This document discusses various epidemiological measures used to describe the frequency and distribution of health events in populations. It describes counts, ratios, proportions, and rates. Counts refer to the simple number of cases. Ratios, proportions, and rates relate the number of cases to the population size. Proportions express the number of cases as a percentage of the population. Rates relate the number of cases over time to population size. Incidence measures new cases over time while prevalence measures existing cases at a point in time. Relative and absolute measures are used to assess the strength of associations between exposures and health outcomes.
Frequency measures of health is an important aspect in the planing of the type of services required in a specific population. This is due to the fact that they are able to indicate the type and level of health problems being faced In that population during a specified period of time.
Chapter 3Measures of Morbidity and Mortality Used in .docxketurahhazelhurst
Chapter 3
Measures of Morbidity and
Mortality Used in
Epidemiology
Learning Objectives
• Define and distinguish among ratios,
proportions, and rates
• Explain the term population at risk
• Identify and calculate commonly used
rates for morbidity, mortality, and natality
• State the meanings and applications of
incidence rates and prevalence
Learning Objectives (cont’d)
• Discuss limitations of crude rates and
alternative measures for crude rates
• Apply direct and indirect methods to
adjust rates
• List situations where direct and indirect
adjustment should be used
Overview of Epidemiologic
Measures
Count
• The simplest and most frequently
performed quantitative measure in
epidemiology.
• Refers to the number of cases of a
disease or other health phenomenon
being studied.
Examples of Counts
• Cases of influenza reported in
Westchester County, New York,
during January of a particular year.
• Traffic fatalities in Manhattan in a 24-
hour time period
• College dorm students who had mono
• Foreign-born stomach cancer patients
Ratio
• The value obtained by dividing one
quantity by another.
• Consists of a numerator and a
denominator.
• The most general form has no specified
relationship between numerator and
denominator.
• Rates, proportions, and percentages are
also ratios.
Example of a
Simple Sex Ratio Calculation
• A ratio may be expressed at = X/Y
• Simple sex ratio (data from textbook)
• Of 1,000 motorcycle fatalities, 950 victims
are men and 50 are women.
Number of male cases 950
Number of female cases 50
19:1 male to female= =
Example of a
Demographic Sex Ratio Calculation
• This ratio refers to the number of
males per 100 females. In the U.S.,
the sex ratio in 2010 for the entire
population was 96.7, indicating more
females than males.
Number of male cases 151,781,326
Number of female cases 156,964,212
96.7X 100 = =X 100
Example of a
Sex Ratio at Birth Calculation
• The sex ratio at birth is defined as:
(the number of male births divided by
the number of female births)
multiplied by 1,000.
Number of male births
Number of female births
X 1,000
Definition of Proportion
• A measure that states a count relative
to the size of the group.
• A ratio in which the numerator is part
of the denominator.
• May be expressed as a percentage.
Uses of Proportions
• Can demonstrate the magnitude of a
problem.
• Example: 10 dormitory students
develop hepatitis. How important is
this problem?
– If only 20 students live in the dorm, 50%
are ill.
– If 500 students live in the dorm, 2% are
ill.
Example of a Proportion
• Calculate the proportion of African-
American male deaths among African-
American and white boys aged 5 to 14
years.
Rate
• Definition: a ratio that consists of a
numerator and a denominator and in
which time forms part of the denominat ...
Case reports and case series are descriptive studies that provide initial clues about new diseases or exposures. A case report describes the experience of a single patient, while a case series describes the experiences of multiple patients with similar characteristics. These study designs are useful for generating hypotheses, but have limitations due to lack of controls and small sample sizes. Ecological studies examine the relationship between disease rates and other population characteristics using aggregate data. They are useful for initial hypothesis generation but cannot prove causation. Cross-sectional studies measure exposure and outcome simultaneously in a population. They provide a snapshot of disease occurrence and can identify risk factors, but cannot determine temporal relationships.
The prevalence rate as of June 30, 2012 is the number of active TB cases on that date (264) divided by the population on March 30, 2012 (183,000) and multiplied by 100,000.
264/183,000 = 144 per 100,000
The answer is c.
mudule 3 Measure of health and Health Related Events.pdfteddiyfentaw
This document discusses various measures used to quantify health and disease in populations. It begins by defining key concepts like ratios, proportions, and rates. It then examines measures of morbidity like incidence rate and prevalence. Measures of mortality such as case-fatality rate and proportionate mortality ratio are also introduced. The document concludes by explaining measures of association between exposure and disease, including relative risk, odds ratio, and impact measures like attributable risk.
This document provides information on key epidemiological measurements and concepts. It defines epidemiology as the study of health-related states and events in populations. The objectives are to learn measurements in epidemiology including rates, ratios and proportions. It discusses various types of rates like crude, specific and standardized rates. It also covers measurements of mortality like crude death rate, specific death rate and case fatality rate. For morbidity, it explains incidence, prevalence, and their relationship. Incidence measures new cases while prevalence includes old and new cases at a point in time. Overall, the document outlines fundamental epidemiological terms and calculations.
This document discusses incidence, a measure used in epidemiology to describe the occurrence of new cases of a disease in a population over time. It defines incidence proportion as the proportion of individuals who develop a disease during a specified period. Incidence rate is described as a rate that incorporates time at risk in the denominator and represents the number of new cases per unit of time. Examples are provided to demonstrate how to calculate both incidence proportion and incidence rate.
Frequency measures of health is an important aspect in the planing of the type of services required in a specific population. This is due to the fact that they are able to indicate the type and level of health problems being faced In that population during a specified period of time.
