2. Objectives
• To know the meaning of epidemiology
• To know the types & basic tools of
epidemiology
• To get acquainted with the uses of
epidemiology
4. Introduction
• Epidemiology is central in community
medicine, as it addresses the health problems
in a defined population.
• This becomes very crucial where we have
outbreak of disease
5. Definition
• The study of the distribution and determinants
of health-related states or events in specified
human populations and the application of this to
the control of health problems. John M. Last
1988
• Distribution: Frequency (rates & risks) & pattern
of health events(time, place & person).
• Determinants: Factors or events that are capable
of bringing about a change in health.
6. Definition Cont’
• Human population: Epidemiology examines
health events among population groups rather
than individuals.
• Health-related states: infections, chronic diseases
& physiological events & various states of health
such as disability, injury, mortality.
• Health-related events: it can be use to evaluate
Immunization coverage, hospital attendance, bed
occupancy.
• Application: this serves as basis for directing
intervention.
7. Classification
The methods can be classified into:
• Observational
o Descriptive – Case report, Case series, Correlational
(Ecologic), Cross sectional
o Analytical – Case control, Cohort
• Experimental/Interventional
o Randomized controlled trials
o Field trials
o Community trials
8. Descriptive
• The distribution of disease is describe in terms
of
- Person
- Place and
- Time
• Answers to these help in developing an
hypothesis
11. 11
Time
• Short Term Trends
• Seasonal Or Cyclic Trends
• Long Term Or Secular Trends
12. Analytical Epidemiology
• There are two types:
- Case control study (Also known as
retrospective study or case-history study) and
- Cohort study
13. Case Control Study
• A study that compares patients who have a
disease or outcome of interest [cases] with
patients who do not have the disease or
outcome of interest [controls] and looks back
retrospectively to compare how frequently an
exposure to a given factor is present in each
group to determine the relationship between
risk factor and disease.
14. Cohort study
• A cohort was a 300- 600 man unit in the
Roman army. A cohort study consists of a
group of people marching through time from
an exposure to one or more outcomes. The
studies follow up two or more groups from
exposure to outcome. The goal is usually to
measure incidence.
15. Classification
• Prospective (concurrent): Cohort is
assembled, baseline observations and data
collected for purpose of study
• Retrospective (historical): Cohort is assembled
in the past on the basis of records. Some data
might be missing
• Bidirectional (mixed): Includes both elements
16. Differences btw case control and
cohort
CASE CONTROL
• Proceed from effect to cause
• Start with the dx
• Give quick result
• Involve fewer numbers of
subjects
• Its not expensive
• Test whether suspected cause
occur more frequently in those
with dx than those without
disease.
COHORT
• Proceed from cause to effect
• Start with people exposed to
risk factors
• Results are delayed.
• Involve large numbers of
subjects
• Its expensive
• Test whether dx vary more
frequently in those exposed
and those not similarly
exposed
17. Interventional Study
• Also known as experimental study
• It involves two groups
• One group is deliberately subjected to an
experience while the other is not
18. Epidemiological tools
• The basic epidemiological tools are:
- Rate
- Ratio and
- Proportion
• Proportions and rates are used to measure
disease burden
• Ratios are commonly used to measure
association between diseases and hypothesized
exposures
19. Proportions
• Usually expressed as
–a probability (0.0 and 1.0)
–a percentage (0% and 100%)
• consists of one count (numerator)
divided by another count
(denominator).
19
20. Proportions
• However,
– all the individuals in the numerator are also
included in the denominator,
– each individual in the denominator is at risk of
being in the numerator,
– all the individuals at risk of being in the numerator
in a group must be in the denominator.
20
21. Rate
• It measures the occurrence of some particular
event in a population during a given time
period.
• It indicate the change in some event that takes
place over a period of time.
• It comprises the following elements:
numerator, denominator, time specification
and multiplier.
22. Ratio
• The subjects of the numerator are different from
those in the denominator
• Not restricted to values between 0.0 and 1.0 as
are proportions (that is, can take any value)
• Commonly expresses as x:y
22
23. Uses
• To study historically the rise and fall of
diseases in the population
• Community diagnosis
• Planning and evaluation
• Completing the natural history of disease
• Searching for causes and risk factors
24. 24
Other uses of epidemiology
• Highlight international differences
• Describe regional problems
• Follow time trends
• Identify high risk groups
• Define priorities
25. Uses
In the community
• To study historically the rise
and fall of diseases in the
population
• Community diagnosis
• Completing the natural
history of disease
• Searching for causes and
risk factors
• Follow time trends
• Identify high risk groups
In the hospital
• Planning and evaluation
• Searching for causes and
risk factors
• Highlight international
differences
• Describe regional problems
• Follow time trends
29. Conclusion
• An epidemiological study well designed and
properly done provide useful and reliable
results and adds to the body of knowledge.
For evidence based medicine, we all need to
be involved in it.
