The STUDY of the DISTRIBUTION & DETERMINANTS of HEALTH-RELATED STATES in specified POPULATIONS, and the application of this study to CONTROL of health problems.

1. Dr. Dalia El-Shafei
Assistant Professor, Community Medicine
Department, Zagazig University
http://www.slideshare.net/daliaelshafei

2.  Epidemiology is derived from the Greek,
Epidemiology is the basic science
of Public Health

3. Definition of Epidemiology
The STUDY of the DISTRIBUTION &
DETERMINANTS of HEALTH-RELATED
STATES in specified POPULATIONS, and the
application of this study to CONTROL of health
problems."

4.  Is the basic science of public health
 Provides insight regarding the nature,
causes, and extent of health & disease
 Provides information needed to plan &
target resources appropriately
So, Epidemiology

10. Non-experimental
“Observational” studies:
-Investigator measures
but does not intervene.
-The investigator observes
natural course of events,
observing who is exposed
& who is not, who is
diseased & who is healthy.
-The non-experimental
studies can be either
descriptive or analytical.
Experimental
“Interventional” studies:
-Active trial to change
disease determinant by the
investigator who controls
the exposure.
-Investigator allocates the
exposure & follows the
subjects.
-Participant are identified
on the basis of their
exposure status & followed
to determine whether they
develop the outcome or not.
Epidemiological studies

12. Epidemiological
Studies
Observational
“Non-
experimental”
Descriptive
Population
Correlational
studies
Individuals
Cross
sectional
surveys
Case reports
Case series
Analytical
Comparative
cross-
sectional
Case-control
Cohort
Prospective
Retrospective
Experimental
Clinical trials
Community
trials
Field trials

15. Descriptive Epidemiological studies
To Know the situation: (what is the
problem? What are its manifestations?)
Or
 To Describe the general characteristics
of a disease /or health problem in relation
to PPT (Person– Place –Time).

16. □ Person: Who is getting sick?
□ Place: Where is the sickness occurring?
□ Time: When is the sickness occurring?
“PPT = Person, Place, Time”

17. Epidemiological
Studies
Observational
“Non-
experimental”
Descriptive
Population
Correlational
studies
Individuals
Cross
sectional
Case reports
Case series
Analytical
Comparative
cross-
sectional
Case-control
Cohort
Prospective
Retrospective
Experimental
Clinical trials
Community
trials
Field trials

18. & Case Series

19. 1- Case Report:
Example:
Intestinal obstruction was reported in a young child..
Documents showed that this child received Rota virus
vaccine 3 months ago. A detailed report about this unusual
event & exposure was published in a medical journal. The
investigator formulated a hypothesis that Rota virus vaccine
may have been responsible for the rare occurrence of this
event.

24. Features of the Case Report:
 It consists of a careful & detailed report (published
in medical journals) by one or more clinicians of
unusual medical condition.
 It represents the 1st clue in the identification of a new
disease.
 It leads to formulation of a new hypothesis.

26. 2- Case Series:
It is the only study which depends on Routine Surveillance.
Example of the case series study:
• During 1950 , 8 cases of cancer lung were admitted to different
hospitals during the same period of time. Taking history from these
patients showed that they were miners. This unusual circumstance
suggested that the miners may been exposed to something.
Investigating this circumstance showed high concentration of radon
gas. A hypothesis was formulated that lung cancer is related to
exposure to radon.

30. The benefits of case report & case series:
They identify a new case and/ or an unusual variation
of a disease occurrence.
• Formulate a new hypothesis for disease
occurrence.
•Trigger “stimulate start of analytic studies to be
conducted to identify risk factors of disease”.
• Modification of case series to be a case-control
study by using a comparison group.

31. The limitations of the case report & case series:
o For the case report, the presence of any exposure
may be coincidental because it is based on a
single experience .
o Lack of the comparison group in case series can
either obscure the relationship or suggest an
association which is not actually exist.
o Both of them cannot be used to show the causal
association i.e. can not be used to test the
hypothesis.

33. Correlation study: ( Ecological study)
 The source of data is the entire population .
 It compares disease frequencies:
- between different population during the
same period of time Or
- In the same population at different in time .
 It compares 2 quantitative variables.

43. Correlation between one of climatic indicator
(Temp.) & frequency of cerebrovascular storks.
Figure 1 shows the correlation between the
average regional temp. & the frequency of
CVSs in different countries. Countries with the
highest average temp. have the highest rates of
CVSs and vice versa.

44. 100 The average regional temp. & the frequency of CVSs
80
+ve Correlation (r = +1)
60
40
20
0
10°C 15°C 20°C 25°C 30°C 35°C 40°C
The Average Regional Temperature

45. Example 2:
The average number of mammography carried for
women above 50 years of age per year & the
mortality from cancer breast.
This can be presented by the following figures.

