Transcript Slide 1

Module 1 Overview
Context
Content Area: Descriptive Epidemiology & Surveillance
Essential Question (Generic): How are health-related states or events distributed?
Essential Question (Drug Abuse Specific): How is drug abuse distributed?
Enduring Epidemiological Understanding: The frequency and distribution of healthrelated states or events in a population can be determined by systematically
collecting, analyzing, and interpreting data.
Synopsis
In Module 1, students explore how to describe the distribution of health-related states
or events. Students begin to uncover and develop the following epidemiological
concepts and skills: observing groups of people, counting, the value of a denominator,
a case definition, a representative sample, and creating circumstances that encourage
truthful responses and protect confidentiality.
Lesson 1-1:
Lesson 1-2:
Lesson 1-3:
Lesson 1-4:
Lesson 1-5:
Lesson 1-6:
DrugEpi 1-1 Counting & Rates
Counting and Rates
Introduction to Surveillance
Counting/Describing HIV / AIDS
Counting High School Marijuana Use
National Survey on Drug Use and Health
Other Drug Abuse Surveillance Systems
Module 1 - Descriptive Epidemiology and Surveillance
Lesson 1-1 Counting and Rates
Content
• Definitions of epidemiology, descriptive epidemiology, population science
• Expressing what is observed in numbers / counts
• Adding denominators to increase information from counts: creating ratios,
proportions, rates
• Getting comfortable with rates
• Rates used in epidemiology
Big Ideas
• Epidemiology uses population science to describe patterns of disease
and health
• Counts become more meaningful with a denominator
• Denominators allow us to calculate proportions, percentages and rates,
and compare different groups
• People go in and out of the numerator (incidence versus prevalence)
This project is supported by a Science Education Drug Abuse Partnership Award, Grant Number 1R24DA016357-01,
from the National Institute on Drug Abuse, National Institutes of Health.
DrugEpi 1-1 Counting & Rates
Where are we?
Essential Questions
Enduring Understandings
1.
How is this disease
distributed?
Health-related conditions and behaviors are not distributed uniformly
in a population. They have unique distributions that can be described
by how they are distributed in terms of person, place, and time.
2.
What hypotheses might
explain the distribution of
disease?
Clues for formulating hypotheses can be found by observing the way
a health-related condition or behavior is distributed in a population.
3.
Is there an association
between the
hypothesized cause and
the disease?
Causal hypotheses can be tested by observing exposures and
diseases of people as they go about their daily lives. Information
from these observational studies can be used to make and compare
rates and identify associations.
4.
Is the association
causal?
Causation is only one explanation for an association between an
exposure and a disease. Because observational studies are
complicated by factors not controlled by the observer, other
explanations also must be considered.
5.
What should be done
when preventable
causes of disease are
found?
Policy decisions are based on more than the scientific evidence.
Because of competing values - social, economic, ethical,
environmental, cultural, and political factors may also be considered.
DrugEpi 1-1 Counting & Rates
Review: Definition of Epidemiology
“… the study of the distribution and determinants
of health-related states or events in specific
populations and the application of this study to the
control of health problems.” Gordis 2004
DrugEpi 1-1 Counting & Rates
Epidemiology - Study at the Population Level
“… the study of the distribution and determinants
of health-related states or events in specific
populations and the application of this study to the
control of health problems.”
DrugEpi 1-1 Counting & Rates
Descriptive Epidemiology
“… the study of the distribution and determinants
of health-related states or events in specific
populations and the application of this study to the
control of health problems.”
DrugEpi 1-1 Counting & Rates
Descriptive Epidemiology
Epidemiologic studies that are concerned with
characterizing the amount and distribution of health
and disease within a population.
DrugEpi 1-1 Counting & Rates
Descriptive Epidemiology
Distribution 1
Describe what you observe
Express it in numbers
DrugEpi 1-1 Counting & Rates
Descriptive Epidemiology
Lord Kelvin
1824-1907
When you can measure what you are speaking about,
and express it in numbers, you know something about it.
But when you cannot measure it, when you cannot express it in numbers,
your knowledge is of a meager and unsatisfactory kind.
DrugEpi 1-1 Counting & Rates
Epidemiologists Like to Count Things Related to Health
What do Epidemiologists count?
Numbers of people who get sick
Numbers of people who die
Numbers of people with a certain health habit
Numbers of people with a certain exposure
But, epidemiologists do more than count
DrugEpi 1-1 Counting & Rates
Real Example
Figure 7.2
Dependence on or Abuse of Specific Illicit Drugs
in the Past Year among Persons Aged 12 or Older: 2005
DrugEpi 1-1 Counting & Rates
Epidemiologists Do More Than Count
But, epidemiologists do more than count
DrugEpi 1-1 Counting & Rates
Epidemiologists Do More Than Count
Town A has 27 new cases of
cocaine dependence/abuse in April
Town B has 94 new cases of
cocaine dependence/abuse in April
What do these counts mean
about the impact of cocaine dependence/abuse?
