descriptive epidemiology, classification, examples,

2. DESCRIPTIVE EPIDEMIOLOGY
-DR KARISHMA S HALAGERI
2ND YR PG
DEPT OF PUBLIC HEALTH DENTISTRY

3. CONTENTS
• Introduction
• History
• Activities in epidemiology
• Classification of epidemiological methods.
• Aims of descriptive epidemiology.
• Steps in descriptive studies
• Uses of descriptive epidemiology.
• Types of descriptive studies
• Case report
• Case series

4. • Ecological studies
• Cross sectional studies
• Longitudinal studies
• Comparison of epidemiologic descriptive study
• Errors in report of descriptive epidemiologic study
• Conclusion
• References
CONTENTS

5. • Human health and disease are unequally distributed throughout populations.
• This generalization applies to differences among population groups
subdivided according to age and other demographic characteristics among
different countries, within a single country, and overtime.

6. • Epidemiology is a core subject required in public health and public
health programs and provides information about public health
problems and causes to it.
• Provides insight regarding the nature, causes, and extent of health &
disease
• This information is used to improve the health and social conditions of
the people.

7. EPIDEMIOLOGY
“The study of occurrence and
distribution of health related
events, states and processes in
specified populations, including
the study of determinants
influencing such processes, and
application of this knowledge to
control relevant health problems.”
- John M Last (1988).
History
Dates back to 3rd century BC
Foundations was laid in 19th century
Landmark in epidemiology: Cholera
John Snow: Father of epidemiology

8. THE CHOLERA STUDY (1854)
The broad street pump

9. Pessimist: The glass is half empty.
Optimist: The glass is half full.
Epidemiologist: As compared to what ?

10. ACTIVITIES IN EPIDEMIOLOGY
• An epidemiologist studies the occurrence of disease or other health-
related events in specified populations, practices epidemiology and
controls disease.
Identify risk factors for
disease, injury and
death
Describe natural
history of disease
Identify individuals and
populations at greatest
risk of disease
Monitoring disease ,
evaluating the efficacy
and effectiveness of
prevention and
treatment programs
Assisting in carrying
out public health
programs

11. • Study design is a program that directs the researcher along the path
of systematically collecting, analyzing and interpreting data.
• It is formal approach of scientific or scholarly investigation.
• The method may involve observational or experimental assessment.

12. CLASSIFICATION OF EPIDEMIOLOGIC
METHODS
case
crossover
Nested case
control

14. • First phase of an epidemiologic investigation.
Concerned with
Observing the distribution of disease in population and
identifying the characteristics associated with it.

15. • When specific diseases, adverse health outcomes, or other health
characteristics are more prevalent among one group than among another,
the logical question that follows is ‘’why?’’
• The answer to the question one must consider 3 W’s
Who was
affected ?
Where did the
event occur ?
When did the
event occur?

16. • The field of descriptive epidemiology classifies the occurrence of disease
according to the
Descriptive epidemiology involves observation, definitions,
measurements, interpretations, and dissemination of health
related states/ events by person, place and time.

17. AIMS OF DESCRIPTIVE EPIDEMIOLOGY
Permit evaluation of trends in health and disease
Provide a basis for planning, provision, and evaluation
of health services
Identify problems to be studied by analytic methods and suggest areas
that may be fruitful for investigation

19. PROCEDURES IN DESCRIPTIVE STUDIES
1) Defining the population to be studied
2) Defining the disease under study
3) Describing the disease by time place person
4) Measurement of disease
5) Comparing with known indices
6) Formulation of an etiological hypothesis

20. STEP 1: DEFINING THE POPULATION
• Descriptive studies are investigations of population.
• A defined population should not only be in terms of total number, but also
in terms of age, sex, occupation, cultural characters, hospital
patients, school children and similar information needed for study etc.