Chapter 3Measures of Morbidity and Mortality Used in .docxketurahhazelhurst
Chapter 3
Measures of Morbidity and
Mortality Used in
Epidemiology
Learning Objectives
• Define and distinguish among ratios,
proportions, and rates
• Explain the term population at risk
• Identify and calculate commonly used
rates for morbidity, mortality, and natality
• State the meanings and applications of
incidence rates and prevalence
Learning Objectives (cont’d)
• Discuss limitations of crude rates and
alternative measures for crude rates
• Apply direct and indirect methods to
adjust rates
• List situations where direct and indirect
adjustment should be used
Overview of Epidemiologic
Measures
Count
• The simplest and most frequently
performed quantitative measure in
epidemiology.
• Refers to the number of cases of a
disease or other health phenomenon
being studied.
Examples of Counts
• Cases of influenza reported in
Westchester County, New York,
during January of a particular year.
• Traffic fatalities in Manhattan in a 24-
hour time period
• College dorm students who had mono
• Foreign-born stomach cancer patients
Ratio
• The value obtained by dividing one
quantity by another.
• Consists of a numerator and a
denominator.
• The most general form has no specified
relationship between numerator and
denominator.
• Rates, proportions, and percentages are
also ratios.
Example of a
Simple Sex Ratio Calculation
• A ratio may be expressed at = X/Y
• Simple sex ratio (data from textbook)
• Of 1,000 motorcycle fatalities, 950 victims
are men and 50 are women.
Number of male cases 950
Number of female cases 50
19:1 male to female= =
Example of a
Demographic Sex Ratio Calculation
• This ratio refers to the number of
males per 100 females. In the U.S.,
the sex ratio in 2010 for the entire
population was 96.7, indicating more
females than males.
Number of male cases 151,781,326
Number of female cases 156,964,212
96.7X 100 = =X 100
Example of a
Sex Ratio at Birth Calculation
• The sex ratio at birth is defined as:
(the number of male births divided by
the number of female births)
multiplied by 1,000.
Number of male births
Number of female births
X 1,000
Definition of Proportion
• A measure that states a count relative
to the size of the group.
• A ratio in which the numerator is part
of the denominator.
• May be expressed as a percentage.
Uses of Proportions
• Can demonstrate the magnitude of a
problem.
• Example: 10 dormitory students
develop hepatitis. How important is
this problem?
– If only 20 students live in the dorm, 50%
are ill.
– If 500 students live in the dorm, 2% are
ill.
Example of a Proportion
• Calculate the proportion of African-
American male deaths among African-
American and white boys aged 5 to 14
years.
Rate
• Definition: a ratio that consists of a
numerator and a denominator and in
which time forms part of the denominat ...
Case reports and case series are descriptive studies that provide initial clues about new diseases or exposures. A case report describes the experience of a single patient, while a case series describes the experiences of multiple patients with similar characteristics. These study designs are useful for generating hypotheses, but have limitations due to lack of controls and small sample sizes. Ecological studies examine the relationship between disease rates and other population characteristics using aggregate data. They are useful for initial hypothesis generation but cannot prove causation. Cross-sectional studies measure exposure and outcome simultaneously in a population. They provide a snapshot of disease occurrence and can identify risk factors, but cannot determine temporal relationships.
The prevalence rate as of June 30, 2012 is the number of active TB cases on that date (264) divided by the population on March 30, 2012 (183,000) and multiplied by 100,000.
264/183,000 = 144 per 100,000
The answer is c.
mudule 3 Measure of health and Health Related Events.pdfteddiyfentaw
This document discusses various measures used to quantify health and disease in populations. It begins by defining key concepts like ratios, proportions, and rates. It then examines measures of morbidity like incidence rate and prevalence. Measures of mortality such as case-fatality rate and proportionate mortality ratio are also introduced. The document concludes by explaining measures of association between exposure and disease, including relative risk, odds ratio, and impact measures like attributable risk.
This document provides information on key epidemiological measurements and concepts. It defines epidemiology as the study of health-related states and events in populations. The objectives are to learn measurements in epidemiology including rates, ratios and proportions. It discusses various types of rates like crude, specific and standardized rates. It also covers measurements of mortality like crude death rate, specific death rate and case fatality rate. For morbidity, it explains incidence, prevalence, and their relationship. Incidence measures new cases while prevalence includes old and new cases at a point in time. Overall, the document outlines fundamental epidemiological terms and calculations.
This document discusses incidence, a measure used in epidemiology to describe the occurrence of new cases of a disease in a population over time. It defines incidence proportion as the proportion of individuals who develop a disease during a specified period. Incidence rate is described as a rate that incorporates time at risk in the denominator and represents the number of new cases per unit of time. Examples are provided to demonstrate how to calculate both incidence proportion and incidence rate.
This document discusses key concepts in epidemiology including rates, ratios, incidence, prevalence, mortality, and morbidity. It defines these terms and provides examples of how to calculate different rates. Specifically, it explains how to calculate crude death rate, infant mortality rate, maternal mortality rate, and prevalence. These basic health indicators are important for measuring changes over time, analyzing health situations, determining the magnitude of health problems, and allowing meaningful comparisons.
Measurement of Epidemiology
Radha Maharjan
MN (WHD)
Contents
5.1 Morbidity
Incidence
Prevalence
Attack Rate
Contents
5.2 Mortality
Crude Death Rate
Case Fatality Rate
Proportional Mortality Rate
Survival Rate
Standardized Death Rate
Contents
5.3 Disability
Disability Adjusted Life Years (DALY)
Quality Adjusted Life Years (QALY)
5.4 Tools of Measurements
Rate
Ratio
Proportion
5.4 Tools of Measurements
Numerator
Numerator refer to the number of times an event (e.g. number of birth) has occurred in a population, during a specified time period.
