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Epidemiology.ppt
1. “I KEEP SIX HONEST SERVING MEN; THEY
TOUGHT ME ALL I KNOW. THEIR NAMES ARE
WHAT, WHY, WHEN, HOW, WHERE AND WHO”
2. Introduction:
History:
• Epidemiology began with Adam and Eve
• The foundation of epidemiology was laid in the 19th century
• Epidemiological society in London in 1850s
• In the US, Winslow and Sedgwick both lectured in
epidemiology in 1920s.
• W.H Frost became the professor of epidemiology in US.
• Major Greenwood became the first professor of
epidemiology in London.
3. epidemic: epi=among; demons=people; logos=study
Branch of medical science which treats of epidemics:
Parkin,1873
The science of the mass phenomena of infectious disease
Frost, 1927
The study of disease, any disease, as a mass phenomena
Greenwood, 1934
The study of the distribution and determinants of disease
frequency in man
MacMohan,1960
4. Definition:
“The study of the distribution and determinants of health-
related states or events in specified populations and the
application of this study to the control of health
problems”.
John M. Last, 1988
5. Components:
1. Disease frequency
2. Distribution of disease –descriptive epidemiology
3. Determinants of disease-analytical epidemiology
Aims: according to the IEA, epidemiology has 3 main aims
1. To describe the distribution and magnitude of health and
disease problems in human populations.
2. To identify etiological factors in the pathogenesis and
3. To provide the data essential to the planning,
implementation and evaluation of the services for the
prevention, control and treatment of disease and to the
setting up of priorities among those services.
6. The ultimate aim of epidemiology is to lead to effective
action
a. to eliminate or reduce the health problems or its
consequences
b. to promote the health and well-being of society as a
whole
7. Epidemiological approach
1. Asking questions
2. Making comparison
1.Asking questions: asking questions and getting answers that
lead to further questions
a. Related to health events
• What is the event? (the problem)
• What is its magnitude?
• Where did it happen?
• Who are affected?
• Why did it happen?
8. b. Related to health action
What can be done to reduce this problem and its consequences ?
How can it be prevented in the future?
What action should be taken by the community? By the health
services? By other sectors? Where and for whom these activities be
carried out?
What resources are required? How are the activities to be organized?
What difficulties may arise, how might they be overcome?
2. Making comparisons
9. Measurements in Epidemiology
a. Measurement of mortality
b. Measurement of morbidity
c. Measurement of disability
d. Measurement of natality
e. Measurement of the presence, absence, or distribution
of the characteristic or attributes of the disease
10. f. Measurements of medical needs, health care facilities,
utilization of health services and other health- related
events
g. Measurements of the presence, absence or distribution of
the environmental and other factors suspected of causing
the disease
h. Measurements of demographic variables
Requirements of measurements are:
• Reliability * Validity
• Accuracy * Sensitivity and
• Specificity
11. Tools of measurements
1. Rates: a rate measures the occurrence of some particular
event
number of deaths in one year
Death rate= ------------------------------------x1000
mid- year population
Elements of rates:
numerator, denominator, time specification and multiplier
Categories of rates:
• Crude rates/unstandardized-actual observed rates
• Specific rates-actual observed rates due to specific causes,
groups, or time
• Standardized rates
12. 2. Ratio: Ratio expresses a relation in size between two
random quantities.