21. • The defined population-
i) Could be a whole geographic region or a representative sample
ii) Could be a specially selected group- based on age , sex, occupation,
etc
iii) Should be large enough so that it is meaningful
iv) Should be stable without migration into or out of the area.
v) Should not be different from other communities in the region.
The concept of defined population is crucial in
epidemiological studies.
It provides denominator for calculating rates
which are essential to measure the frequency of
disease and study its distribution and its
determinants

22. STEP 2: DEFINING THE DISEASE UNDER STUDY
• The epidemiologist defines the disease which can be measured and identified
in the defined population with a degree of accuracy.
• This is different from the clinician’s definition of a disease.
• Epidemiologist main concern is to, needs a definition that is both precise and
valid.
• Diagnostic methods for use in epidemiological studies must be acceptable to
the population to be studied, and applicable to their use in large population.
This is required so as to enable
observer to identify those who have
the disease from those who do not
have.

23. FOR EXAMPLE :
DEFINITION
• Gingivitis
inflammation of the gingiva
• Dental caries
microbial disease of the calcified
tissues of the teeth, characterized by
demineralization of the calcified tissues
and destruction of the organic
substance of the teeth.
OPERATIONAL DEFINITION
• Gingivitis
gums appear red and puffy and usually
gingival bleeding in one or more sites
after gently probing the gingival sulcus .
• Dental caries
The lesion is clinically visible and obvious.
Explorer tip can penetrate deep into soft
yielding material. Explorer tip resists
removal after moderate to firm pressure.

24. STEP 3: DESCRIBING THE DISEASE
• Primary objective of descriptive epidemiology :
Describe the occurrence and distribution of disease by time , place and
person and identifying those characteristics associated with presence
and absence of disease in individuals.
This involves systematic collection and analysis of data.

25. Time
Distribution
Short term
fluctuations
Periodic
fluctuations
Long term or
Secular trends
Cyclic
Trend
Seasonal
Trend
Common
source
Propagated
Slow
(modern)
Person to
person
Arthropod
vector
Animal
reservoir
Single/point exposure
Continuous/multiple
exposure
1)Time Distribution

26. EPIDEMICS
• Epidemic may result from exposure to common source at a point in time, or continuous exposure over days,
weeks, years.
• Epidemic may result from exposure propagated through gradual spread from host to host or originate from
common source and then secondary spread, be communicated from person to person.
Epidemics is the occurrence of cases of an
illness, specific health related events clearly
in excess of normal expectancy in a
community or a region
Outbreak = epidemic
confined to localized
area

27. ENDEMICS AND PANDEMICS
• Endemics – refers to the ongoing, usual or constant presence of
disease in a community or among a group of people; a disease is said
to be endemic when it continually prevails in a region.
• Pandemic – is an epidemic affecting or attacking the population of an
extensive region, country or continent.

28. • A graph of time distribution of epidemic cases is called epidemic curve .
Time relationship with exposure to
suspected source .
A cyclic or seasonal pattern
suggestive of a particular infection,
and a common source or
propagated spread of the disease.

29. A) SHORT TERM FLUCTUATIONS
• An epidemic is the best known short term fluctuation. It is defined as “
The occurrence in community or region of cases of an illness or
other health related events clearly in excess of normal expectancy”.
Common source
epidemics
• Single/point
exposure.
• Continuous/multipl
e exposure
Propagated
epidemics
• Person to person
• Arthropod vector
• Animal reservoir
Slow(modern)
epidemics
Describing the disease Time distribution

30. I) COMMON SOURCE EPIDEMICS
1)Single exposure-
• It can occur due to an infectious agent or as a result of
contamination of the environment and develops within one
incubation period. Eg : Bhopal gas tragedy, Minamata disease, food
poisoning .
• The epidemic curve rises and falls rapidly, usually has one peak
• It tends to be explosive (i.e. clustering of cases within a short time)
Describing the disease Time distribution Short term fluctuations

31. Describing the disease Time distribution Short term fluctuations

32. 2) CONTINUOUS EXPOSURE -
• It is when the exposure from the same source is prolonged and the
epidemic continues over more than one incubation period.
• The epidemic reaches a sharp peak, but tails off gradually over a
longer period of time.
• Eg: A well of contaminated water food; water borne cholera.
Fluorosis .
Describing the disease Time distribution Short term fluctuations