Denominator
Numerator has little meaning unless it is related to the denominator. The epidemiologist has to choose an appropriate denominator while calculating a rate.
It may be related to:
(I) population
(II) the total events.
Denominator related to the population
Mid year population
Population at risk
Person – time
Sub groups of the population
Denominator related to the Total Events
Mid year population
The population size changes daily due to births, deaths and migration, the mid year population is commonly chosen as a denominator.
The population as on 1st July is mid-year population.
Population at risk
It is important to note that the calculation of measures of disease frequency depends on correct estimates of the numbers of people under consideration.
Ideally, these figures should include only those people who are potentially susceptible to the disease studied.
Population at risk
For instance, men should not be included in denominator for the carcinoma of cervix.
Part of population, which is susceptible to a disease is called the population at risk,
e.g., Occupational injuries occur only among working people so the population at risk is the workforce.
Person – time
In some epidemiological studies (e.g. cohort studies), person may enter into the study at different times.
Consequently, they are under observation for varying time period.
In such case, the denominator is a combination of person and time.
Person – time
The most frequently used person time is person- years.
Some times this may be person- months, person -weeks or man- hours.
For example, if 10 persons were observed in the study for 10 years, person time would be 100 person years of observation.
Person – time
The same figure would be derived if 100 persons were under observation for one year.
These denominators have the advantage of summarizing the experience of persons with different duration of observation or exposure.
Sub groups of the population
The denominator may be subgroups of population
e.g. under-five, female, doctors, etc.
Denominator related to the Total Events
In some instances, the denominator may be related to total events instead of the total population, as in the case of infant mortality rate the denominator is total number of live births.
Definition concept and comparison of ratio, proportion and rate.
MEASURES OF DISEASE FREQUENCY. ASSOSCIATION AND IMPACTAneesa K Ayoob
This document discusses various measures used to quantify disease frequency, association, and impact in epidemiology. It defines key terms like incidence, prevalence, risk, rate, and ratio. For measures of disease frequency, it distinguishes between incidence, which considers new cases over time, and prevalence, which includes all current cases. Measures of association like relative risk and odds ratio quantify the relationship between exposure and outcome by comparing disease occurrence between exposed and unexposed groups. Measures of impact, such as attributable risk, indicate the extent to which a disease can be attributed to a given exposure.
2. Measurements of Morbidity and Mortality.pptxFerhanKadir
The most ambitious definition of health is that proposed by WHO in 1948: “health is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.” but,
Practical definitions of health and disease are needed in epidemiology, which concentrates on aspects of health that are easily measurable and amenable to improvement.
Definitions of health states used by epidemiologists tend to be simple, for example, “disease present” or “disease absent”
1. Incidence measures new cases of a disease over time in a population, while prevalence looks at all existing cases at a point or over a period of time.
2. Incidence can be expressed as a proportion or a rate incorporating time. Prevalence is always a proportion.
3. Examples are given calculating incidence proportion, incidence rate, and point and period prevalence from data. Morbidity measurements help describe disease burden and inform public health planning.
EPI_-_EPIDEMIOLOGIC_MEASURES in public health .pptxTofikMohammadMuse
This document discusses measures used to describe health events in populations, including ratios, proportions, and rates. It defines key terms like ratio, proportion, rate, incidence proportion, incidence density, point prevalence, and period prevalence. Examples are provided to demonstrate how to calculate various measures from population data, including the ratio of males to females, proportion of infants who lived, and incidence and prevalence rates. Mortality measures like crude mortality rate and category-specific rates are also defined.
Epidemiology is defined as the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems. It involves describing disease frequency, identifying causes, and providing data to plan prevention and control efforts. Key aspects include studying determinants like risk factors, the distribution of diseases among populations over time and place, and measuring outcomes like disease occurrence. Historical figures like John Snow used epidemiological methods to map disease spread and identify contaminated water as the source of a cholera outbreak.
Medical Surveillance and Outbreaks of Disease.pdfLuckyBoyCount
This document discusses key concepts in medical surveillance and epidemiology including:
- Medical surveillance involves the continuous collection of health data from a target population to identify disease patterns and outbreaks for prevention and control.
- Rates, proportions, and percentages are numerical metrics used to represent epidemiological findings. A rate is a ratio comparing two health measures over time.
- Morbidity refers to disease burden while mortality refers to deaths. Incidence measures new cases over time while prevalence measures all current cases.
- Correct classification of disease, symptoms, and exposures is important for epidemiological studies, as misclassification can bias results.
Epidemiology is defined as the study of distribution and determinants of health-related states or events in populations and the application of this study to control health problems. The key goals of epidemiology are to understand disease distribution, magnitude, determinants and risk factors in order to implement prevention and control measures to promote population health. Epidemiological studies use observational and experimental methods to collect data on disease occurrence with respect to time, place and person to measure disease burden and test hypotheses about disease etiology.
1. Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems. Descriptive epidemiology aims to describe patterns of disease, while analytical epidemiology aims to identify risk factors.
2. Key approaches in epidemiology include observational studies like cross-sectional and case-control studies, as well as experimental studies like randomized controlled trials. Important concepts include rates, ratios, and proportions used to describe disease frequency and distribution.
