Descriptive Epidemiology in Public Health
MR OGUNDELE
Epidemiology
EPI
DEMO
LOGOS
Upon,on,befall
People,population,man
the Study of
The study of anything that happens to
people
“That which befalls man”
Descriptive studies
Descriptive
Individual
Case report
Case series
Cross sectional studies
Populations{Correlational studies}Descriptive Epidemiology
Study of the occurrence and distribution of disease
Terms:
Time
Place
Person
Descriptive Studies
Relatively
inexpensive
and less time-
consuming than analytic studies, they
describe,
Patterns of disease occurrence, in terms of,
Who gets sick and/or who does not
Where rates are highest and lowest
Temporal patterns of disease
Data provided are useful for,
Public health administrators (for allocation of
resources)
Epidemiologists (first step in risk factor determination)
Descriptive Studies
Case reports
Case series
Cross sectional studies
Correlational studies
CASE REPORT AND CASE SERIES
Case reports and case series represent the most basic type
of study design, in which researchers describe the
experience of a single person
(
case report
)
or
a group
of people
(
case series
).
Typically, case reports and case series describe individuals
who develop a particular new disease or condition.
The
identification of a new or recurring health
problem
often begins with a
case report
or
case series
CASE REPORT AND CASE SERIES
Example:
A case series describes 20 women who
develop cervical cancer; 9 of these women report at
least once weekly ingestion of foods packaged with
aluminum foil. Urine testing confirms the presence of
aluminum among all 9 case women.
NB
: it is tempting to conclude that aluminum foil
causes cervical cancer.
Case Reports (case series)
Limitation
1) Case reports / case series
lack denominator data
that are necessary to calculate the
rate of
Disease
:
Disease rates are needed for comparison with
historically reported disease rates, or with rates from a
selected comparison group. Unfortunately, obtaining
the necessary denominator data may not be easy.
2) Case report / case series report data
lack comparison
group.
3)
Case reports / case series studies often
describe
highly select individuals
who may not represent the
general population.
SCENARIO 1
1) The classic description of a series of infants born with
congenital cataracts
, some with additional cardiac
abnormalities, in Australia in 1941. This led Dr N. M.
Gregg in Sydney to postulate a causal link between a
severe epidemic of
rubella
(German measles) that
had occurred six to nine months before the children
were born and the subsequent abnormalities (Gregg,
1941).
NB:
It is now well known that if a woman develops
rubella during pregnancy it may affect her unborn
baby.
SCENARIO 2
2) A case report published in the UK in 1961 described
the development of a pulmonary embolism in a 40-
year-old pre-menopausal woman, five weeks after she
had started using an oral contraceptive (OC) to treat
endometriosis (Jordan, 1961). The author suggested
that it might have been caused by the OC, particularly
since it was a new exposure at that time.
NB:
A report of one case could not provide conclusive
evidence that it was the OC. These have consistently
shown that there is an association between the use of
OCs and the risk of this condition.
Cross-Sectional Studies
(prevalence studies)
A cross-sectional study refers to a study design in
which
ascertainment of the exposure and the
outcome occurs simultaneously
. Measuring the
exposure and outcome at the same time implies that
there
is
no follow-up time.
Cross-Sectional Studies
In cross sectional studies, information about the status
of an individual with respect to the presence or
absence of exposure and disease is assessed at a
point
in time
.
The
point in time
may be as short as few minutes or
as long as two or three months. The time frame of
"point in time" is based on the speed of data
collection.
Cross-Sectional Studies (prevalence studies
)
Measures disease and exposure simultaneously in
a well-defined population
Advantages
They cut across the general population, not simply those
seeking medical care
Good for identifying prevalence of common outcomes,
such as arthritis, blood pressure or allergies
are less expensive & easier to conduct
Limitations
Cannot determine whether exposure preceded disease
It considers prevalent rather than incident cases, results
will be influenced by survival factors
Correlational Studies (Ecological Studies)
The simplest type of study is an ecologic study (also
called a correlation study). In this type of study
information is collected not on individuals but on
groups of people
. The unit on which measurement is
made may be for example schools, towns, countries,
etc.
They use aggregate data
and do not measure
outcomes and risk factors.
They are used to compare different groups, such as
populations from different regions or countries, or
groups from different types of employment
Correlational Studies (Ecological Studies)
Uses measures that represent characteristics
of entire populations
It describes outcomes in relation to age, time,
utilization of services, or exposures
ADVANTAGES
We can generate hypotheses for case-control
studies and environmental studies
We can target high-risk populations, time-periods,
or geographic regions for future studies
Correlational Studies
LIMITATIONS
Because data are for groups, we cannot link disease and
exposure in individual
Data represent average exposures rather than individual
exposures, so we cannot determine a dose-response
relationship
Caution must be taken to avoid drawing inappropriate
conclusions, or
ecological fallacy
Correlational Studies
Ecologic
(
correlation
) studies can be used in
determining association
plot
:
disease (population) burden [ Y axis ]
vs.
prevalence of “risk factor” [ X axis ]
e.g. contraceptives vs. Breast cancer
correlation coefficient : r ; + 1 to -1
Descriptive epidemiology involves the study of disease occurrence and distribution in populations. It focuses on describing patterns of disease occurrence based on who gets sick, where rates are highest and lowest, and temporal patterns of disease. Descriptive studies are essential for public health administrators to allocate resources effectively and for epidemiologists to identify risk factors in disease prevention.