33. II) PROPAGATED EPIDEMICS
• Types- person to person, arthropod, animal
• The epidemic shows gradual rise and tails off over a much longer
period of time
• It is more likely to occur where there is
i) regular supply of new susceptible individuals- Births, Immigrants
lowering herd immunity
ex:Hepatitis A , poliomyelitis, Measles
Describing the disease Time distribution

34. Course Of A Typical Propagated Epidemic

35. B) PERIODIC FLUCTUATIONS
1) Seasonal trend-
• Seasonal variation is characteristic of many communicable diseases. Eg: Acute
sinusitis, Measles, upper respiratory tract infections(seasonal rise during winter),
Malaria, etc.
-Outbreaks of dengue in India starting from july peaking in October, November
coinciding late summer and rain
• Non-infectious diseases and conditions may sometimes exhibit seasonal
variation.
Eg: Sunstroke, hay fever.
seasonal variation in bruxism and its symptoms with a peak in the winter months.
[Kardeş S, Kardeş E. Seasonality of bruxism: evidence from Google Trends. Sleep and Breathing. 2019 Jun 1;23(2):695-701.]
Describing the disease Time distribution

36. 2) CYCLIC TREND-
• Some diseases occur in cycles spread over short periods of time
(days, weeks, months or years) .
Eg: Influenza pandemics are known to occur at intervals of 7-10yrs due
to antigenic variations.
-recurrent apthous ulcers,
-oral thrush .
• Non-infectious conditions may also occur in this trend.
Eg: Automobile accidents more frequent on weekends.
Describing the disease Time distribution Periodic fluctuations

37. C) LONG TERM TRENDS
• It refers to changes in the occurrence of disease over a long period
of time.
Eg: Coronary disease, diabetes, dental caries showing consistent
upward trend and a decline in polio in developing countries during the
past 50 yrs.
Describing the disease Time distribution

38. WHY WE SHOULD KNOW TIME TRENDS?
• To know diseases which are increasing or decreasing &
emerging health problems.
• Can frame effective measures to control the diseases
• Formulate etiological hypothesis.
• Provide guidelines to health administrator in matters of
prevention or control of disease.

39. 2) PLACE DISTRIBUTION
1. International variation 2. National variation
3. Rural – Urban variation 4. Local distribution
Place variations
Describing the disease

40. A) INTERNATIONAL VARIATION
• Descriptive studies have shown that the pattern of a disease is not
the same everywhere
• Eg: Cancer of the stomach is very common in Japan, but unusual in
the US.
• Oral cancer is common in India,
but less seen in China
Global data on incidence of oral cancer (maps)-
WHO
Describing the disease Place distribution
These variations have stimulated epidemiologists
to search for cause-effect relationship between
environmental factors and disease.

41. B) NATIONAL VARIATION
• There are variations in disease occurrence within countries.
• Eg: The distribution of endemic goitre, fluorosis, malaria,
nutritional deficiencies show variations in their distribution in India.
Describing the disease Place distribution

42. C) RURAL-URBAN VARIATIONS
• Due to differences in population density, levels of sanitation, deficiencies of
medical care, education and environment factors, there exists a rural-urban
variation
• Chronic bronchitis, cardiovascular diseases, accidents, dental caries are more
frequent in urban than rural areas.
• Skin and zoonotic diseases and soil transmitted helminths
Oral submucous fibrosis , periodontal disease may be more frequent in rural than
urban areas.
Describing the disease Place distribution
These variations may be due to differences in population density, social class, deficiency in medical
care, education and environmental factors.
Epidemiologist seeks to define groups which are at higher risk for
particular diseases, and provides guidelines to the health administrator
for their prevention and control.

43. • These variations can be studied with the help of “spot or shaded”
maps. If the map showed clustering, it may suggest a common
source of infection.
• Eg: Study of Cholera epidemic by John Snow in 1854
D) LOCAL DISTRIBUTIONS
Describing the disease Place distribution

44. STUDY BY JOHN SNOW, 1854
This pump was
later suspected and
proved to be a
source of infection
Spot map of deaths from cholera in
Golden Square area,

45. The epidemiologist is interested in geographic variations in disease occurrence
Geographic distribution may provide evidence of the source
of disease and its mode of spread.
Describing the disease Place distribution
The geographic distribution of disease my change , if
changes occur in the agent, host and environmental
factors.
Mode of living and environmental factor vary from country
to country, one would expect to find differences in the
geographic distribution and frequency of disease.

