphasis to malaria since it affects many people.
2. Frequency: This shows that epidemiology is mainly a quantitative science. Epidemiology is concerned with
the frequency (occurrence) of diseases and other health related conditions. Frequency of diseases is measured
by morbidity and mortality rates.
3. Distribution: Distribution refers to the geographical distribution of diseases, the distribution in time and
distribution by types of persons affected.
4. Determinants: Determinants are factors which determine whether or not a person will get a disease.
5. Health related conditions: Epidemiology is concerned not only with diseases but also with other health related
conditions because everything around us and what we do also affects our health. Health related conditions are
conditions which directly or indirectly affect or influence health. These may be injuries, births, health related
behaviors like smoking, unemployment, poverty etc.
Hi, Eva Come In and Complete Identification and Search
Uses of Epidemiology: The uses of epidemiology, as determined by Dr. Morris, a prominent British epidemiologist
are as follows:
1. Historical study: It studies whether community health is improving or declining.
2. Community diagnosis: Epidemiology studies what actual and potential health problems are there.
3. Evaluation of health services: This includes –
• Efficacy: Whether it works in an ideal setting or not.
• Effectiveness: Whether it works in the ‘real world’ or not and how it works.
• Efficiency: It can be measured by answering the question, how can the service utilize its resources for
maximum benefit?
4. Individual risks and chances: It includes –
• Actual risks
• Health hazards/risk appraisal
5. Completing the clinical picture: Different presentations of the disease.
6. Identification of syndromes: ‘Lumping and splitting’.
7. Search for causes: Case control and cohort studies.
8. Other uses: It includes –
• Evaluation of presenting signs and symptoms
• Clinical decision analysis.
Some of them are discussed below:
1. Historical study: Diseases and health events and behaviors can wax and wane over time in populations. For
example, new diseases appear (AIDS, SARS), some are eradicated (Small pox, polio in the Americas) and still
others are reduced to very low levels (mastoiditis, rheumatic fever).
• How is community health changing over time?
• Is it improving or declining?
3
, These can be decided only by selecting indicators and measuring diseases and health over time. This is one of
the basic responsibilities of any health system. Epidemiology has an important role to play in this process by
taking a historical perspective, documenting progression over time, looking at trends and being alert to new
developments.
2. Community diagnosis: Just as the clinical physician makes an assessment and diagnosis of the health of an
individual, public health workers, using the tools of epidemiology, assess and diagnose the health of a
community – a community diagnosis.
• How healthy is the population?
• Is its health getting better or worse?
• Are some areas or subgroups much healthier than others?
• How can we qualify these differences?
• What is the impact of ill health on society? How can we measure this?
• What are the population’s health needs?
• What risks does it face?
• What explains the differences in health?
Mortality (death) is an available indicator of the health of a community but this is a downstream measure
of population health.
Morbidity (sickness) is another measure of the health of a population but again, it has its limitations.
Epidemiology uses a number of more upstream indicators to assess the health of a population beyond
mortality and morbidity such as self-related, psychological well-being, activity limitation, life expectancy
and potential years of life lost (PYLL). The PYLL indicator is examined in detail in epidemiology.
3. Working of health services: Epidemiology can be used to assist public health practitioners in determining
whether health services are available, accessible, effective and efficient in meeting the population’s needs
identified in the community diagnosis.
• What percentage of the contacts of a case of multi-drug resistant tuberculosis have been located and
assessed?
• How many of the eligible children in a community are adequately immunized by school entry?
• How many are immunized on time, according to the recommended schedule?
• What proportion of restaurant workers has received adequate training in food handling?
• How often are supermarket meet coolers subjected to routine inspections?
• Are all women who become pregnant receiving antenatal care in the first trimester of their pregnancy?
4. Individual risks and chances: One might not realize it but can consider individual risks and chances in almost
everything one does – epidemiology is used everywhere, all of the time.
• What are the chances one will be alive five years from now?
• Is one going to start that exercise program today?
• Isn’t it time to make an appointment to have that Placental Alkaline Phosphatase (PAP) smear
repeated?
• One really should have an influenza shot again this year. What is her prognosis now that she has been
diagnosed with breast cancer?
• Should this group of newborns be followed closely because their birth weight was below 1500 grams?
These daily health related decisions are informed by the studies epidemiologists have undertaken in
populations to provide an assessment of the risk or chance of the occurrence of an event or illness.
Principles of epidemiology:
1. Defining a health problem.
2. Identifying risk factors associated with the problem.
3. Developing and testing community level interventions to control or prevent the cause of the problem.
4. Implementing interventions to improve the health of the population and
5. Monitoring those interventions to assess their effectiveness.
4
Epidemiology
Book list:
1. Epidemiology
By Leon Gordis (Elsevier Publication)
2. Park’s Textbook of Preventive and Social Medicine
By K Park
3. Introduction to Epidemiology
By Ray M. Merrill
4. Lecture Notes on Epidemiology
By Abdul Rashid Khan and K. A. Narayan
1
,2
,1. Introduction to Epidemiology
Epidemiology: The term epidemiology originates from the Greek terms epi (upon), demos (people) and logos (study)
that literally means the study of what is upon the people.