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Presentation Transcript
Epidemiology EPI DEMO LOGOS Upon,on,befallPeople,population,man the Study of The study of anything that happens to people That which befalls man
Descriptive studies Descriptive Individual Case report Case series Cross sectional studies Populations{Correlational studies}
Descriptive Epidemiology Study of the occurrence and distribution of disease Terms: Time Place Person
Descriptive Studies Relatively consuming than analytic studies, they describe, inexpensive and less time- Patterns of disease occurrence, in terms of, Who gets sick and/or who does not Where rates are highest and lowest Temporal patterns of disease Data provided are useful for, Public health administrators (for allocation of resources) Epidemiologists (first step in risk factor determination)
Descriptive Studies Case reports Case series Cross sectional studies Correlational studies
CASE REPORT AND CASE SERIES Case reports and case series represent the most basic type of study design, in which researchers describe the experience of a single person (case report) or a group of people(case series). Typically, case reports and case series describe individuals who develop a particular new disease or condition. The identification of a new or recurring health problem often begins with a case report or case series
CASE REPORT AND CASE SERIES Example: A case series describes 20 women who develop cervical cancer; 9 of these women report at least once weekly ingestion of foods packaged with aluminum foil. Urine testing confirms the presence of aluminum among all 9 case women. NB: it is tempting to conclude that aluminum foil causes cervical cancer.
Case Reports (case series) Limitation 1) Case reports / case series lack denominator data that are necessary to calculate the rate ofDisease: Disease rates are needed for comparison with historically reported disease rates, or with rates from a selected comparison group. Unfortunately, obtaining the necessary denominator data may not be easy. 2) Case report / case series report data lack comparison group. 3) Case reports / case series studies often describe highly select individuals who may not represent the general population.
SCENARIO 1 1) The classic description of a series of infants born with congenital cataracts, some with additional cardiac abnormalities, in Australia in 1941. This led Dr N. M. Gregg in Sydney to postulate a causal link between a severe epidemic of rubella (German measles) that had occurred six to nine months before the children were born and the subsequent abnormalities (Gregg, 1941). NB: It is now well known that if a woman develops rubella during pregnancy it may affect her unborn baby.
SCENARIO 2 2) A case report published in the UK in 1961 described the development of a pulmonary embolism in a 40- year-old pre-menopausal woman, five weeks after she had started using an oral contraceptive (OC) to treat endometriosis (Jordan, 1961). The author suggested that it might have been caused by the OC, particularly since it was a new exposure at that time. NB: A report of one case could not provide conclusive evidence that it was the OC. These have consistently shown that there is an association between the use of OCs and the risk of this condition.
Cross-Sectional Studies (prevalence studies) A cross-sectional study refers to a study design in which ascertainment of the exposure and the outcome occurs simultaneously. Measuring the exposure and outcome at the same time implies that there is no follow-up time.
Cross-Sectional Studies In cross sectional studies, information about the status of an individual with respect to the presence or absence of exposure and disease is assessed at a point in time. The point in time may be as short as few minutes or as long as two or three months. The time frame of "point in time" is based on the speed of data collection.
Cross-Sectional Studies (prevalence studies) Measures disease and exposure simultaneously in a well-defined population Advantages They cut across the general population, not simply those seeking medical care Good for identifying prevalence of common outcomes, such as arthritis, blood pressure or allergies are less expensive & easier to conduct Limitations Cannot determine whether exposure preceded disease It considers prevalent rather than incident cases, results will be influenced by survival factors
Correlational Studies (Ecological Studies) The simplest type of study is an ecologic study (also called a correlation study). In this type of study information is collected not on individuals but on groups of people. The unit on which measurement is made may be for example schools, towns, countries, etc. They use aggregate data and do not measure outcomes and risk factors. They are used to compare different groups, such as populations from different regions or countries, or groups from different types of employment
Correlational Studies (Ecological Studies) Uses measures that represent characteristics of entire populations It describes outcomes in relation to age, time, utilization of services, or exposures ADVANTAGES We can generate hypotheses for case-control studies and environmental studies We can target high-risk populations, time-periods, or geographic regions for future studies
Correlational Studies LIMITATIONS Because data are for groups, we cannot link disease and exposure in individual Data represent average exposures rather than individual exposures, so we cannot determine a dose-response relationship Caution must be taken to avoid drawing inappropriate conclusions, or ecological fallacy
Correlational Studies Ecologic ( correlation ) studies can be used in determining association plot : disease (population) burden [ Y axis ] vs. prevalence of risk factor [ X axis ] e.g. contraceptives vs. Breast cancer correlation coefficient : r ; + 1 to -1
