Epidemiology.pptx

MEASUREMENT OF
OUTCOMES IN
PHARMACOEPIDEMIOLOGY

Basic measurements in
epidemiology
a) Measurements of mortality.
b) Measurements of morbidity.
c) Measurements of disability.
d) Measurements of the presence, absence or
distribution of the characteristics or attributes of the
disease.
e) Measurements of the presence, absence or
distribution of the environmental and other factors
suspected of causing the disease.
f) Measurements of the medical needs, health care
facilities, utilization of health services and other
factors suspected of causing the disease.
g) Measurements of demographic variables.

Outcome Measures
 The World Health Organization International
Classification of Function describes three separate
levels of disablement impairment, activity limitation
and participation restriction, all of which present
separate measurement issues. Activity limitation is the
focus of a wide range of outcome measures that differ
greatly in terms of the specific activities included.
 These measures also employ a variety of
measurement dimensions, including amount of
assistance, degree of difficulty, frequency, time, and
quality. In addition to disability measures, the broad
concept of health-related quality of life (HRQOL) has
become an outcome of interest.

Outcome Measures
Outcomes of Disease - The 5 Ds
1. Death : A bad out come
2. Disease : A set of symptoms, physical signs, and laboratory abnormalities
3. Discomfort : Symptoms such as pain, nausea, and itching
4. Disability : Impaired ability to go about usual activities at home, work, or
recreation
5. Dissatisfaction : Emotional reaction to disease and its care, such as sadness
or anger
The outcome of a study is a broad term for any defined disease, state of
health, or
pharmacotherapy. In some studies, there may be multiple outcomes. The
exposures and outcomes of interest are specific to study hypotheses and
should always be clearly defined before the study starts. We measure
health outcomes to help us make decisions about managing our patients.
Outcome measures help us predict which patients will benefit most from a
particular
intervention and to document whether the patient improves after the
intervention is provided. There is a wide range of important health

Outcome Measures
The term risk factor is often used to describe an exposure variable. The exposure of
interest in one study may be the outcome in another. Ex: Smoking is clearly the
exposure of interest in a study that examines whether smokers are more likely to
develop lung cancer than non-smokers. It would be the outcome in a study
examining the effectiveness of an antismoking intervention programme in reducing
the frequency of smoking in a certain population.
Need for Outcome Studies: The health care costs are escalating continuously. It
generates more and more interest in the area of cost containment programs without
compromising quality of services. With the popularisation of health insurance in the
developed countries, managed care organisations (MCOs) and large employer
groups started using outcome measurement tools to identify, measure and evaluate
the results of care. Conduct of outcome studies help to empower the health care
organisations to determine which treatment or therapy program gives better clinical,
humanistic and cost effective outcomes for their members and also to validate the
outcome of care. Clinical researchers, clinicians, epidemiologists, statisticians and
economists are becoming more actively involved in outcome research and
measurement.
Classification of Outcomes: Although outcome measures are continuously
evolving, they give valid information to clinicians for choosing best therapeutic plan
for specific conditions and situations. In the past clinical measures were focussed
on mortality and morbidity. Today clinical effects go beyond the traditional markers
of morbidity and mortality and include a number of other aspects like economic and

Classification of Outcomes
Clinical results: Improvement in the condition,
deterioration/ worsening of condition or no change in
the condition.
Functional Status: Factors like ability to work, level of
functioning, whether supervision needed or not.
Patient satisfaction: Various aspects of care like
delivery care, effect on daily activities or life
satisfaction.
Economic measures: Here the factors like cost of
financial burden and the benefits obtained are noted.
Humanistic measures: Various aspects of quality of

Tools of measurement
 Rates
 Ratios
 Proportions

Tools of measurements
Rate: A rate measures the occurrence of some
particular event ( development of disease or
the occurrence of death) in a population during
given time period.
Rate = no of deaths in one year * 1000
mid year population
Consists : Numerator, denominator, time factor
and multiplier
e.g.. CBR, CDR.

The various categories of rates
are:
 1) Crude rates: These are the actual observed
rates such as the birth and death rates. Crude
rates are also known as unstandardized rates.
 2) Specific rates: These are the actual observed
rates due to specific causes (e.g.. tuberculosis); or
occurring in specific groups (e.g., age-sex groups)
or during specific time periods (e.g., annual,
monthly or weekly rates).
 3) Standardized rates: These are obtained by
direct or indirect method of standardization or
adjustment, e.g.,age and sex standardized rates.

