2. What did we learn in Lecture 1?
A quick Recap
ā¢ Definition of epidemiology
ā āThe study of the distribution and determinants of health-related states or
events in specified populations, and the application of this study to the
prevention and control of health problemsā
ā¢ The Epidemiological Approach
ā Asking Questions
ā Making comparisons
ā¢ The aims of epidemiology
ā Describe disease ā Distribution, frequency
ā Identify etiological factors
ā Provide data for planning and implementation and for priority setting
3. Lecture Objectives
By the end of this lecture, the student will be
able to:
1. Describe the tools of measurements in
epidemiology.
2. Enumerate the FIVE elements in a rate.
3. Define and differentiate between incidence and
prevalence.
4. Enumerate types of prevalence.
5. Calculate the prevalence of a disease/health-
related behavior in a population.
4. Definitions and terms
ā¢ Operational Definition:
ā āA definition embodying criteria used to identify
and classify individual members of a set or
concept to facilitate classification and counting.ā
ā¢ Population at risk:
ā āPeople who are potentially susceptible to the
disease under studyā.
ā āThe group of people, healthy or sick, who would
be counted as cases if they had the disease being
studiedā.
7. RATIO
ā¢ āThe value obtained by dividing one quantity
by anotherā
ā¢ Example: Sex ratio, Child-woman ratio
8. RATE
ā¢ āthe frequency with which an event occurs in
a defined population, usually in a specified
period of timeā.
ā¢ Example: Incidence rate
9. PROPORTION
ā¢ āThe ratio of a part to the whole, expressed as
a ādecimal fractionā (e.g., 0.2), as a ācommon
fractionā (1/5), or as a percentage (20%)ā. The
proportion is a dimensionless quantity.
ā¢ Example: Proportion of diabetics in a
population.
10. The FIVE elements (or components)
of a rate
Rate =
Number of events in a specified
population during a specified period
Average population during
the period
X 10
n
Numerator
Denominator
Multiplier
Time
Population
12. INCIDENCE ā WHAT IS IT?
ā¢ āthe number of new health-related events in a
defined population within a specified period
of time. It may be measured as a frequency
count, a rate, or a proportionā.
13. PREVALENCE ā WHAT IS IT?
ā¢ ātotal number of individuals who have an attribute or
disease at a particular time (it may be a particular
period) divided by the population at risk of having
the attribute or disease at that time or midway
through the periodā.
ā¢ A measure of occurrence or disease frequency, often
used to refer to the proportion of individuals in a
population who have a disease or condition.
ā¢ When used without qualification, the term usually
refers to the situation at a specified point in time
(point prevalence).
ā¢ It is a proportion, not a rate.
16. Definition of prevalence
ā¢ ātotal number of individuals who have an
attribute or disease at a particular time (it may be
a particular period) divided by the population at
risk of having the attribute or disease at that time
or midway through the periodā.
ā¢ A measure of occurrence or disease frequency,
often used to refer to the proportion of
individuals in a population who have a disease or
condition.
ā¢ It refers to NEW+OLD cases of the disease.
18. ā¢ Point prevalence
ā The proportion of individuals with a disease or an
attribute at a specified point in time.
Types of prevalence
19. ā¢ Period prevalence
ā¢ The proportion of individuals with a disease or an
attribute at a specified period of time.
ā¢ To calculate a period prevalence, the denominator
used most commonly is the āpopulation at risk
midway through the periodā (e.g., mid-year
population)
Types of prevalence ā contd ā¦
20. ā¢ Lifetime prevalence
ā The proportion of individuals who have had the
disease or condition for at least part of their lives
at any time during their lifecourse.
Types of prevalence ā contd ā¦
22. ā¢ Estimate the magnitude of health/disease
problems in the community and identify
potential high-risk population groups.
ā¢ Assessing the need for preventive action,
healthcare and the planning of health
services.
ā¢ Prevalence is a useful measure of the occurrence
of conditions for which the onset of disease may
be gradual, such as hypertension, diabetes or
rheumatoid arthritis.
Uses of prevalence
23. ā¢ Prevalence studies do not usually provide
strong evidence of causality.
Disadvantages of prevalence
24. EXERCISES
ā¢ Calculate the prevalence of disease in the
given situations.
ā¢ SITUATION 1:
ā¢ In a population of 30000, 200 adolescents girls
are anemic. Calculate the prevalence of
anemia among adolescent girls if adolescent
girls comprise 10% of the population?
25. ā¢ SITUATION 2:
Jan 1,
2013
Dec 31,
2013
Population at risk =200
(on 1st July, 2013)