46. 3) PERSON DISTRIBUTION
• The disease can be characterized by defining a person who develops
a disease based on age, sex, occupation, marital status, social
factors, habits and other host factors.
• These factors does not necessarily represent etiological factors, but
contribute to understand natural history of disease.
Describing the disease

47. A) AGE
• Certain diseases are more frequent in certain age groups than others.
• Eg: Measles in childhood, cancer in middle age and atherosclerosis in
old age.
• Dental caries more seen in school children
• Many chronic and degenerative diseases show a progressive increase
in prevalence with advancing ages.
Eg: periodontal diseases.
Describing the disease Person distribution

48. BIMODALITY
• There may be two separate peaks instead of one in the age
incidence curve of a disease. This is known as bimodality as seen in
Hodgkin’s lymphoma, breast cancer.
• It indicates that there are two different sets of causative factors
even though the clinical and pathological
manifestations of the disease
is the same in all ages.
Describing the disease Person distribution

49. B) SEX
• Variations occur due to-
1) Biologic difference like sex linked genetic
inheritance
2) Cultural and behavioral differences
between the sexes in social settings.
Eg: 4:1 male to female ratio in
lung cancer due to cigarette smoking.
Describing the disease Person distribution
World Cancer Report 2014.

50. C) ETHNICITY
• Differences in racial and ethnic origin.
• Eg: Tuberculosis, sickle cell anemia
D) MARITAL STATUS
• In a study, the mortality rates were lower for married people than unmarried of
same age and sex.
• Marital status can be risk factor for some diseases and conditions
Describing the disease Person distribution

51. • Occupation may alter the habit pattern of employees (Sleep, alcohol,
smoking, etc)
• Workers in a particular occupation are exposed to certain types of
risk. Eg: Workers in coal mines are likely to suffer from silicosis
• V shaped abrasion of incisal edges of tailors due to repetitive use of
teeth as tool to place pin.
E) OCCUPATION
Describing the disease Person distribution

52. • Health and diseases are NOT equally distributed in social classes.
• Certain diseases show higher prevalence in upper class (Diabetes,
Coronary heart disease, hypertension) .
• Periodontitis is majorly seen in low socio-economic group.
F) SOCIAL CLASS
Describing the disease Person distribution

53. • Behavioral factors such as smoking, sedentary life, over-eating,
drug abuse, areca nut chewing lead to certain diseases (Coronary
heart disease, Cancer, smokers palate, OSMF etc)
• Factors like mass movement (Eg: Pilgrimages) may also lead to
transmission of infectious diseases.
G) BEHAVIOUR
Describing the disease Person distribution

54. • The effects of stress are seen based on the patient’s response.
(Susceptibility to disease, Exacerbation of symptoms, etc)
- oral ulcers, stress induced gingivitis.
I) MIGRATION
H) STRESS
Due to migration of people, there is also transmission of the
disease from one place to another.
Describing the disease Person distribution

55. STEP 4: MEASUREMENT OF DISEASE
• Types-
1) Cross sectional studies-
Prevalence can be obtained.
It is based on a single examination of a cross section of population at
one point in time.
• More useful for chronic diseases
• It provides very little information about natural history of disease or about
rate of occurrence of new cases.
‘Disease load’ in population
measurement of mortality
measurement of morbidity

56. 2) Longitudinal studies-
• Incidence can be obtained.
• The observations are repeated in the same population over a
prolonged period of time by means of follow up examination.
• Longitudinal is more useful, but it is time consuming.
• These studies are useful-
To study natural history of disease and its future outcome.
For identifying risk factors of the disease.
For finding out incidence rate.
MEASUREMENT OF DISEASE

57. STEP 5: COMPARING WITH KNOWN INDICES
• Making comparisons and asking questions
-Different populations or
-Subgroups of the same population
1.It is possible to arrive at clues to disease aetiology.
2. Identify groups which are at ‘high risk’ for the disease.
By making comparison between

58. STEP 6: FORMULATION OF A HYPOTHESIS
• A hypothesis is a supposition, arrived at from observation or
reflection.
• An epidemiologic hypothesis should specify-
The population-
characteristics of the people
to whom the hypothesis
applies
Specific cause
Expected outcome-the
disease
Dose response
relationship-The amount of
the cause needed to lead to
the stated
incidence of the effect.
Time response
relationship-Time period
between exposure to the
cause and
observation of the effect.