x
x:y or ---- eg. Sex ration
y
Proportion: a proportion is a ratio which indicates the
relation in magnitude of a part of the whole
No of children with scabies at a certain time
Eg. ----------------------------------------------------- x 100
Total no of children in the village at the same time
13. Measurement of mortality:
1. Death certificate
2. Uses of mortality data: mortality data
a. Explains trends and differentials in overall mortality
b. Indicates priority for health action and the allocation of
resources
c. Employed in designing intervention programs
d. Helps in monitoring of public health problems and
programs
e. Gives clue for epidemiological research
3.Limitations of mortality data:
a. Incomplete reporting of deaths
b. Lack of accuracy
14. c. Lack of uniformity
d. Choosing a single cause of death
e. Changing
f. Disease with low fatality
Mortality rates and ratios
1.Crude death rate
The no of deaths (from all causes) per 1000 estimated
mid-year population in one year, in a given place
No of death during the year
Crude death rate= ------------------------------------x1,000
mid year population
15. 2. Specific death rates:
specific death rates may be
a. Cause or disease specific e.g; TB, Cancer
b. Related to specific groups e.g; age specific, sex-specific
No of deaths from TB during a calendar year
specific death rate due to TB= ------------------------------------------x1,000
mid-year population
No of deaths in a particular population
Age specific death rate=------------------------------------------------x 1,000
Mid year population of that age group
16. No of deaths of person aged 15-20 during a
calendar year
Specific death rate in age group= ------------------------------------x 1,000
15-20 years Mid year population of person aged 15-20
Male deaths
Sex specific death rate=---------------------x 1, 000
Mid year population of males
No of deaths among males during a calendar year
Specific death rate for males= -----------------------------------------x1,000
mid-year population of males
17. Female deaths at specific aged 15-20 years
Age-Sex specific death rate=-----------------------------------------x 1,000
Female population aged 15-20 years
Deaths in January x 12
Death rate for January= -----------------------x 1,000
Mid- year population
Deaths in the week x 52
Weekly death rate = ---------------------------- x 1,000
Mid- year population
18. 3. Case fatality rate (Ratio)
Total number of deaths due to a particular disease
= ---------------------------------------------------------x100
Total number of cases due to the same disease
4. Proportional mortality rate (Ratio)
a. Proportional mortality from a specific disease
No of deaths from the specific disease in a year
= ---------------------------------------------------------x100
Total deaths from all causes in that year
b. Under -5 proportionate mortality rate
No of deaths under 5 years of age in the given year
= --------------------------------------------------------------x100
Total no of deaths during the same period
19. 5. Proportional mortality rate for aged 50 years and above
No of deaths of persons aged 50 years and above
= -------------------------------------------------------------x 100
Total deaths of all age groups in that year
d. Survival rate:
Total no patients alive after 5 years
= ------------------------------------------x100
Total no of patients diagnosed or treated
6. Infant mortality rate:
Total no of infants deaths in a year
= ------------------------------------------ x1000
Total no. of live births in that year
20. Under 5 mortality rate:
No of deaths under 5 years of age in year
= ------------------------------------------ x1000
Total no. of live births in that year
Maternal mortality ratio:
Total no. of maternal deaths in a year
= ------------------------------------------ x100000
Total no. of live births in that year
21. Years of potential life lost: YPLL is based on the
years of life lost through premature death. It is defined
as one that occur before the age to which a dying
person could have expected to survive.
A 30 years old who dies in a road accident could
theoretically have lived to an average life expectancy of
75 years of age; thus 45 years of life are lost.
22. Measurement of morbidity
Morbidity is defined as “any departure, subjective, or
objective, from a state of physiological well-being”
Morbidity=sickness, illness, disability
Morbidity could be measured in terms of 3 units
a. persons who were ill
b. the illnesses (spells of illness) that these persons
experienced and
c. the duration of these illnesses
Morbidity rates:
Disease frequency=incidence and prevalence
Duration of illness=average duration/case or the disability rate
Severity of illness=case fatality rate
23. Value of morbidity data
a. They describe the extent and nature of the disease load in
the community and thus assist in the establishment of
priorities
b. They provide more comprehensive and more accurate and
clinically relevant information on patient characteristics
and therefore essential for basic research
c. They serve as starting point for etiological studies, and
thus play a crucial role in disease prevention
d. They are needed for monitoring and evaluation of disease
control activities
24. Incidence: “No of new cases occurring in a defined
population during a specified period of time”
No of new cases of specific disease during a
given time period
Incidence= -----------------------------------------------------------------x1,000
population at risk during that time
eg., New cases of an illness 500
population at risk 30,000
Incidence rate= 500/30,000x1000= 16.7 per 1000 per year
Incidence rate refers
* only to new cases
• during a given period
• In a specified population
25. No of spells of sickness starting in a defined period
Incidence rate=--------------------------------------------------------------x1000
(spells) Mean no of persons exposed to risk in that period
No of new cases of a specified disease during a specified time
interval
Attack rate:-------------------------------------------------------------------x100
Total population at risk during the same interval
Attack rate is used during epidemic to know the extent of the epidemic
26. Secondary attack
No of exposed persons developing the disease within the
range of the incubation period following exposure to a primary
Case.
No of new cases of a specified disease during a specified time
interval
Secondary Attack rate=
No. of exposed persons developing the disease within
the range of the incubation period
--------------------------------------------------------------------x100
Total no. of exposed/susceptible contacts
27. Uses of incidence
a. To control disease
b. For research into etiology and pathogenesis, distribution of
diseases and efficacy of preventive and therapeutic
measures.