Health indicators are measures used to describe the health of a population and guide health policy. They include morbidity indicators like prevalence and incidence that measure disease burden, and mortality indicators like crude death rate. Common health indicators also track conditions like low birth weight and obesity. The document outlines how indicators like prevalence, incidence, and various death rates are calculated. It explains that prevalence represents existing cases at a time, while incidence measures new cases over time. Prevalence is influenced by incidence, mortality, and cure rates. Health indicators are important epidemiological tools.
Epidemiology is the study of disease frequency, distribution, and determinants in populations. Some key points about epidemiology include:
- It aims to describe disease problems, identify causes, and provide data to plan prevention and control efforts.
- Rates, ratios, and proportions are measurement tools used to compare disease occurrence between populations and time periods.
- Mortality data from death records can provide information about disease occurrence but have limitations like incomplete reporting.
- Morbidity data examines illness in populations and can be measured through incidence rates (new cases over time) and prevalence (all current cases).
- Descriptive studies examine disease frequency and distribution while analytical studies identify risk factors and experimental studies test hypotheses.
This document defines key terminology used in epidemiology and describes some important epidemiological methods. It defines epidemiology as the study of disease distribution and determinants in populations. Descriptive epidemiology organizes health data, while analytic epidemiology searches for causes and effects. Important measurements include rates, ratios and proportions to quantify disease frequency and distribution. Methods like incidence, prevalence, mortality and morbidity rates are used to measure disease occurrence and impact in populations.
Chapter 3Measures of Morbidity and Mortality Used in EpidemiolEstelaJeffery653
Chapter 3
Measures of Morbidity and Mortality Used in Epidemiology
Learning Objectives
Define and distinguish among ratios, proportions, and rates
Explain the term population at risk
Identify and calculate commonly used rates for morbidity, mortality, and natality
State the meanings and applications of incidence rates and prevalence
Learning Objectives (cont’d)
Discuss limitations of crude rates and alternative measures for crude rates
Apply direct and indirect methods to adjust rates
List situations where direct and indirect adjustment should be used
Overview of Epidemiologic Measures
Count
The simplest and most frequently performed quantitative measure in epidemiology.
Refers to the number of cases of a disease or other health phenomenon being studied.
Examples of Counts
Cases of influenza reported in Westchester County, New York, during January of a particular year.
Traffic fatalities in Manhattan in a 24-hour time period
College dorm students who had mono
Foreign-born stomach cancer patients
Ratio
The value obtained by dividing one quantity by another.
Consists of a numerator and a denominator.
The most general form has no specified relationship between numerator and denominator.
Rates, proportions, and percentages are also ratios.
Example of a
Simple Sex Ratio Calculation
A ratio may be expressed at = X/Y
Simple sex ratio (data from textbook)
Of 1,000 motorcycle fatalities, 950 victims are men and 50 are women.
Number of male cases 950
Number of female cases 50
19:1 male to female
=
=
Example of a
Demographic Sex Ratio Calculation
This ratio refers to the number of males per 100 females. In the U.S., the sex ratio in 2010 for the entire population was 96.7, indicating more females than males.
Number of male cases 151,781,326
Number of female cases 156,964,212
96.7
X 100 =
=
X 100
Example of a
Sex Ratio at Birth Calculation
The sex ratio at birth is defined as: (the number of male births divided by the number of female births) multiplied by 1,000.
Number of male births
Number of female births
X 1,000
Definition of Proportion
A measure that states a count relative to the size of the group.
A ratio in which the numerator is part of the denominator.
May be expressed as a percentage.
Uses of Proportions
Can demonstrate the magnitude of a problem.
Example: 10 dormitory students develop hepatitis. How important is this problem?
If only 20 students live in the dorm, 50% are ill.
If 500 students live in the dorm, 2% are ill.
Example of a Proportion
Calculate the proportion of African-American male deaths among African-American and white boys aged 5 to 14 years.
Rate
Definition: a ratio that consists of a numerator and a denominator and in which time forms part of the denominator.
Contains the following elements:
disease frequency
unit size of population
time period during which an event occurs
Crude death rate =
Number of deaths in a given y ...
The document discusses health indicators and how they are used to measure, compare, assess, monitor, and evaluate the health of communities. It provides characteristics that good health indicators should have such as being valid, reliable, sensitive, specific, feasible, and relevant. Examples of different types of health indicators are given, including mortality, morbidity, disability, nutritional status, health care delivery, and quality of life indicators. Formulas for calculating various epidemiological rates like crude death rate, specific death rates, proportional mortality rate, and case fatality rate are also presented.
This document defines and provides examples of different types of frequency measures used in epidemiology and public health, including ratios, proportions, rates, and other measures. It discusses how ratios, proportions, and rates are calculated, and provides specific formulas and examples. It also covers measures of morbidity like incidence and prevalence, and measures of mortality like crude mortality rates, cause-specific mortality rates, and others.
This document defines and provides examples of different types of frequency measures used in epidemiology and public health, including ratios, proportions, rates, and other measures. It discusses how ratios, proportions, and rates are calculated, and provides specific formulas and examples. It also covers measures of morbidity like incidence and prevalence, and measures of mortality like crude mortality rates, cause-specific mortality rates, and others.
This document discusses key concepts in epidemiology including rates, ratios, incidence, prevalence, mortality, and morbidity. It defines these terms and provides examples of how to calculate different rates. Specifically, it explains how to calculate crude death rate, infant mortality rate, maternal mortality rate, and prevalence. These basic health indicators are important for measuring changes over time, analyzing health situations, determining the magnitude of health problems, and allowing meaningful comparisons.