59. • Cigarette smoking causes lung cancer.
Smoking of 30-40 cigarettes per day causes lung cancer in
10 percent of smokers after 20 years exposure
STEP 6: FORMULATION OF A HYPOTHESIS

60. USES OF DESCRIPTIVE EPIDEMIOLOGY
It provides data regarding
the magnitude of the
disease load and types
of disease problems in
terms of morbidity and
mortality rates and ratios.
It provides clue to disease
etiology and help in the
formulation of an
etiological hypothesis.
Permit Evaluation of
Trends in Health and
Disease
It provides background
data for planning,
organizing and
evaluating preventive
health service.
Contribute to research by
describing variations in
disease occurrence by
time, place and person.
Identify Problems to Be
Studied by Analytic
Methods and Suggest
Areas That May Be
Fruitful for Investigation

63. TYPES OF DESCRIPTIVE EPIDEMIOLOGY
Case reports Case series
Ecological
studies
Cross sectional
studies
Longitudunal
studies

64. 1. CASE REPORTS
• Case report is the descriptive study of the individual in terms of a careful, detailed
report of a single patient.
• Lowest level of evidence and considered base of pyramid.
• Example:
A 28-year-old woman had been experiencing severe discoloration and surface defects on the
anterior teeth for more than 10 years. Clinical assessment revealed that the DF was severe and
had a significant impact on the esthetic appearance of the teeth. Considering the patient's
young age, more conservative treatment was proposed to improve the condition of her teeth
instead of the conventional restorative approaches. The proposed treatment was based on a
combined approach of enamel abrasion, tooth bleaching, and resin infiltration for managing the
enamel surface and periodontal scaling to prevent inflammation and improve the gingival status
before the formal treatment.
Shenoi P, Kandhari A, Gunwal M. Esthetic Enhancement of Discolored Teeth by Macroabrasion Microabrasion and its psychological
impact on patient -A case report. Indian Journal of multidisciplinary dentistry. 2011 Nov 1;2(1).

65. FEATURES OF THE CASE REPORT :
• It consists of a careful & detailed report (published in medical and
dental journals) by one or more clinicians of unusual medical/dental
condition.
It represents the 1st clue in the identification of a new disease.

66. ADVANTAGES AND DISADVANTAGES OF CASE
REPORT

67. 2. CASE SERIES
• It is the only study which depends on Routine Surveillance.
• It is characteristics of a number of patients with a given disease.
It is collection of individual case reports.
• Describe a set of patients having similar symptoms and
outcome.

68. • 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 of this circumstance showed high concentration of radon
gas. A hypothesis was formulated that lung cancer is related to
exposure to radon.
2. Case series

69. 2. Case series
Misch CE, Steigenga J, Barboza E, Misch‐Dietsh F, Cianciola LJ, Kazor C. Short dental implants
in posterior partial edentulism: a multicenter retrospective 6‐year case series study. Journal of
periodontology. 2006 Aug 1;77(8):1340-7.

70. ADVANTAGES AND DISADVANTAGES OF CASE
SERIES

72. 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.

73. THE LIMITATIONS OF THE CASE REPORT &
CASE SERIES:
• For the case report, the presence of any exposure may be coincidental
because it is based on a single experience .
• Lack of the comparison group in case series can either obscure the
relationship or suggest an association which is not actually exist.
• Both of them cannot be used to show the causal association i.e. can not be
used to test the hypothesis.
• Presence of risk factors may be purely coincidental and hence unreliable.