46. The average number of mammography per year for woman
above 50 & the mortality from cancer breast
100 Negative Correlation (r = -1)
80
60
40
20
0
3 4 5 6 7 8 9
The average number of mammography per year for woman above 50

47. The advantages of the correlation study:
1- Formulates new hypothesis.
2- Quick & Cheap.

48. The limitations of correlation studies:
1. As the value of exposure is quantified by the
average, it is impossible to link the exposure & the
disease in a particular individual. It is not possible to
tell that the person who gets cerebro-vascular stroke
is the one who is exposed to high temperature.
2. They cannot be used for testing the hypothesis.
3. Lack of the ability to control for the effects of the
confounding factors.

50. Confounding factors:
These are factors other than the studied one
that disturb the relation between the studied
exposure and the disease of interest.
For example: The association between the
average family size and the frequency of iron
deficiency anemia may be due to other factors
such as the pattern of diet, the infectious
diseases , the socioeconomic conditions and
parasitic infections.

51. Impacts of the Confounding Factors
Large Family size
(Exposure)
Iron deficiency anemia
(condition)
Parasitic Infection
Pattern of Diet
Mothers Awareness
Mothers Education
(Confounding factors)

60. Cross sectional study (Prevalence study):
Population Sample
Without Exposure & without disease
Without Exposure & with disease
With Exposure &without disease
With Exposure & with disease

61. The uses of cross-sectional study:
 Estimation of prevalence rate of disease or
any health related phenomena.
It leads to formulation of hypothesis.
It is suitable for chronic diseases with long
latency.
 Quick & cheap, compared to case-control
& cohort studies.

62. The Limitations of the cross-sectional study:
 Can’t be used to test hypothesis (chicken-egg
dilemma).
 Deals with survivals only but those who died,
cured or migrated are not included.
 Can’t be used in acute diseases of short duration.
 Not suitable for rare diseases (Compared with the
case control study).

63. Example:
During the year 2004 , a representative sample of
secondary school pupils in a city x (n=400) were
asked about consumption of high caloric diet &
examined to detect obesity.
Questions:
Draw the flow chart.
Tabulate the data.
Write the title of the table.

64. No consumption of high
Caloric diet without obesity
n=304
No consumption of high
Caloric diet with obesity
n=16
Consumption of high
Caloric diet without obesity
n=60
Consumption of high
caloric diet with obesity
n=20
Secondary
school pupils
Sample
n=400
The flow Chart:

65. Distribution of the studied sample of secondary school
pupils in the city X during the year 2004 according to
consumption of high caloric diet & obesity.
Consumption of
high caloric diet
With
obesity
Without
obesity
Total
Yes 20 60 80
No 16 304 320
Total 36 364 400

66. Prevalence of obesity among those consumed high caloric diet (P1 ) =
20 X 100 = 25%
80
Prevalence of obesity among those don’t consume high caloric diet
(P2) =
16 X 100 = 5%
320
The prevalence rate =
The total number of all cases (old and new) in certain area at a given time X 100
The total number of population in the same area and time

67. Population
Village (Sample)
No HCV,
no Bl.T
(D) (E)
HCV, Bl.T.
(D) (E)
No HCV, Bl.T.
(D) (E) HCV, no Bl.T.
(D) (E)
Hepatitis C infect. & Blood Transfusion
4 different outcomes
Cross-Sectional Design

68. Population
Village
(n= 200)
Not D, not E
120
Not D, E
40
D, not E
10
D, E
30
Descriptive Data: Prevalence Rate
Prevalence of HCV in village: 40/ 200 = 20%
Prevalence among males, among females….
Prevalence among different age groups…….
Prevalence of blood transfusion: 70/200 = 35%

69.  Prevalence of HCV among those receiving
blood transfusion 30/70 = 42.8%
 Prevalence of HCV among those not receiving
blood transf.: 10/130 = 7.6%

70. Exercise1:-
Description of 35 patients with thyroid cancer
are regarding past history of exposure to
radiation and response to surgical treatment
Feedback:-
Case series

71. Exercise 2:-
A 39-year old man who presents with mild sore
throat, fever, malaise and headache was treated with
penicillin for presumed streptococcal infection.
He returned after a week with hypotension, fever and
abdominal pain .
A diagnosis of Rocky Mountain spotted fever was
made and he responded good to chloramphenicol.
Feedback 2:-
Case report

72. Exercise 3:-
500 patients were classified according to their
body mass index (obese or not) and
simultaneously according to having knee
osteoarthrosis
Feedback of Exercise 3:-
Cross sectional study