epidemiology - cracksmod · descriptive epidemiology : describes the distribution of disease in a...
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EpidemiologyThe study of distribution and determinants of
disease frequency in human population .
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epidemiology is divided into :
1. Descriptive epidemiology .
2. Analytic epidemiology .
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Descriptive epidemiology :
Describes the distribution of disease
in a population , and observing the
basic feature of its distribution in
terms of person , place and time ,
the typical study design for
descriptive study is ( cross-sectional
study) .
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many types of descriptive
studies:
1. on populations ( correlational
studies)
2. on individuals :
a. case reports .
b. case series.
c. cross sectional surveys.
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Descriptive studies raise the
question of association rather than
proving it.
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Analytic epidemiology :
Testing a specific hypothesis about the relationship of a disease to putative cause , by conducting an epidemiologic study that relate the exposure of interest to the disease of inertest .
typical study designs: cohort , case-control studies . also we have intervention studies or what called clinical trial or experimental studies.
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The basic triad of descriptive
Epidemiology the three essential characteristics of
disease we look for in descriptive
epidemiology are:
1. person .
2.place.
3.time.
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Person
Who is getting the diseases ?
many variables are involved and
studied , but factors like sex , age
and race have a major effect .
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Characteristics of person :
. Age
. Sex (gender)
.Ethnic group
.Socioeconomic status
.Nativity
.Religion
.marital status
.Occupation
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Place
.Where are the rates higher ? lower?
. Geographic location of source
.Geographic location of reservoir
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5 criteria of place :
1. high rate observed in all ethnic group in the area .
2. high rate NOT observed in persons of similar groups inhabiting other areas .
3. Healthy persons entering area get ill at same frequency .
4. people who leave do NOT show similar levels .
5. Similar levels of infestation in other species ( if zoonotic disaes).
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characteristics relating to place:
. International
.Variation within countries
Urban-rural
Local
.Building maps
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Interaction of time and place :
1. Time-place clustering .
2. Migration .
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Time
.When does the disease occur ?
"Temporal "
Range from hours to decades
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Characteristics relating to time :
1. Secular change (long-term) .
2.Point epidemics (short-term) .
3. Cyclic trends.
4.Seasonal variation.
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.Descriptive epidemiology is a
necessary antecedent of analytic
epidemiology
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To undertaken an analytic
epidemiology study you must first :
. know where to look
.know what to control for
.be able to formulate hypotheses
compatible with laboratory
evidence.
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A common error in epidemiology is moving to
analytic epidemiology without having a solid
base in the descriptive epidemiology of the
condition .
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Population at risk
It is a frequent term in the
epidemiology that denotes to the
by certain a characteristic sharing of
population subgroup that put them
at increased risk for development of
a health outcome ( disease , death ,
...)
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so the population at risk is :
any group that is susceptible and
exposed to risk factor .( they should
have both criteria to be population
at risk) .
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In previous definition , we have the word " characteristic " and there are 3 types of characteristics :
1. Biological : which includes the sex (gender) , age , genetic factors, .....
2. Environmental : such as being nearby chemical factories or near polluted water resources.
3. Socioeconomical : such as nutritional status , poverty , ....
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Risk : a term which denotes to the more probability for having an outcome .
Risk factor : a condition , physical characteristics or behavior that increase the probability that a currently healthy individual will develop a particular disease .
Outcome : it's the notement at the disease status , so it may be death or accident or handicaps.
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Types of risk factors
1/ Environmental risk factors :
they are found in the physical
environment ( infectious organisms,
pollutant , toxins , and drugs ) ,
2/ Behavioral ( life habit) risk factors
include such behavior as smoking
and failing to observe occupational
safety precaution .
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Types of risk factors
3/ Social risk factors : like divorce , death of family member and job loss.
4/ Genetic risk factors : are inherited factors ex.( familial hypercholesterolemia ) which increase the risk of coronary artery disease .
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Relationship of risk factors to
disease
A risk factor may be a causal factor
of disease or merely a marker for
increased probability of disease , for
example: while poor prenatal care
and drug use constitute causal
factors for neonatal mortality , the
socioeconomic status would be
consider a marker for neonatal
mortality .
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Thank you