Measurement of Epidemiology
Radha Maharjan
MN (WHD)
Contents
5.1 Morbidity
Incidence
Prevalence
Attack Rate
Contents
5.2 Mortality
Crude Death Rate
Case Fatality Rate
Proportional Mortality Rate
Survival Rate
Standardized Death Rate
Contents
5.3 Disability
Disability Adjusted Life Years (DALY)
Quality Adjusted Life Years (QALY)
5.4 Tools of Measurements
Rate
Ratio
Proportion
5.4 Tools of Measurements
Numerator
Numerator refer to the number of times an event (e.g. number of birth) has occurred in a population, during a specified time period.
Denominator
Numerator has little meaning unless it is related to the denominator. The epidemiologist has to choose an appropriate denominator while calculating a rate.
It may be related to:
(I) population
(II) the total events.
Denominator related to the population
Mid year population
Population at risk
Person – time
Sub groups of the population
Denominator related to the Total Events
Mid year population
The population size changes daily due to births, deaths and migration, the mid year population is commonly chosen as a denominator.
The population as on 1st July is mid-year population.
Population at risk
It is important to note that the calculation of measures of disease frequency depends on correct estimates of the numbers of people under consideration.
Ideally, these figures should include only those people who are potentially susceptible to the disease studied.
Population at risk
For instance, men should not be included in denominator for the carcinoma of cervix.
Part of population, which is susceptible to a disease is called the population at risk,
e.g., Occupational injuries occur only among working people so the population at risk is the workforce.
Person – time
In some epidemiological studies (e.g. cohort studies), person may enter into the study at different times.
Consequently, they are under observation for varying time period.
In such case, the denominator is a combination of person and time.
Person – time
The most frequently used person time is person- years.
Some times this may be person- months, person -weeks or man- hours.
For example, if 10 persons were observed in the study for 10 years, person time would be 100 person years of observation.
Person – time
The same figure would be derived if 100 persons were under observation for one year.
These denominators have the advantage of summarizing the experience of persons with different duration of observation or exposure.
Sub groups of the population
The denominator may be subgroups of population
e.g. under-five, female, doctors, etc.
Denominator related to the Total Events
In some instances, the denominator may be related to total events instead of the total population, as in the case of infant mortality rate the denominator is total number of live births.
Definition concept and comparison of ratio, proportion and rate.
MEASURES OF DISEASE FREQUENCY. ASSOSCIATION AND IMPACTAneesa K Ayoob
This document discusses various measures used to quantify disease frequency, association, and impact in epidemiology. It defines key terms like incidence, prevalence, risk, rate, and ratio. For measures of disease frequency, it distinguishes between incidence, which considers new cases over time, and prevalence, which includes all current cases. Measures of association like relative risk and odds ratio quantify the relationship between exposure and outcome by comparing disease occurrence between exposed and unexposed groups. Measures of impact, such as attributable risk, indicate the extent to which a disease can be attributed to a given exposure.
2. Measurements of Morbidity and Mortality.pptxFerhanKadir
The most ambitious definition of health is that proposed by WHO in 1948: “health is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.” but,
Practical definitions of health and disease are needed in epidemiology, which concentrates on aspects of health that are easily measurable and amenable to improvement.
Definitions of health states used by epidemiologists tend to be simple, for example, “disease present” or “disease absent”
1. Incidence measures new cases of a disease over time in a population, while prevalence looks at all existing cases at a point or over a period of time.
2. Incidence can be expressed as a proportion or a rate incorporating time. Prevalence is always a proportion.
3. Examples are given calculating incidence proportion, incidence rate, and point and period prevalence from data. Morbidity measurements help describe disease burden and inform public health planning.
EPI_-_EPIDEMIOLOGIC_MEASURES in public health .pptxTofikMohammadMuse
This document discusses measures used to describe health events in populations, including ratios, proportions, and rates. It defines key terms like ratio, proportion, rate, incidence proportion, incidence density, point prevalence, and period prevalence. Examples are provided to demonstrate how to calculate various measures from population data, including the ratio of males to females, proportion of infants who lived, and incidence and prevalence rates. Mortality measures like crude mortality rate and category-specific rates are also defined.
Epidemiology is defined as the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems. It involves describing disease frequency, identifying causes, and providing data to plan prevention and control efforts. Key aspects include studying determinants like risk factors, the distribution of diseases among populations over time and place, and measuring outcomes like disease occurrence. Historical figures like John Snow used epidemiological methods to map disease spread and identify contaminated water as the source of a cholera outbreak.
Medical Surveillance and Outbreaks of Disease.pdfLuckyBoyCount
This document discusses key concepts in medical surveillance and epidemiology including:
- Medical surveillance involves the continuous collection of health data from a target population to identify disease patterns and outbreaks for prevention and control.
- Rates, proportions, and percentages are numerical metrics used to represent epidemiological findings. A rate is a ratio comparing two health measures over time.
- Morbidity refers to disease burden while mortality refers to deaths. Incidence measures new cases over time while prevalence measures all current cases.
- Correct classification of disease, symptoms, and exposures is important for epidemiological studies, as misclassification can bias results.
Epidemiology is defined as the study of distribution and determinants of health-related states or events in populations and the application of this study to control health problems. The key goals of epidemiology are to understand disease distribution, magnitude, determinants and risk factors in order to implement prevention and control measures to promote population health. Epidemiological studies use observational and experimental methods to collect data on disease occurrence with respect to time, place and person to measure disease burden and test hypotheses about disease etiology.
1. Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems. Descriptive epidemiology aims to describe patterns of disease, while analytical epidemiology aims to identify risk factors.