74. 3. 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.
• It describes outcomes in relation to age, time, utilization of services, or
exposures

75. RATIONALE FOR ECOLOGIC STUDIES
• Low cost and convenience
• Measurement limitations of individual level studies
• Design limitations of individual level studies
• Interest in ecologic effects
• Simplicity of analysis and presentation

76. TYPES OF ECOLOGIC STUDIES
1. Multiple group studies
2. Time trend studies
3. Mixed designs

77. 1.MULTIPLE GROUP STUDY
The relation between male obesity and income inequalities in 21 rich countries
Pickett K.E. et al. Wider income gaps, wider waistbands? An ecological
study of obesity and income inequality.
J Epidemiol Community Health. 2005 August; 59(8): 670–674
48

78. 2.TIME TREND STUDY
Åstrøm AN, Skaret E, Haugejorden O. Dental anxiety and dental attendance among 25-year-olds in Norway: time trends from 1997 to 2007. BMC oral
health. 2011 Dec;11(1):10.

79. ECOLOGICAL FALLACY
• Ecological fallacy is a bias results if inappropriate conclusions are
drawn on the basis of ecological data.
The bias occur because the association between variables at group level does not
necessarily represent the association that exist at the individual level
Cross-sectional ecological study relate frequency with which some characteristic and some outcome of
interest occur in same geographical area. These studies are useful for suggesting hypothesis, but cannot
be used to draw causal conclusions.
EX: Characteristic =sugary
snacks
outcome= dental caries
Here we cant draw causal conclusion, there is no information that
people who consumed sugary snacks are the same who developed
dental caries, it is unknown that exposure or the outcome came first.

80. ADVANTAGES OF ECOLOGICAL STUDY

81. DISADVANTAGES OF ECOLOGICAL STUDY

82. 4. CROSS-SECTIONAL STUDIES
• An “observational” design that surveys exposures and disease status
at a single point in time (a cross-section of the population)

83. • This type of investigation is defined as one “. . . that examines the relationship
between diseases (or other health-related characteristics) and other variables of
interest as they exist in a defined population at one particular time.
• A cross-sectional study is a type of prevalence study in which exposures and
distributions of disease are determined at the same time.
4. CROSS-SECTIONAL STUDIES

84. DESCRIPTIVE CROSS SECTIONAL STUDIES
• Information about single /multiple variables
• Estimate problem – Prevalence.
• Presence of disease, disability and symptoms of ill-health
• Dimensions of Positive health such as fitness
• Attributes related to health.
• Strength of association between disease & Risk factors
• Determinants of disease / conditions
• Predictors of disease / condition
ANALYTICAL CROSS SECTIONAL STUDIES

85. DESIGN OF CROSS-SECTIONAL STUDY

87. STEPS IN CONDUCTING CROSS-SECTIONAL STUDY
State the
criteria for
the disease
/ condition
clearly
Define co-
variables to
be
measured
Examine
ethical
issues
Identify
the
reference
population
inclusion
/
exclusion
criteria
Determine
minimum
number of
Sample
required
Select study
subjects
through
appropriate
sampling
procedure
Define
measureme
-nt
procedures
Carry out
data
collection
Interviews
and
Questionnair
-es
Clinical
records
and other
documents
Clinical
examina
tion
Report
Analyze
and
interpret
finding
Summarize
data

88. BIASES IN CROSS SECTIONAL STUDIES
• Choice of sampling frame
• Non – response
• Information bias
• Observer bias
• Prevalence Bias in Hospital Studies

89. SOME COMMON APPLICATIONS OF
CROSS-SECTIONAL STUDIES
• In Community Health Care
• In Clinical practice and Patient Care
• In Programme evaluation
• In acquiring new knowledge

90. EXAMPLE
Devaraj CG, Eswar P. Reasons for use and non-use of dental services among people visiting a dental college hospital in
India: A descriptive cross-sectional study. European journal of dentistry. 2012 Oct;6(4):422.