It depends . . . need a context
It depends on the number of people in Towns A and B
In other words, it depends on denominators
- a basis for comparison
DrugEpi 1-1 Counting & Rates
Epidemiology Toolbox
Denominators give us context
For example:
• Town A has 27 new cases of cocaine
dependence/abuse in a population of 1000
•
Town B has 94 new cases of cocaine
dependence/abuse in a population of 5000
With a denominator we can now calculate
• Proportions
• Percentages
• Rates
DrugEpi 1-1 Counting & Rates
Epidemiology Toolbox: Proportions
Numerator
#
#
Denominator
= Proportion
… when the people in the numerator are included in the
denominator
DrugEpi 1-1 Counting & Rates
Epidemiology Toolbox: Proportions
Town A
Numerator
Proportion
27
27/1000 = 0.027
1000
Denominator
… the proportion of new cases of
cocaine dependence/abuse in April in Town A is 0.027
DrugEpi 1-1 Counting & Rates
Epidemiology Toolbox: Percentages
Numerator
#
#
Denominator
X 100 =
Percentage
… when the people in the numerator are included in the
denominator and the decimal is multiplied by 100
DrugEpi 1-1 Counting & Rates
Epidemiology Toolbox: Percentages
Town B
Numerator
94
0.019 X 100 =
1.9%
5000
Denominator
… 1.9% of the people in Town B were identified as
dependent upon or abusing cocaine in April
DrugEpi 1-1 Counting & Rates
Epidemiology Toolbox: Rates
Numerator everyone with the
outcome of interest
= Rate
in a given time
period
Denominator - everyone
at risk for the health
outcome of interest, i.e.,
the population at risk, in
a certain time period
… when the people in the numerator are included in the
denominator, and there is a a time frame
DrugEpi 1-1 Counting & Rates
Epidemiology Toolbox: Rates
Numerator
Rate
0.027 x 1000
27
= 27 cases per 1000
1000
per month
Denominator
… the rate of new cases of cocaine dependence/abuse
in Town A is 27 cases per 1000 per month
DrugEpi 1-1 Counting & Rates
Epidemiology Toolbox: Rates
Numerator
Rate
0.019 x 1000
94
= 19 cases per 1000
5000
per month
Denominator
… the rate of new cases of cocaine dependence/abuse
in Town B is 19 cases per 1000 per month
DrugEpi 1-1 Counting & Rates
Epidemiology Toolbox: Big Ideas about Rates
Because rates can use common denominators,
it is easier to compare rates
between towns (or other groups)
with different population sizes
Because rates can specify a time frame,
they tell us about the “speed” of a disease
DrugEpi 1-1 Counting & Rates
Summary of Proportions, Percentage, Rates
Proportion
Percentage
Rate
DrugEpi 1-1 Counting & Rates
A proportion is a ratio in which the
numerator is a subset of the
denominator.
A percentage is a proportion X 100.
An example is the percentage of
AIDS patients who die.
Also a type of proportion, a rate
should include a time factor. An
example is new cases of a disease in
a certain population per year.
Descriptive Epidemiology
Distribution 2
DrugEpi 1-1 Counting & Rates
Descriptive Epidemiology
Describe what you observe
Express what you observe in numbers
DrugEpi 1-1 Counting & Rates
Descriptive Epidemiology
Distribution 3
Describe what you observe
Express what you observe in numbers.
DrugEpi 1-1 Counting & Rates
Descriptive Epidemiology
Count
DrugEpi 1-1 Counting & Rates
Divide
Compare
Descriptive Epidemiology
Count
DrugEpi 1-1 Counting & Rates
Divide
Compare
Getting Comfortable with Rates
Review
In epidemiology, a rate expresses the impact of a
disease or other health-related condition in a
defined population in a specified time frame
# of health-related
events in the
Rate = population at risk
# of people in the
population at risk
DrugEpi 1-1 Counting & Rates
xK
per a defined
time period
A multiplier or constant such as
per 1000 or 100,000 people
Types of Rates in Epidemiology and Public Health
One distinction is mortality versus morbidity rates
● Mortality - part of “Vital” Statistics
 Mortality (national, state and local rates
 Natality (such as infant death rates)
● Morbidity - unhealthy, state of disease/sickness
 Health Surveys
 Cancer registries
 Infectious disease statistics
 Drug abuse surveys
Denominators to define population at risk?
Remember the Census!
DrugEpi 1-1 Counting & Rates
Types of Rates in Epidemiology and Public Health
Another distinction is incidence rates
versus prevalence rates
● Incidence rate =
Number of new cases of a disease
Total population at risk
For a given
time period
For a given
point in time
Number of existing cases of a disease or time
period
● Prevalence rate =
Total population
DrugEpi 1-1 Counting & Rates
Prevalence Pot
Incidence
In
Out
Prevalence
Prevalence
Pot
Pot
DrugEpi 1-1 Counting & Rates
Recovery
Death
Prevalence Pot
Incidence
In
Out
Prevalence
Pot
DrugEpi 1-1 Counting & Rates
Recovery
Death
Prevalence Pot
In
Out
27
157
27 + 157 - 14 - 5 = 165
DrugEpi 1-1 Counting & Rates
14
5
Re-Cap
Big Ideas in this Lesson (1-1)
• Epidemiology uses population science to describe
patterns of disease and health
• Counts become more meaningful with a denominator
• Denominators allow us to calculate proportions,
percentages and rates, and compare different groups
• People go in and out of the numerator (incidence
versus prevalence)
This project is supported by a Science Education Drug Abuse Partnership Award, Grant Number 1R24DA016357-01,
from the National Institute on Drug Abuse, National Institutes of Health.
DrugEpi 1-2 Introduction to Surveillance
Next Lesson (1-2)
Population Surveillance
DrugEpi 1-2 Introduction to Surveillance