2. Key approaches in epidemiology include observational studies like cross-sectional and case-control studies, as well as experimental studies like randomized controlled trials. Important concepts include rates, ratios, and proportions used to describe disease frequency and distribution.
Health indicators are measures used to describe the health of a population and guide health policy. They include morbidity indicators like prevalence and incidence that measure disease burden, and mortality indicators like crude death rate. Common health indicators also track conditions like low birth weight and obesity. The document outlines how indicators like prevalence, incidence, and various death rates are calculated. It explains that prevalence represents existing cases at a time, while incidence measures new cases over time. Prevalence is influenced by incidence, mortality, and cure rates. Health indicators are important epidemiological tools.
Epidemiology is the study of disease frequency, distribution, and determinants in populations. Some key points about epidemiology include:
- It aims to describe disease problems, identify causes, and provide data to plan prevention and control efforts.
- Rates, ratios, and proportions are measurement tools used to compare disease occurrence between populations and time periods.
- Mortality data from death records can provide information about disease occurrence but have limitations like incomplete reporting.
- Morbidity data examines illness in populations and can be measured through incidence rates (new cases over time) and prevalence (all current cases).
- Descriptive studies examine disease frequency and distribution while analytical studies identify risk factors and experimental studies test hypotheses.
This document defines key terminology used in epidemiology and describes some important epidemiological methods. It defines epidemiology as the study of disease distribution and determinants in populations. Descriptive epidemiology organizes health data, while analytic epidemiology searches for causes and effects. Important measurements include rates, ratios and proportions to quantify disease frequency and distribution. Methods like incidence, prevalence, mortality and morbidity rates are used to measure disease occurrence and impact in populations.
Chapter 3Measures of Morbidity and Mortality Used in EpidemiolEstelaJeffery653
Chapter 3
Measures of Morbidity and Mortality Used in Epidemiology
Learning Objectives
Define and distinguish among ratios, proportions, and rates
Explain the term population at risk
Identify and calculate commonly used rates for morbidity, mortality, and natality
State the meanings and applications of incidence rates and prevalence
Learning Objectives (cont’d)
Discuss limitations of crude rates and alternative measures for crude rates
Apply direct and indirect methods to adjust rates
List situations where direct and indirect adjustment should be used
Overview of Epidemiologic Measures
Count
The simplest and most frequently performed quantitative measure in epidemiology.
Refers to the number of cases of a disease or other health phenomenon being studied.
Examples of Counts
Cases of influenza reported in Westchester County, New York, during January of a particular year.
Traffic fatalities in Manhattan in a 24-hour time period
College dorm students who had mono
Foreign-born stomach cancer patients
Ratio
The value obtained by dividing one quantity by another.
Consists of a numerator and a denominator.
The most general form has no specified relationship between numerator and denominator.
Rates, proportions, and percentages are also ratios.
Example of a
Simple Sex Ratio Calculation
A ratio may be expressed at = X/Y
Simple sex ratio (data from textbook)
Of 1,000 motorcycle fatalities, 950 victims are men and 50 are women.
Number of male cases 950
Number of female cases 50
19:1 male to female
=
=
Example of a
Demographic Sex Ratio Calculation
This ratio refers to the number of males per 100 females. In the U.S., the sex ratio in 2010 for the entire population was 96.7, indicating more females than males.
Number of male cases 151,781,326
Number of female cases 156,964,212
96.7
X 100 =
=
X 100
Example of a
Sex Ratio at Birth Calculation
The sex ratio at birth is defined as: (the number of male births divided by the number of female births) multiplied by 1,000.
Number of male births
Number of female births
X 1,000
Definition of Proportion
A measure that states a count relative to the size of the group.
A ratio in which the numerator is part of the denominator.
May be expressed as a percentage.
Uses of Proportions
Can demonstrate the magnitude of a problem.
Example: 10 dormitory students develop hepatitis. How important is this problem?
If only 20 students live in the dorm, 50% are ill.
If 500 students live in the dorm, 2% are ill.
Example of a Proportion
Calculate the proportion of African-American male deaths among African-American and white boys aged 5 to 14 years.
Rate
Definition: a ratio that consists of a numerator and a denominator and in which time forms part of the denominator.
Contains the following elements:
disease frequency
unit size of population
time period during which an event occurs
Crude death rate =
Number of deaths in a given y ...
The document discusses health indicators and how they are used to measure, compare, assess, monitor, and evaluate the health of communities. It provides characteristics that good health indicators should have such as being valid, reliable, sensitive, specific, feasible, and relevant. Examples of different types of health indicators are given, including mortality, morbidity, disability, nutritional status, health care delivery, and quality of life indicators. Formulas for calculating various epidemiological rates like crude death rate, specific death rates, proportional mortality rate, and case fatality rate are also presented.
This document defines and provides examples of different types of frequency measures used in epidemiology and public health, including ratios, proportions, rates, and other measures. It discusses how ratios, proportions, and rates are calculated, and provides specific formulas and examples. It also covers measures of morbidity like incidence and prevalence, and measures of mortality like crude mortality rates, cause-specific mortality rates, and others.
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3. COUNT
• The simplest and most frequently performed quantitative measure in
epidemiology is a count.
• A count refers merely to the number of cases of a disease or other health
phenomenon being studied.
• Several examples of counts are the number of:
• Cases of covid-19 reported in Punjab, Pakistan, during September of a 2021
• Traffic fatalities in the Lahore during a 24-hour period
4. RATIO
• A ratio is defined as “The value obtained by dividing one quantity by another.”
• RATE, PROPORTION, and PERCENTAGE are types of ratios.
• A ratio therefore consists of a numerator and a denominator.