91. Advantages
Estimation of
prevalence rate
of disease or
any health
related
phenomena.
It is suitable for
chronic
diseases with
long
latency.
It leads to
formulation of
hypothesis.
Relatively short
duration
Quick & cheap,
compared to
case-control
& cohort
studies.
Limitations
Cannot
determine
whether
exposure
preceded
disease
It considers
prevalent
rather than
incident cases,
results will be
influenced by
survival factors
Not suitable for
rare diseases
(Compared with
the case control
study).
Can’t be used
in acute
diseases of
short duration.
4. CROSS-SECTIONAL STUDIES

92. 5. LONGITUDUNAL STUDY
IN A LONGITUDINAL STUDY DESIGN,
THE STUDY IS CONDUCTED AT TWO OR DIFFERENT POINTS OF TIME IN
THE LIFE TIME OF INDIVIDUALS UNDER STUDY IN CONTRAST TO THE
ONE TIME STUDY OF CROSS-SECTIONAL DESIGN.
Analysis involving some comparison of data between periods.
• Observations are repeated in the same population over a prolonged period of
time by follow up examination.
• Useful to study natural history of disease.
• Helps to find out incidence rate.
• Helps to identify risk factors of disease. Study is time consuming & costly.
• Dropouts during study period ( Attrition)

93. • OTHER NAMES :-
• INCIDENCE STUDY ( AS INCIDENCE CAN BE MEASURED
DIRECTLY),
• FOLLOW UP STUDY (AS CONTINUOUS FOLLOW UP IS
ESSENTIAL)
• PROSPECTIVE STUDY (AS THE DIRECTION OF THE STUDY IS
FORWARD-LOOKING.
5. LONGITUDUNAL STUDY

94. METHODOLOGY
DEFINING AND DESCRIBING THE POPULATION AFFECTED
(REFERENCE POPULATION AND STUDY POPULATIONS)
 DEFINING AND DESCRIBING THE DISEASE
OPERATIONAL CASE DEFINITIONS
TIME, PLACE AND PERSON TRENDS)
 FORMULATION OF HYPOTHESIS

95. POPULATION AT RISK
5. LONGITUDUNAL STUDY

96. REFERENCE POPULATION
• The population which is at risk and the health action has to be
initiated after the study is over is the reference population
or
• The population in which a particular disease or exposure has
occurred and is to be investigated
5. LONGITUDUNAL STUDY
Reference population is the one, which has to be get benefited after our
descriptive study.

97. STUDY POPULATION
This is the population on which the hypothesis is actually
studied and tested.
• It may be the entire reference population itself (if it is small and
feasible for study)
or
• A representative portion of it(sample).
5. LONGITUDUNAL STUDY

98. MAIN TYPES OF LONGITUDINAL STUDIES
• Prospective longitudinal studies or Panel studies
• Repeated cross-sectional studies or Trend
studies
• Retrospective longitudinal studies
• Simultaneous cross-sectional studies

99. PROSPECTIVE LONGITUDINAL STUDIES OR
PANEL STUDIES
• Panel studies are a particular design of longitudinal study in which the unit of
analysis is followed at specified intervals over a long period, often many
years. The key feature of panel studies is that they collect repeated
measures from the same sample at different points in time. (Laurie, 2013)
• Possibility to collect information about change at the micro level as it really
happens.
• Powerful non experimental method for examining development and
causality.

100. EXAMPLE

101. REPEATED CROSS-SECTIONAL STUDIES
OR TREND STUDIES
• Repeated cross-sectional data are created where a survey is
administered a new sample of interviewees at successive time points.
For an annual survey, this means that respondents in one year will be
different people to those in a prior year.

102. EXAMPLE :
Wennström A, Ahlqwist M, Stenman U, Björkelund C, Hakeberg M. Trends in tooth loss in relation to socio-economic
status among Swedish women, aged 38 and 50 years: repeated cross-sectional surveys 1968-2004. BMC oral health.
2013 Dec;13(1):63.

103. RETROSPECTIVE LONGITUDINAL STUDIES
• Retrospective longitudinal data are gathered during a single
investigation in which respondents are asked to think back and
answer questions about the past.
PROS CONS
• Time-saving
• Economic
Unreliable data from
participants

104. SIMULTANEOUS CROSS-SECTIONAL STUDIES
• Simultaneous cross-sectional studies are conducted with different age
groups sampled, only partially longitudinal, because it does not
involve the examination of change over time but rather across age
groups.
• Respondants’ age is the key sampling variable, while in ordinary
cross-sectional designs age is just another variable.