28. Prevalence
“All current cases (new and old) existing at a given point time,
or over a period of time in a given population”
Types of prevalence
a. Point prevalence
b. Period prevalence
Point prevalence: the no. of current cases of a disease at one
point in time in relation to a defined population
No of all current cases of a specified disease existing at a
given point in time
--------------------------------------------------------------------------------------------x100
Estimated population at the same point in time
29. Period prevalence:
Frequency of all current cases existing during a defined
period of time
No of all existing cases of a specified disease during a
given period of time interval
--------------------------------------------------------------------------x100
estimated mid interval population at risk
Relationship between prevalence and incidence:
Prevalence = incidence x duration (P=I x D)
Longer the duration of the illness, greater its prevalence
30. Uses of prevalence:
1. Helps to estimate the magnitude of health problems and
identify potential high risk population
2. Useful for administrative and planning purposes e.g: hospital
beds, manpower needs, rehabilitation facilities
31. Other morbidity indicators
Notification rates
Attendance rates at O.P.D. , health centers
Admission , readmission and discharge rates
Duration of stay in hospital
32. Disability rates
Event type indicator:
I. Number of days of restricted activity.
II. Bed disability days
III. Work-loss days within a specified period.
Person type indicator:
I. Limitation of mobility
II. Limitation of activity
33. HALE(Health adjusted life expectancy)
Qualified adjusted life year(QALY)
Disability-free life expectancy
Disability adjusted life years(DALY )
34. Nutrition status indicators
Anthropometric measurements of preschool children.
Height of children at school entry
Prevalence of low birth weight
35. Health care delivery indicators
Doctor-population ratio
Doctor-nurse ratio
Population –bed ratio
Population per health/ subcentre
Population per trained birth attendant
36. Other indicators
Utilization rates
Indicators of social and mental health
Environmental indicators
Socio economic indicators
Health policy indicators
Indicators of quality of life
Social indicators
Basic need indicators
37. Association and causation
Association: Concurrence of two variables more often
than would be expected by chance.
Events are said to be associated when they occur more
frequently together than one would expect by chance.
38. Correlation
Correlation indicates the degree of association
between two characteristics.
The correlation coefficient ranges from -1.0 to +1.0.
A correlation coefficient of 1.0 mean that the two
variables exhibits a perfect linear relationship.
But correlation cannot be used to invoke causation.
Correlation does not measure the risk.
Causation implies correlation, but correlation does not
implies causation.
39. Types of association
1. Spurious association
2. Indirect association
3. Direct association
a. One to one causal association
b. Multifactorial causation
41. Indirect association
Many associations which at first appeared to be causal
have been found on further study to be due to indirect
association.
The indirect association between a characteristic (or
variable) of interest is a statistical and a disease due to
the presence of another factor, known or unknown,
that is common to both the characteristic and the
disease.
47. Hill criteria/Surgeon general
criteria
Temporal association
Strength of association
Specificity of association
Consistency of association
Biological plausibility
Coherence of the association
48. Temporal association
Most important Criteria
Best established with Cohort study
Cause should proceed effect
E.g.: Smoking should lead to lung cancer.
49. Specificity of association
Most difficult to be establish /least important
Only one cause should lead to one disease.
50. Strength of association
It is based on answer to two questions:
Relative risk-is it large?
Is there a dose response , duration-response
relationship?
Larger the relative risk, the greater the likelihood of a
causal relationships.
The likelihood of a casual relationship is strengthened
if there is a biological gradient or dose-response
relationship.
51.
52. Consistency of association
Results should be replicable in different settings.
The association is consistent if the results are
replicated when studied in different settings and by
different methods.
53. Biological plausibility
Causal association is supported if there is biological
credibility to the association, that is the association
agrees with current understanding of the response of
cell, tissues, organs and system to stimuli.
54. Coherence of the association
A final criterion for the appraisal of causal significance
of an association is its coherence with known facts that
are thought to be relevant.
E.g. The historical evidence of rising consumption of
tobacco in the form of cigarette and the rising
incidence of lung cancer are coherent.
55. Measures of association
Measures of association compares measures of disease
occurrence in 2 different groups, the exposed group
and the unexposed groups.
Comparison can be made by:
Division (ratio effect measures)
Subtraction (difference effect measure)
56. Types of measures of
association
Relative risk
Odd ratio
Attributable risk
57. Relative risk
The estimation of risk associated with exposure is
obtained by an index known as Relative risk or relative
ratio.