Ratio: It expresses a relation between two
random quantities.
X:Y or X
Y
E.g.. Sex ratio, child-woman ratio, doctor-
population ratio.

Proportion: A proportion is a ratio which
indicates the relation in magnitude of a part of
the whole.
The numerator is always included in
denominator.
The proportion is usually expressed in
percentage.

Measurements of mortality
Crude death rates: “ the number of deaths ( from all causes) per
1000 estimated mid year population in one year, in a given
place”.
CDR = No. of deaths during the year * 1000
Mid year population.
Limitation of CDR is exposed when we compare age-specific
death rates b/w two populations.
Major disadvantage of CDR is:
They lack comparability for communities populations that differ by
age, sex, race etc

Specific death rate:
SDR= Death due to specific cause * 1000
Mid-yr population
Useful when planning to find out etiology
May be a) cause or disease specific e.g. TB, Cancer etc.
b) Related to specific groups- age specific, sex specific etc.
Advantages:
It helps us to identify particular groups or groups at risk for preventive
action.
They permit comparisions b/w different causes with in same
population.
Disadvantages: mainly used in developed countries where they have
civil registration system.

Case fatality rate:
= Total no. of deaths due to particular disease *
100
Total no. of cases due to the same disease
 It represents the killing power of a disease
 Ratio of death to cases
 Time interval is not specified
 Useful in acute infectious diseases e.g.
cholera, measles
 It is closely related to virulence of organism.

=“No of deaths due to a particular cause or in a
specific age group per 100 or 1000 deaths”.
a) Proportional mortality of a specific disease
= no. of deaths from the specific disease in a year *
100
total deaths from all causes in that year
b) Under 5 proportionate mortality rate
= no of deaths under 5 yrs of age in a given year *
100
total no of deaths during the same period
Proportional mortality rate (ratio)

 Proportional mortality rates are usually used
for broad disease group and for specific
disease of major public health importance e.g.,
cancer, CHD
 It is used when population data is not available
 Depends upon only two variables, which differ.
So it cannot be used for comparison b/w
population groups or different time periods.

Survival rate:
= Total no. of patients alive over a period *100
Total no. of patients diagnosed or treated
 It is the population of survivors in a group
studied and followed over a period e.g. for 5 yr
period
 Helps in describing prognosis in certain
disease
 Can be used as a yard stick for the
assessment of standards of therapy.

 If SMR is greater than 100, then the occupation
would appear to carry a greater mortality risk than
that of the whole population.
 If SMR is less than 100, then the occupation
risks of mortality would seem to be
proporiionately less than ihat for the whole
population.
 The SMR is better than direct standarization
because it permits adjustment for age and
other factors.

Measurements of morbidity
Morbidity is defined as “ any departure,
subjective or objective, from a state of
physiological well-being”.
Morbidity rates/ratios measured by
1) Frequency of disease: incidence and
prevalence.
2) Duration of illness: days, months and years
3) Severity of illness: case fatality rates.

Importance of morbidity data
 To know extent and nature of the disease load
in community and help in forming priorities.
 Provide more comprehensive and accurate
and clinically relevant information on patient
characterisitcs- essential for basic research.
 Starting point of etiological studies and plays
crucial role in disease population.
 Needed for monitoring and evaluation of
disease control activities.

Incidence
 “ No of new cases occuring in a defined population during a
specified period of time”.
= no of new cases of specific disease during a given time period
* 1000
population at risk during that period
It refers
1. Only to new cases
2. During a given period
3. In a specified population or population at risk
4. New spells or episodes of disease in a given population in
the given duration
5. Usually restricted to acute conditions

Special incidence rates
 Attack rate (case rate), Secondary attack rate,
Hospital admission rate, etc.
 a. Attack rate : An attack rate is an incidence rate
(usually expressed as a per cent), used only when
the population is exposed to risk for a limited
period of time such as during an epidemic.
 It reflects the extent of the epidemic.
 Attack rate is given by the formula:
 Number of new cases of a specified disease
during a specified time interval
x 100
Total population at risk during the same interval

Uses of incidence rate
 To control disease, and
 For research into aetiology and pathogenesis,
distribution of diseases, and efficacy of
preventive and therapeutic measures .