105. SURVEILLANCE STUDIES
The ongoing systematic collection, analysis and interpretation of health
data essential to the planning, implementation and evaluation of public
health practice, closely integrated with the timely dissemination of these
data to those who need to know.(CDC)
• Provide information to guide interventions
• Watchfulness over the community
WHO- surveillance and monitoring report on global tobacco epidemic 2019 offer help to quit tobacco use

106. USES OF SURVEILLANCE STUDIES:
• Estimating the magnitude of problem
• Determining the geographic distribution of illness
• Portraying the natural history of disease
• Detecting epidemics or defining a problem
• Generating hypothesis, stimulating research
• Evaluating control measures
• Monitoring changes in infectious agents
• Detecting changes in health practices
• Facilitating planning
SURVEILLANCE IS- “INFORMATION FOR
ACTION”

107. NATIONAL SURVEILLANCE PROGRAMME
FOR COMMUNICABLE DISEASE (NSPCD):
SURVEILLANCE STUDIES
The Government of India launched NSPCD
during 1997-1998. Main objective was to
strengthen the surveillance system of
communicable diseases and developing
capabilities at state and district level so
that disease outbreak can be detected early
in order to institute rapid response to avert
large number of morbidity and mortality.
INTEGRATED DISEASE SURVEILLANCE
PROGRAMME (IDSP): 2004
IDSP is a decentralized , state based
surveillance programme in the country.

108. A FREQUENT ERROR IN REPORTS OF DESCRIPTIVE
STUDIES
• Overstepping the data: studies without a comparison group allow no
inferences to be drawn about associations, causal or otherwise.
• Hypotheses about causation from descriptive studies are often tested
in rigorous analytical studies.

109. • Descriptive epidemiology classifies the occurrence of disease according to
the variables of person, place, and time allows epidemiologist to better
understand the nature and extent of health problem
• Descriptive epidemiologic studies aid in generating hypotheses that can be
explored by analytic epidemiologic studies.
• Some of the uses of descriptive epidemiology are to demonstrate which
health outcomes should be prioritized for the design of interventions

110. • Descriptive epidemiology through surveillance may identify sudden
outbreaks and fluctuations.
• It provides causal insights, it provide clues as to whether a physical,
chemical, biological or psychosocial factor is contributing to the
problem.

111. • K Park. Park’s textbook of preventive and social medicine.2019;25th ed:61-78
• Gordis L. Text book of Epidemiology. 5th ed. Elsevier
• saunders; 2013MacMohan,B.(1982)Grimes DA, Schulz KF. Descriptive studies: what
they can and cannot do. The Lancet. 2002 Jan 12;359(9301):145-9.
• Friis RH, Sellers TA. Epidemiology for Public Health Practice. 4th ed. Sudbury, MA:
Jones and Bartlett Publishers; 2009.
• MacMahon B, Pugh TF. Epidemiology Principles and Methods. Boston, MA: Little,
Brown; 1970.
• Merrill.M. Introduction to Epidemiology.2010;5th ed:83-153.

112. • Bonita R, Beaglehole R, Kjellstrom K. Basic Epidemiology.2006 Jan;2ND ed
• Bhalwar R. Text Book of Public Health and Community Medicine. 1st ed. Pune: Dept of Community Medicine,
AFMC. 2009. P. 144
• Halpern-Manners, A., & Warren, J. (2012). Panel Conditioning in Longitudinal Studies: Evidence From Labor
Force Items in the Current Population Survey. Demography, 49(4), 1499-1519.
• Laurie, H. Panel Studies. Oxford Bibliographies Online Datasets.2013
• Hudson K, Stockard J, Ramberg Z. The impact of socioeconomic status and race-ethnicity on dental health.
Sociological Perspectives. 2007 Mar;50(1):7-25.
• Senior P A, Bhopal R.Ethnicity as a variable in epidemiologic research.BMJ 1994;309:327-330.
• Menard S, editor. Handbook of longitudinal research: Design, measurement, and analysis. Elsevier; 2007 Oct
11.