Relative risk/ratio is defied as the ratio between the
incidence of diseases among exposed person and
incidence among non-exposed.
58. Relative risk/Ratio
Relative risk=
Incidence among exposed
--------------------------------
Incidence among non exposed
e.g.
59. Practice question
In a general population of 100 individual were smoker
and out of them 80 developed the diseases condition.
On the other hand out of 100 individuals who does not
smoke out of them 30 individuals develop lung cancer.
Find out the relative risk.
60. Odd ratio(Cross product ratio)
Odd ratio is a measure of the strength of the
association between risk factor and outcome.
Odd ratio is closely related to relative risk.
61. The derivation of odd ratio is based on three
assumptions:
The disease being investigated must be relatively
rare. In fact, the majority of the chronic diseases
have a low incidence in the general population.
The cases must be representative of those with the
disease
The control must be representative of those without
the diseases.
62. The odd ratio is the cross product of the entire table:
Disease
Yes No
Exposed a b
Not Exposed c d
Odd ratio= ad/bc
63. Practice question
In a general population of 100 individual were smoker
and out of them 80 developed the diseases condition,
where as 20 does not develop lung cancer.
On the other hand out of 100 individuals who does not
smoke out of them 30 individuals develop lung cancer
and 70 were safe.
Find out the odds ratio.
64. Attributable risk (AR)/Risk
Difference
Attributable risk (AR) is the difference in incidence rates of
disease (or death) between an exposed group and non-
exposed group.
incidence of disease rate among exposed
-incidence rate among non exposed
= -------------------------------------------x100
incidence rate among exposed
10-1
--------x100 =90 per cent
10
65. Epidemiological methods
Observational studies Experimental or intervention studies
a. Descriptive studies Randomized controlled trials or clinical studies
b. Analytical studies Field trials or community intervention studies
i). Ecological or cor-relational Community trials
ii). Cross-sectional or prevalence
iii). Case control or case reference
iv). Cohort or follow up
66. Descriptive Epidemiology:
• It is the first phase of an epidemiological investigation
• It is concerned with observing the distribution of disease
or health related characteristics in human population
• Identifies the characteristics with which the disease in
question seems to be associated
Descriptive studies basically ask the following questions
a. When is the disease occurring?-time distribution
a. Where it is occurring?-place distribution
a. Who is getting the disease?-person distribution
67. Procedures in descriptive epidemiology
1. Defining the population being studied: defined population
• in terms of total number, and its composition such as age,
sex, occupation, cultural characters etc…
• can be the whole population or representative sample
• can also be a specific group like age group, sex group etc
• needs to be large enough
• should be stable and should not be overtly different from
other population
Defined population provides denominator for calculating rates
68. 2. Defining the disease under study
Operational definition: a definition by which the disease or
condition can be identified and measured in the defined
population with degree of accuracy
3. Describing the disease
Describe the occurrence and distribution of disease by time,
place and person
A. Time distribution
• pattern of disease described by year, month, week, day of the
week, hour of onset etc.
• Whether disease is seasonal in occurrence, shows periodic
or , follows consistent time trend.
69. Time trends or fluctuations
a. Short term-fluctuations b. Periodic fluctuations
c. Long-term fluctuations
Short term fluctuations: the short term fluctuation in the
occurrence of a disease is an epidemic
Types of epidemic
i Common source epidemics
• Single source or point source epidemics
• Continuous or multiple exposure epidemics
ii. Propagated epidemics
person to person
arthropod vector
animal reservoir
iii. Slow (modern) epidemics
70. Common- source
single or point exposure epidemics
Epidemic curve
• the epidemic curve rises and falls rapidly with no secondary
waves
• the epidemic tends to be explosive, there is clustering of
cases within a narrow interval of time
• all cases develop within one incubation period of disease
eg; food poisoning, Bhopal gas tragedy
71. Common source, continuous or repeated exposure
• Exposure from the same source prolonged-continuous,
repeated or intermittent
Propagated epidemics:
* Epidemic usually shows a gradual rise and tails off over over
a much longer period of time
• Speed of spread depends upon herd immunity, opportunities
for contact and secondary attack rate
• Transmission continues until the no of susceptible is
depleted or susceptible individuals are no longer exposed to
infected person
72. Periodic fluctuations
i) Seasonal trend
ii) Cyclic trend
Long-term or secular trends
B. Place distribution
a. International variations
b. National variations
c. Rural-urban differences
d. Local distributions
C. Person distribution
a. Age e. Occupation i. Migration
b. Sex f. Social class
c. Ethnicity g. Behavior
d. Marital status h. Stress
73. 4. Measurement of disease
5. Comparing with known indices
6. Formulation of a hypothesis
Uses of descriptive epidemiology
a. Provides data regarding the magnitude of the disease load
and type of disease problems
b. Provides clue to disease etiology and helps in formulation
of etiological hypothesis
c. Provide back ground data for planning, organizing and
evaluating preventive and curative services
d. Contributes to research by describing variations in disease
occurrence by time, place and person
74. Analytical epidemiology
Analytical studies determines
• Whether or not a statistical association exits between a disease and a
suspected factor and
• If one exists, the strength of the association
Types:
a. Case control study
b. Cohort study
a. Case control study or Retrospective study:
It is the first approach to test causal hypothesis
The three distinct features of case control study
• Both exposure and outcome (disease) have occurred before the start
of the study
• The study proceeds backwards from the effect to cause and
• It uses a control or comparison group to support or refute an
inference
75. Case control studies are basically comparison studies
Cases and controls must be comparable with respect to known
“confounding factors” such as age, sex, occupation, social status etc.