• A ratio may be expressed as follows: ratio = X/Y.
7. PROPORTION
• A proportion is a type of ratio in which the numerator is part of the denominator; proportions may be
expressed as percentages.
• Let us consider how a proportion can be helpful in describing health issues by reexamining a count.
• For a count to be descriptive of a group, it usually should be seen relative to the size of the group.
• Suppose there were 10 college dorm residents who had hepatitis. How large a problem did these 10
cases represent? To answer this question, one would need to know whether the dormitory housed
20 students or 500 students. If there were only 20 students, then 50% (or 0.50) were ill. Conversely,
if there were 500 students in the dormitory, then only 2% (or 0.02) were ill. Clearly, these two
scenarios paint a completely different picture of the magnitude of the problem.
8. EXAMPLE
Number of deaths among African-
American boys (A)
Number of deaths among white
boys (B)
Total
(A+B)
1150 3810 4960
Calculation of the Proportion of African-American Male Deaths Among African-
American and White Boys Aged 5 to 14 Years
Proportion = A/(A + B) × 100 = (1,150/4,960) × 100 =
23.2%
9. RATE
• A rate also is a type of ratio; however, a rate differs from a proportion because the
denominator involves a measure of time.
• The numerator consists of the frequency of a disease over a specified period of
time, and the denominator is a unit size of population.
• It is critical to remember that to calculate a rate, two periods of time are involved:
the beginning of the period and the end of the period.
11. RATES
• Rates improve one’s ability to make comparisons, although they also have limitations.
• Rates of mortality or morbidity for a specific disease reduce that standard of comparison to a
common denominator, the unit size of population.
• To illustrate, the U.S. crude death rate for diseases of the heart in 2003 was 235.6 per 100,000.
One also might calculate the heart disease death rate for geographic subdivisions of the country.
These rates could then be compared with one another and with the rate for the United States to
judge whether the rates found in each geographic area are higher or lower. For example, the
crude death rates for diseases of the heart in New York and Texas were 288.0 and 188.9 per
100,000, respectively. It would appear that the death rate is higher in New York than in Texas
based on the crude death rates. This may be a specious conclusion, however, because there
may be important differences in population composition that would affect mortality experience.
12. RATES
• Rates can be expressed in any form that is convenient (e.g., per 1,000, per 100,000, or per
1,000,000).
• Many of the rates that are published and routinely used as indicators of public health are
expressed in particular conventions.
• For example, cancer rates are typically expressed per 100,000 population, and infant mortality is
expressed per 1,000 live births.
• One of the determinants of the size of the denominator is whether the numerator is large enough
to permit the rate to be expressed as an integer or an integer plus a trailing decimal (e.g., 4 or
4.2). For example, it would be preferable to describe the occurrence of disease as 4 per 100,000
(or 4.2 per 100,000) rather than 0.04 per 1,000 (or 0.042 per 1,000), even though both are
perfectly correct.
13. PREVALENCE
• The term prevalence refers to the number of existing cases of a disease or health
condition in a population at some designated time.
• Prevalence data provide an indication of the extent of a health problem and thus
may have implications for the scope of health services needed in the community.
• Prevalence can be expressed as a number, a percentage, or number of cases per
unit size of population
14. POINT PREVALENCE
• When the time period is unspecified, prevalence usually implies a
particular point in time.
• Example
• The prevalence of diarrhea in a children’s camp on July 13 was 15,
• The prevalence of phenylketonuria-associated mental disabilities in institutions for the
developmentally disabled was 15%, and
• The prevalence of obesity among women aged 55–69 years was 367 per 1,000.
• These examples illustrate that the designated time can be specified (e.g., one day) or
unspecified.
16. PERIOD PREVALENCE
• A second type of prevalence measure is period prevalence, which denotes the total number of
cases of a disease that exist during a specified period of time, for instance a week, month, or
longer time interval.
• To determine the period prevalence, one must combine the number of cases at the beginning of
• the time interval) with the new cases that occur during the interval.
• Note that for period prevalence, cases are counted even if they die, migrate, or recur as
episodes during the period.
18. INCIDENCE
• Prevalence measures the frequency of existing cases of disease in a population. In
contrast, incidence is a measure of the number of new cases of a disease (or
another health outcome) that develop in a population of individuals at risk, during
a specified time period.
• There are two main measures of incidence:
19.
20. RISK
• This is also known as cumulative incidence because it refers to the occurrence of risk events,
such as disease or death, in a group studied over time.
• It is the proportion of individuals in a population initially free of disease who develop the
disease within a specified time interval.
• Incidence risk is expressed as a percentage (or, if small, as “per 1000 persons”).
•
21. RISK
• Remember that the denominator is the total number of people who were free of disease at the
start of the study period (the population at risk). The cumulative incidence assumes that the
entire population at risk at the beginning of the study period has been followed for the
specified time period for the development of the outcome under investigation. This is called
a closed population.
• However, in reality in a cohort study, for example, participants are followed up for a long period
of time and the population will change as people enter and leave. This is called
a dynamic population. Some may develop the outcome of interest, or be lost during follow-
up, for a variety of other reasons:
Refusal to continue to participate in the study
Migration
Death
22. INCIDENCE RATE
• Incidence rates also measure the frequency of new cases of disease in a population, but take
into account the sum of the time that each participant remained under observation and at risk
of developing the outcome under investigation.
• This measurement also seeks to account for varying time periods of follow up, which may
occur for the reasons outlined above.
23. INCIDENCE RATE
• An example of incidence measured as a frequency is the number of new cases of HIV infection
diagnosed in a population in a given year: A total of 164 HIV diagnoses were reported among
American Indians or Alaska natives in the United States during 2009.