Cumulative incidence
 Cumulative incidence is a simpler measure of the
occurrence of a disease or health status.
 Unlike incidence, it measures the denominator
only at the beginning of a study.
 The cumulative incidence can be calculated as
follows:
 CI= Number of people who get a disease during a
specified period X
1000
Number of people free of the disease in the
population at risk at the beginning of the

 In a statistical sense, the cumulative incidence is
the probability that individuals in the population
get the disease during the specified period.
 The period can be of any length but is usually
several years, or even the whole lifetime.
 The cumulative incidence rate therefore is similar
to the “risk of death” concept used in life-table
calculations.
 The simplicity of cumulative incidence rates
makes them useful when communicating health
information to the general public.

PREVALENCE
 The term "disease prevalence" refers
specifically to all current cases (old and new)
existing at a given point in time, or over a
period of time in a given population.
 Prevalence is a ratio but expressed as a rate
 Two types
 Point prevalence
 Period prevalence

 Point prevalence:
No of all current cases (old + new) at one point of
time in a defined population
= no of all current cases(old+new) of a specified
disease existing at a given point in time
Estimated population at the same point in time
 Period prevalence
= no of existing cases (old+ new) of a specified
disease during a given period of time interval
* 100
estimated mid- interval population at risk

Prevalence = Incidence x duration.
(if population is stable and incidence and
duration are unchanging)
Incidence = P/D
Duration= P/I
Longer the duration: greater is the prevalence
rate
e.g. TB
Acute disease: short duration and rapid
recovery. So prevalence is less than incidence.
Relationship between prevalence and incidence

Uses of prevalence
 Estimating magnitude of health/ disease
problems in the community
 Identify potential risk populations
 Useful for adminstrative and planning
purposes

Units of drug dispensed
 Units of drugs represent measures like number of
capsules or tablets or doses of vaccines. Compared to
number of prescriptions, it is easy to find the number
of drug dispensed.
 This type of studies help to analyze the drug use
trends in various countries or various states or
territories of a country. It too has limitations like units
of drugs dispensed need not always reflect the actual
number of drugs used by population.
 People may not use certain dispensed medicines for
various reasons. However studies on units of drugs
dispensed helps to compare the hypotheses
generated related to drug use like over use or under
use.

Monetary Units
 The most common and generally used practice in estimation of
drug use is to quantify the value of medicines in monetary units
like rupees, dollar, pounds, euros or other similar units.
 This will help to find the percentage of financial burden for
individuals, family, society, organizations or governments for drug
use. It will help for comparisons at various levels from persons to
global.
 A paracetamol tablet may cost one rupee in India can have a cost
of five rupees in the middle east countries and 15 rupees in USA.
In such a situation the measurement of drug use in monetary
units may net help to give a clear picture when countries are
compared.
 However it is useful in comparing within a similar set up. Similarly
a drug may have different dosage forms and strengths in market
and the price may vary for them. Unless corrective measures are
taken there can be errors while estimating the monetary value of
drug use.

Defined Daily Dose (DDD)
 The defined daily dose (DDD) is a statistical measure
of drug consumption, defined by the World Health
Organization (WHO). It is used to standardize the
comparison of drug usage between different drugs or
between different health care environments. The DDD
is not to be confused with the therapeutic dose or with
the dose actually prescribed by a physician for an
individual patient.
 According to WHO “The DDD is the assumed average
maintenance dose per day for a drug used for its main
indication in adults.” If the DDD for a certain drug is
given, the number of DDDs used by an individual
patient or (more commonly) by a collective of patients
is as follows.

Defined Daily Dose (DDD)
 According to WHO “The DDD is the assumed average
maintenance dose per day for a drug used for its main indication in
adults.” If the DDD for a certain drug is given, the number of DDDs
used by an individual patient or (more commonly) by a collective of
patients is as follows.
 Drug usage (DDDs) = Items issued × Amount of drug per
item/DDD
For example take the case of Paracetamol (Acetaminophen) as a
pain killer (analgesic). If it is having a DDD or 3 g, it means that an
average patient who uses Paracetamol as a pain killer (main
indication) uses 3 grams in a day or within a period of 24 hours.
This is equivalent to six standard tablets of 500 mg each. If a
patient consumes 24 such tablets (12 g of paracetamol in total)
over a certain span of time, this equals a consumption of four
DDDs.
Drug usage (DDDs) = 24 × 500 mg/3g = 4.