Design of case control study (2x2 contingency table)
Risk factor Cases Control
Present a b
Absent c d
a+c b+d
76. The basic steps
1. Selection of cases and control
A. Selection of case
a. Definition of a case i. Diagnostic criteria
ii. Eligibility criteria
b. Sources of cases i. Hospitals
ii. General population
B. Selection of controls
a. Sources of control i. Hospital controls
ii. Relatives
iii.Neighbourhood controls
2. Matching
It is process by which we select controls in such a way that they are
similar to cases with regard to certain pertinent selected variables
which are known to influence the outcome of disease.
“Group matching and Pair matching”
77. 3. Measurement of exposure
4. Analysis
a. Exposure rates among cases and controls to suspected factor
b. Estimation of disease risk associated with exposure (odds ratio).
a. Exposure rates:
Total 35 82
(a+c) (b+d)
i. cases =a/ (a+c)=33/35=94.2 percent
ii. controls-=b/ (b+d)==55/82=67.0 percent
P < 0.001
Cases controls
Smokers
(<5cig/day)
33
(a)
55
(b)
Non
smokers
2
(c)
27
(d)
78. b. Estimation of risk
Incidence among exposed
Relative risk= -------------------------------
Incidence among non exposed
a c
= ------ + -------
a+b c+d
Odds ratio (cross product ratio):
Diseases
----------------------------------
yes no
exposed a b
Non exposed c d
odds ratio=ad/bc
33x27
= -----------= 8.1
55x2
79. Derivation of odds ratio is based on 3 assumptions
The disease being investigated must be relatively rare
The cases must be representative of those with the disease and
The controls must be representative of those without the disease
Bias in case control study
a. Bias due to confounding
b. Memory or recall bias
c. Selection bias
d. Berkesonian bias
e. Interviewer’s bias
80. Advantages:
1. Relatively ease to carry out
2. Rapid and inexpensive (compared with cohort studies)
3. Require comparatively few subjects
4. Particularly suitable to investigate rare diseases or diseases about
which little is known
5. No risk to subjects
6. Allows the study of several different etiological factors
7. Risk factors can be identified. Rational prevention and control
programs can be established
8. No attribution problems, because case control studies do not require
follow-up of individuals into the future
9. Ethical problems minimal
81. Disadvantages:
1. Problems of bias relies on memory or past records, the
accuracy of which may be uncertain; validation of
information obtained is difficult or sometimes impossible
2. Selection of an appropriate control group may be difficult
3. We can not measure incidence, and can only estimate the
relative risk
4. Do not distinguish between causes and associated factors
5. Not suited to the evaluation of therapy or prophylaxis
therapy
6. Another major concern is the representativeness of cases
and controls
82. Cohort study: Prospective study, longitudinal study, incidence study,
forward looking study
Features of cohort study:
a. The cohorts are identified prior to the appearance of the disease
under investigation
b. The study groups are observed over a period of time to determine
the frequency of disease among them
c. The study proceeds forward from cause to effect
Concept of cohort
As a group of people who share a common characteristics or experience
within a defined time period. Eg., age, occupation etc…
Birth cohort, marriage cohort, exposure cohort etc….