25. TIME AT RISK
• In a dynamic population, individuals in the group may have been at risk for different lengths of
time, so instead of counting the total number of individuals in the population at the start of the
study, the time each individual spends in the study before developing the outcome of interest
needs to be calculated.
• The denominator in an incidence rate is the sum of each individual's time at risk (i.e. the length
of time they were followed up in the study). It is commonly expressed as person years at risk.
• The incidence rate is the rate of contracting the disease among those still at risk. When a study
subject develops the disease, dies or leaves the study, they are no longer at risk and will no
longer contribute person-time units at risk.
26. TIME AT RISK
• Figure illustrates the
calculation of person-
time units (years) at
risk of a hypothetical
population of 5
individuals in a 5 year
cohort study.
27. ODDS
Another method of measuring incidence is to calculate the odds of disease. Instead of
using the number of individuals who are disease-free at the start of the study, odds
are calculated using the number disease-free at the end of the time period.
28. THE RELATIONSHIP BETWEEN PREVALENCE AND INCIDENCE
• The proportion of the population that has a disease at a point in time (prevalence)
and the rate of occurrence of new disease during a period of time (incidence) are
closely related.
• Prevalence depends on:
1. The incidence rate
2. The duration of disease
29. THE RELATIONSHIP BETWEEN PREVALENCE AND INCIDENCE
• For example, if the incidence of a disease is low but the duration of disease (i.e. time until
recovery or death) is long, the prevalence will be high relative to the incidence. An example of
this would be diabetes.
• Conversely, if the incidence of a disease is high and the duration of the disease is short, the
prevalence will be low relative to the incidence. An example of this would be influenza.
• A change in the duration of a disease, for example the development of a new treatment that
prevents death but does not result in a cure, will lead to an increase in prevalence without
affecting incidence. Fatal diseases, or diseases from which a rapid recovery is common, have a
low prevalence, whereas diseases with a low incidence may have a high prevalence if they are
incurable but rarely fatal and have a long duration.
• The relationship between incidence and prevalence can be expressed as;
• P = ID
• (P = Prevalence, I = Incidence Rate, D = Average duration of the disease)
31. ATTACK RATE
• The attack rate (AR) is an alternative form
of the incidence rate that is used when the
nature of the disease or condition is such
that a population is observed for a short
time period, often as a result of specific
exposure.
• In reporting outbreaks of salmonella
infection or other foodborne types of
gastroenteritis, epidemiologists employ the
AR
As shown in this formula, the numerator
consists of people made ill as a result of
exposure to the suspected agent, and the
denominator consists of all people, whether
well or ill, who were exposed to the agent
during a time
period.
32. MEASURES OF EFFECT
• Measures of effect are used in epidemiological studies to assess the strength of an association
between a putative risk factor and the subsequent occurrence of disease.
• This is done by comparing the incidence of disease in a group of persons exposed to a
potential risk factor with the incidence in a group who have not been exposed.
• This comparison can be summarized by calculating either:
The ratio of measures of disease frequency for the two groups
The difference between the two
33. A. RELATIVE MEASURES
• Relative measures reflect the increase in frequency of disease in one population (e.g. exposed)
versus another (e.g. not exposed), which is treated as the baseline. They are often collectively
referred to as measures of relative risk.
• The relative risk is a measure of the strength of an association between an exposure and
disease, and can be used to assess whether an observed association is likely to be causal.
• The most commonly used measure of effect is the ratio of incidence rates
• Rate (or risk) in exposed
Rate (or risk) in unexposed
• There are three main measures of effect:
34.
35. INTERPRETING RELATIVE RISK (RR)
• Measures of effect such as the risk ratio provide assessments of aetiological strength, or the
strength of association between a putative risk factor and an outcome.
• A relative risk of 1 indicates that the incidence of disease in the exposed and unexposed
groups is identical and that there is no association observed between the disease and risk
factor/ exposure.
• A relative risk > 1 occurs when the risk of disease is greater among those exposed and
indicates a positive association, or an increased risk among those exposed to the risk factor
compared with those unexposed.
• A relative risk < 1 occurs when the risk of disease is lower in those exposed compared to
those unexposed and indicates a negative association.
36. ABSOLUTE MEASURES
• Relative measures help evaluate how strongly an exposure is associated with a particular disease,
but they do not give an indication of the impact of the exposure in the population. This is
important for public health prevention measures.
• Absolute measures indicate exactly what impact a disease will have on a population, in terms of
numbers or proportions affected by being exposed.
• For example, a study finds that having several CT head scans in childhood results in a three-fold
increase of your risk of developing brain cancer as an adult. This sounds like a large increase, but
because the absolute risk increase would be small (say, an increase of 0.5 cases per 10,000
children), the increased risk means one additional case of brain cancer per 20,000 children
scanned.
37. ATTRIBUTABLE RISK (RISK DIFFERENCE)
• The attributable risk (AR) is a measure of association that provides information about the
absolute effect of the exposure or excess risk of disease in those exposed compared with the
unexposed, assuming the risk is causal.
• It tells us exactly how many more people are affected in the exposed group, than in the
unexposed.
• The risk or rate difference estimates the excess risk caused by exposure in the exposed
group.
38. ATTRIBUTABLE RISK PERCENTAGE
• AR may also be expressed as the proportion of disease cases in the exposed group
attributable to the exposure (i.e. the proportion of additional cases in the exposed
group).
• This is also known as the aetiologic fraction or attributable fraction. It is calculated
as follows: