EPIDEMIOLOGY AND PUBLIC HEALTH
INTRODUCTION
DEFINITIONS
Epidemiology: is a method of reasoning about disease that deals with biological inference derived
from observations of disease phenomena in population groups".
Often considered the core science of public health, epidemiology involves “the study
of the distribution and determinants of disease frequency”
SCIENTIFIC RESEARCH
Scientific research intends to fill the gaps in knowledge or improve current knowledge with a final
goal of improving society. Epidemiologic research has a final goal of improving public health.
RESEARCH
Main strength: assessment of disease burden or the relationship (association) between
exposure and disease a population of interest
Method: counting withing groups and comparing
Main challenges:
- Who to count?
- When to count?
- How to compare?
Three main questions:
1. What is the burden of disease?
2. What is the prognosis of a disease?
3. Which are the risk factors/exposures causing a disease?
Three main ways to answer them:
1. Descriptive epidemiology: non-causal analyses which describe observed data (e.g.
surveillance)
- Very important for the base data
2. Predictive (prognosis) epidemiology: use of observed data to make statements or
predictions (e.g. used in clinical epidemiology).
3. Causal (etiologic) epidemiology: causal effects of risk factors/exposures on disease.
2+3 are analytical
1
, ROLE OF PUBLIC HEALTH
Establish health objectives and priorities
Health promotion
Disease prevention
Health protection
Health services
EPIDEMIOLOGY PURPOSES IN PUBLIC HEALTH
Discover the agent, host, and environmental factors that affect health
Determine the relative importance of causes of illness, disability, and death
Identify those segments of the population that have the greatest risk from specific causes of
ill health
Evaluate the effectiveness of health programs and services in improving population health
WHAT IS PUBLIC HEALTH?
Surveillance: descriptive epidemiology to establish objectives and priorities
Health services: planning & evaluation of health care services
Disease prevention:
- Primary prevention: intervening before health effects occur, through measures such as
vaccinations, altering risky behaviors (poor eating habits, tobacco use), and banning
substances known to be associated with a disease or health condition.
- Secondary prevention: screening to identify diseases in the earliest stages, before the
onset of signs and symptoms, through measures such as mammography and regular
blood pressure testing.
- Tertiary prevention: managing disease post diagnosis to slow or stop disease
progression through measures such as chemotherapy, rehabilitation, and screening for
complications.
2
, Health promotion: health promotion enables people to increase control over their own
health. It covers a wide range of social and environmental interventions that are designed to
benefit and protect individual people’s health and quality of life by addressing and
preventing the root causes of ill health, not just focusing on treatment and cure.
Health protection: minimization of the exposure to health hazards to protect the population
by ensuring environmental, occupational, toxicological and food safety.
HISTORY
Slides !!
3
, LECTURE 2: MEASURES OF OCCURRENCE
EPIDEMIOLOGICAL FRACTIONS
Proportion: x / N = x / (x + y)
Odds: x / (N-x) = x / y
Rate: x / N * 1 / t = x / (x+y) * t
- More useful to compare measurements
CONCEPTS
COHORT
= group of people usually followed through time
Closed cohort: start following everyone at the same time
Open cohort: not the same time slots for everyone some people are followed
longer/shorter than others
- People enter and leave at different times
PREVALENCE & INCIDENCE
Prevalence: description of population with existing disease in single point of time
Incidence: number of new events in a population in a defined period of time
PREVALENCE
Point prevalence: one time point or very short period of time (minutes, days)
Period prevalence: defined longer period of time (months, years)
Prevalence counts: absolute number of cases
- To communicate information
- Often lacks context
Prevalence proportion: n cases / total population
- when lower than 10%, the proportion & odds are close
- when its high, the prevalence odds overestimates the prevalence proportion
Prevalence odds: two ways to calculate this
- prevalence proportion / 1 – prevalence proportion
- n of cases / population – n of cases
They all combine incidence and duration
4
INTRODUCTION
DEFINITIONS
Epidemiology: is a method of reasoning about disease that deals with biological inference derived
from observations of disease phenomena in population groups".