Comparison group
83. Indications for cohort study
a. When there is good evidence of an association between exposure and
disease as derived from clinical observations and supported by
descriptive and case control studies
b. When exposure is rare, but the incidence of disease high among
exposed, exposure to X-rays etc….
c. When attribution of study population can be minimized, eg., follow-
up is easy, cohort is stable, co-operative and easily and
d. When ample funds are available
84. Types of cohort studies
1. Prospective cohort studies ( or “current” cohort study)
2. Retrospective cohort studies ( or “historical study)
3. Combination of retrospective and prospective cohort studies
Elements of a cohort study
1. Selection of study subjects
a. General population
b. Special groups i) Select groups
ii) Exposure groups
2. Obtaining data on exposure
a. Cohort members: personal interviews or mailed questionnaires
b. Review of records
c. Medical examination or special tests
d. Environmental surveys
According to whether or not they have been exposed to the suspected
85. 3. Selection of comparison groups
a. Internal comparisons
b. External comparisons
c. Comparison with general population rates
4. Follow-up: the methods should be devised depending upon the
outcome to be determined, to obtain data for assessing the outcome.
Procedures required comprise:
a) Periodic medical examination of each member of the cohort
b) Reviewing physician and hospital records
c) Routine surveillance of death records
d) Mailed questionnaires, telephone calls, periodic home visits
5. Analysis: the data are analyzed in terms of:
a. Incidence rates of outcome among exposed non exposed
b. Estimation of risk
86. Incidence rates:
a). among smokers = 70/7000 = 10 per 1000
b). among non-smokers = 3/3000 = 1 per 1000
Statistical significance: P < 0.001
b). Estimation of risk: i. Relative risk (Risk ratio)
ii. Attributable risk
RR is the ratio of the incidence of the disease among exposed and the
incidence among non exposed cohorts
incidence of disease (or death) among exposed
RR --------------------------------------------------------------
incidence of disease (or death) among non-exposed
Smoking Developed
lung
cancer
Not
developed
lung cancer
Total
Yes 70 6930 7000
No 3 2997 3000
87. 10
RR of lung cancer = ------ =10
1
Attributable risk (AR) is the difference in incidence rates of disease (or
death) between an exposed group and non-exposed group.
incidence of disease rate among exposed
minus-incidence rate among non exposed
= ------------------------------------------------------------------x100
incidence rate among exposed
10-1
--------x100 =90 per cent
10
88. Advantages:
• Incidence rate can be calculated
• Several possible outcome related to exposure can be studies
simultaneously
• Provides direct estimate of relative risk
• Dose response ratios can be calculated
• Certain forms of bias can be minimized
Disadvantages
• Cohort studies involve a large number of people
• It takes a long term to complete the study and obtain results
• Certain administrative problems such as loss of experienced staff, loss
of funding and extensive record keeping are inevitable
• It is not unusual to lose a substantial proportion of the original cohort
• Selection of comparison groups is a limiting intake
• Expensive
• Ethical problems
• There may be changes in the standard method or diagnostic criteria
89. Experimental Epidemiology: (Randomized controlled trials )
Aims:
a. To provide “scientific proof” of etiological (or risk) factors which may
permit the modification or control of those disease and
b. To provide a method of measuring the effectiveness and efficiency of
health services for the prevention, control and treatment of disease
Animal studies: application of animal studies
a. Experimental reproduction of human disease in animals to confirm
etiological hypotheses and to study pathogenic phenomena
b. Testing the efficacy of preventive and therapeutic measures and
c. Completing the natural history of diesase
90. Advantages of animal studies
• Animals can be bred and manipulated easily
• Animals multiply rapidly and enable to carry out certain experiments
(genetic experiments)
Disadvantages:
• Not all human diseases can be reproduced in humans
• All the conclusions derived from animals studies can not be applicable
in humans
Human experiments:
• To investigate disease etiology
• To evaluate the preventive and therapeutic measures
• Investigation of disease that cannot be produced in animals
91. Types of experimental studies
A. Randomized controlled trials
B. Non -Randomized or “non-experimental” trials
Randomized controlled trials
Steps in RCT
1. Drawing up a protocol
2. Selecting reference and experimental populations
a. Reference or target population
b. Experimental or study population
• Obtain informed consent
• Eligibility criteria
3. Randomization
4. Manipulation
5. Follow-up
6. Assessment: i. Positive result ii. Negative result
92. Bias
• Subject variation
• Observer bias
• Bias in evaluation
Blinding
• Single blind trial
• Double blind trial
• Triple blind trial
Study designs
* Concurrent parallel study design
*Cross over type of design
Types of RCT
1. Clinical trials
2. Preventive trials
3. Risk factor trials
