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October 21 2004
Epi 511
What is this? How can you use it to
explain occurrence of WNV?
Host
Vector
Agent
Environment
Herd Immunity
• Why is it important for vaccine programs?
• What types of “agents” work best to
establish herd immunity?
• Why do you need a flu shot almost every
year?
Where is the incubation period?
Observable
illness
Exposure
Treatment
Infection
Pre Clinical
period
Clinical Period
Outcome
Infectious disease
• Is the “Attack rate” more like prevalence or
incidence rate?
• Give an example of primary prevention and
tertiary prevention.
• Does “secondary attack rate” refer to initial
disease cases becoming infected with a
second disease? Explain.
• Endemic : epidemic :: usual : ?
Mortality measures
• If 4739 pedestrian vs motor vehicle deaths
occurred in 2002, and there were known to
be 78,000 motor vehicle accidents in that
year. What is the case fatality rate?
Personalities:
What did they contribute to Epi?
•
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John Graunt
William Farr
John Snow
Joe Goldberger
Edgar Sydenstryker
Study designs
• Describe an Ecologic study of the association
between fish consumption and stroke.
• Describe a Case-control study of the association
between fish consumption and stroke.
• Describe a Cohort study of the association
between fish consumption and stroke.
• Describe a Randomized trial of the association
between fish consumption and stroke.
Questions about designs
• Give an example of “ecologic fallacy” from
the study of fish and stroke.
• Cross-sectional studies are most valuable in
establishing temporal relationships, why or
why not?
Disease occurrence
• How might you determine the prevalence of
Parkinson’s disease in Seattle as of July 1, 2003?
• How would you determine the incidence of ALS
per 100,000 population in King County, in 2003?
In 1999?
• Suppose the incidence of Pancreatic ca and
Multiple Sclerosis were similar, why might their
prevalence be similar or dissimilar?
Standardization
• Comparing mortality rates from diarrheal
disease in Somalia relative to Connecticut
results in an SMR of 437. What does that
mean.
• Why would we want to compute SMR?
• Is SMR most frequently associated with
Direct or Indirect standardization?
Occurrence
• In Milwaukee, the proportion of deaths due to
alcoholism it greater than it is in Cleveland.
Therefore, persons in Milwaukee are at greater
risk of death from alcoholism? Why or why not.
• MS is more prevalent in latitudes farther from the
equator. Therefore your risk of MS is greater in
Seattle than in L.A. Why/Why not
Rates
CIt = 1 - e
-IDD(t)
What does this formula calculate?
Why is it useful?
Confidence intervals
• A confidence interval expresses a summary of the
data in original units of measurement.
• It reflects the variability in the data, the sample
size, and the actual effect size observed.
• Includes the “true” value with x% confidence
• Agree or disagree with any of the above?
Why?
Design, Incidence, RR, AR?
Exposed
Not exposed
Subject Develop Person
disease? -years
ID #
Subject Develop Person
ID#
disease? -years
E001
No
6.5
N010
No
6.5
E002
Yes
1.5
N011
Yes
5.0
E003
Yes
5.5
N012
No
6.5
E004
No
3.5
N013
No
3.5
E005
No
2.5
N014
No
4.0
E006
Yes
2.0
N015
Yes
2.5
E007
Yes
6.0
N016
No
6.5
E008
No
1.5
N017
No
5.0