Often considered the core science of public health, epidemiology involves “the study
of the distribution and determinants of disease frequency”
SCIENTIFIC RESEARCH
Scientific research intends to fill the gaps in knowledge or improve current knowledge with a final
goal of improving society. Epidemiologic research has a final goal of improving public health.
RESEARCH
Main strength: assessment of disease burden or the relationship (association) between
exposure and disease a population of interest
Method: counting withing groups and comparing
Main challenges:
- Who to count?
- When to count?
- How to compare?
Three main questions:
1. What is the burden of disease?
2. What is the prognosis of a disease?
3. Which are the risk factors/exposures causing a disease?
Three main ways to answer them:
1. Descriptive epidemiology: non-causal analyses which describe observed data (e.g.
surveillance)
- Very important for the base data
2. Predictive (prognosis) epidemiology: use of observed data to make statements or
predictions (e.g. used in clinical epidemiology).
3. Causal (etiologic) epidemiology: causal effects of risk factors/exposures on disease.
2+3 are analytical
1
, ROLE OF PUBLIC HEALTH
Establish health objectives and priorities
Health promotion
Disease prevention
Health protection
Health services
EPIDEMIOLOGY PURPOSES IN PUBLIC HEALTH
Discover the agent, host, and environmental factors that affect health
Determine the relative importance of causes of illness, disability, and death
Identify those segments of the population that have the greatest risk from specific causes of
ill health
Evaluate the effectiveness of health programs and services in improving population health
WHAT IS PUBLIC HEALTH?
Surveillance: descriptive epidemiology to establish objectives and priorities
Health services: planning & evaluation of health care services
Disease prevention:
- Primary prevention: intervening before health effects occur, through measures such as
vaccinations, altering risky behaviors (poor eating habits, tobacco use), and banning
substances known to be associated with a disease or health condition.
- Secondary prevention: screening to identify diseases in the earliest stages, before the
onset of signs and symptoms, through measures such as mammography and regular
blood pressure testing.
- Tertiary prevention: managing disease post diagnosis to slow or stop disease
progression through measures such as chemotherapy, rehabilitation, and screening for
complications.
2
, Health promotion: health promotion enables people to increase control over their own
health. It covers a wide range of social and environmental interventions that are designed to
benefit and protect individual people’s health and quality of life by addressing and
preventing the root causes of ill health, not just focusing on treatment and cure.
Health protection: minimization of the exposure to health hazards to protect the population
by ensuring environmental, occupational, toxicological and food safety.
HISTORY
Slides !!
3
, LECTURE 2: MEASURES OF OCCURRENCE
EPIDEMIOLOGICAL FRACTIONS
Proportion: x / N = x / (x + y)
Odds: x / (N-x) = x / y
Rate: x / N * 1 / t = x / (x+y) * t
- More useful to compare measurements
CONCEPTS
COHORT
= group of people usually followed through time
Closed cohort: start following everyone at the same time
Open cohort: not the same time slots for everyone some people are followed
longer/shorter than others
- People enter and leave at different times
PREVALENCE & INCIDENCE
Prevalence: description of population with existing disease in single point of time
Incidence: number of new events in a population in a defined period of time
PREVALENCE
Point prevalence: one time point or very short period of time (minutes, days)
Period prevalence: defined longer period of time (months, years)
Prevalence counts: absolute number of cases
- To communicate information
- Often lacks context
Prevalence proportion: n cases / total population
- when lower than 10%, the proportion & odds are close
- when its high, the prevalence odds overestimates the prevalence proportion
Prevalence odds: two ways to calculate this
- prevalence proportion / 1 – prevalence proportion
- n of cases / population – n of cases
They all combine incidence and duration
4