Epidemiology is the study of the frequency, distribution and determinants of diseases and other health related
conditions in human populations, and the application of this study to the promotion of health and to the prevention
and control of health problems.
Major components of the definition:
1. Population: The main focus of epidemiology is on the effect of disease on the population rather than
individuals. For example, malaria affects many people in Ethiopia but lung cancer is rare. If an individual
develops lung cancer, it is likely that, he/she will die. Even though lung cancer is more killer, epidemiology
gives more emphasis to malaria since it affects many people.
2. Frequency: This shows that epidemiology is mainly a quantitative science. Epidemiology is concerned with
the frequency (occurrence) of diseases and other health related conditions. Frequency of diseases is measured
by morbidity and mortality rates.
3. Distribution: Distribution refers to the geographical distribution of diseases, the distribution in time and
distribution by types of persons affected.
4. Determinants: Determinants are factors which determine whether or not a person will get a disease.
5. Health related conditions: Epidemiology is concerned not only with diseases but also with other health related
conditions because everything around us and what we do also affects our health. Health related conditions are
conditions which directly or indirectly affect or influence health. These may be injuries, births, health related
behaviors like smoking, unemployment, poverty etc.
Hi, Eva Come In and Complete Identification and Search
Uses of Epidemiology: The uses of epidemiology, as determined by Dr. Morris, a prominent British epidemiologist
are as follows:
1. Historical study: It studies whether community health is improving or declining.
2. Community diagnosis: Epidemiology studies what actual and potential health problems are there.
3. Evaluation of health services: This includes –
• Efficacy: Whether it works in an ideal setting or not.
• Effectiveness: Whether it works in the ‘real world’ or not and how it works.
• Efficiency: It can be measured by answering the question, how can the service utilize its resources for
maximum benefit?
4. Individual risks and chances: It includes –
• Actual risks
• Health hazards/risk appraisal
5. Completing the clinical picture: Different presentations of the disease.
6. Identification of syndromes: ‘Lumping and splitting’.
7. Search for causes: Case control and cohort studies.
8. Other uses: It includes –
• Evaluation of presenting signs and symptoms
• Clinical decision analysis.
Some of them are discussed below:
1. Historical study: Diseases and health events and behaviors can wax and wane over time in populations. For
example, new diseases appear (AIDS, SARS), some are eradicated (Small pox, polio in the Americas) and still
others are reduced to very low levels (mastoiditis, rheumatic fever).
• How is community health changing over time?
• Is it improving or declining?
3
, These can be decided only by selecting indicators and measuring diseases and health over time. This is one of
the basic responsibilities of any health system. Epidemiology has an important role to play in this process by
taking a historical perspective, documenting progression over time, looking at trends and being alert to new
developments.
2. Community diagnosis: Just as the clinical physician makes an assessment and diagnosis of the health of an
individual, public health workers, using the tools of epidemiology, assess and diagnose the health of a
community – a community diagnosis.
• How healthy is the population?
• Is its health getting better or worse?
• Are some areas or subgroups much healthier than others?
• How can we qualify these differences?
• What is the impact of ill health on society? How can we measure this?
• What are the population’s health needs?
• What risks does it face?
• What explains the differences in health?
Mortality (death) is an available indicator of the health of a community but this is a downstream measure
of population health.
Morbidity (sickness) is another measure of the health of a population but again, it has its limitations.
Epidemiology uses a number of more upstream indicators to assess the health of a population beyond
mortality and morbidity such as self-related, psychological well-being, activity limitation, life expectancy
and potential years of life lost (PYLL). The PYLL indicator is examined in detail in epidemiology.
3. Working of health services: Epidemiology can be used to assist public health practitioners in determining
whether health services are available, accessible, effective and efficient in meeting the population’s needs
identified in the community diagnosis.
• What percentage of the contacts of a case of multi-drug resistant tuberculosis have been located and
assessed?
• How many of the eligible children in a community are adequately immunized by school entry?
• How many are immunized on time, according to the recommended schedule?
• What proportion of restaurant workers has received adequate training in food handling?
• How often are supermarket meet coolers subjected to routine inspections?
• Are all women who become pregnant receiving antenatal care in the first trimester of their pregnancy?
4. Individual risks and chances: One might not realize it but can consider individual risks and chances in almost
everything one does – epidemiology is used everywhere, all of the time.
• What are the chances one will be alive five years from now?
• Is one going to start that exercise program today?
• Isn’t it time to make an appointment to have that Placental Alkaline Phosphatase (PAP) smear
repeated?
• One really should have an influenza shot again this year. What is her prognosis now that she has been
diagnosed with breast cancer?
• Should this group of newborns be followed closely because their birth weight was below 1500 grams?
These daily health related decisions are informed by the studies epidemiologists have undertaken in
populations to provide an assessment of the risk or chance of the occurrence of an event or illness.
Principles of epidemiology:
1. Defining a health problem.
2. Identifying risk factors associated with the problem.
3. Developing and testing community level interventions to control or prevent the cause of the problem.
4. Implementing interventions to improve the health of the population and
5. Monitoring those interventions to assess their effectiveness.
4