Advantages and Disadvantages of
DDD
 The DDDs was developed as a standard measure of
drug utilization that solves the problems of number of
prescriptions, units of drugs dispensed and the
monetary units of drug use. However it has certain
limitations.
 The DDD is a technical unit of comparison and many
drugs are not yet assigned the DDDs. Pediatric uses
are often not considered in the calculations.
 Problems can also arise when doses vary widely as in
the case of Aspirin which in low doses are used in
cardiology while high doses are used for inflammatory
conditions.

Prescribed Daily Dose (PDD)
 The prescribed daily dose (PDD) is defined as the
average dose prescribed as calculated from a
representative sample of prescriptions. The PDD
gives the average amount of a drug that is actually
prescribed.
 The PDD can be determined from studies of
prescriptions or medical or pharmacy records. It is
important to relate the PDD to the diagnosis on which
the dosage is based.
 The PDD is useful for validating the DDD. In the case
of drug drugs where the recommended dosage differs
from one indication to another (e.g., the
antipsychotics), it is important to link the diagnosis to
the PDD.
 Pharmacoepidemiological information (e.g., on sex,

Spontaneous reporting
 Spontaneous reports are so called because they take place
instantaneously during the clinical investigation or normal diagnostic
appraisal of a patient, or during a routine administration of medicines
where a drug may be implicated in the causality of an adverse the event.
The spontaneous reporting system is a widely used, effective, and
relatively inexpensive method of collecting information on suspected
ADRs.
 The spontaneous reporting system relies on vigilant physicians and
other healthcare professionals who not only generate a suspicion of an
ADR, but also report it. In many countries, the spontaneous reporting
scheme has been extended to reporting from pharmacists, nurses and
even patients.
 Spontaneous reporting of ADRs from health professionals is important
for detection of signals indicating new ADRs. It is a basic method for post
marketing surveillance. The spontaneous reporting in recent improved
very much when new categories of healthcare providers like clinical

Prescription Event
Monitoring
 Prescription-event monitoring (PEM) is a non-interventional method
for post marketing drug safety monitoring of newly licensed
medicines. PEM as a prescription based monitoring system was
introduced in UK in the 1980s at the Drug Safety Research Unit to
study large cohorts of drug users. Utilizing the distinct structure of
the UK National Health Service (NHS), PEM today enables the
generation and testing of hypotheses regarding drug alerts or
“signals” that may be of public health interest. PEM is a non-
interventional, observational cohort form of pharmacovigilance.
 It is non-interventional in the sense that nothing happens to
interfere with the doctor’s decision regarding which drug to
prescribe for each individual patient. PEM is a hypothesis
generating method like spontaneous ADR reporting. It is also used
for testing hypothesis related to ADR in defined population of drug
users. PEM and Spontaneous reporting constitute the backbone of
the post marketing surveillance techniques developed to survey the
use of newly marketed medicines.

Post Marketing Surveillance
 Post marketing surveillance (PMS) is also known as post
market surveillance. PMS is the practice of monitoring the
safety of a drug or medical device after it has been released
on the market and is an important aspect of
pharmacovigilance. It evaluates drugs taken by individuals
under a wide range of circumstances over an extended
period of time. Such surveillance is much more likely to
detect previously unrecognized positive or negative effects
that may be associated with a drug.
 Drugs are approved for marketing based on the basis of
clinical studies/ trials which involve relatively small numbers
of people who have been selected for this purpose. People
involved in clinical trials normally do not have other medical
conditions which may exist in the general population. PMS
can further refine, or confirm or deny, the safety of a drug
after it is used in the general population by large numbers of
people who have a wide variety of medical conditions.

Record/ Data linkage
Systems
 In the past it was very difficult to maintain the registers and records
in health care for long periods, say beyond 5 years. Though
hospitals were maintaining the case sheets and registers in their
record rooms or library, they were difficult to use after certain period
of time due to damages or decomposition of papers and the
writings. It was difficult to monitor the prescriptions and their
dispensing in hospitals and community pharmacies. The analysis
and compilation of data was very difficult and time consuming.
 With the introduction of computers and the application of information
technology in health care, record keeping and maintenance of
registry became possible and easy. The data analysis and
compilation became quick and perfect. However in India, the
situation is not very much encouraging as the computerisation is yet
to be introduced in many health care centres as well as in a large
majority of Community Pharmacies. The net working is also very
poor in the country in health care. The hospitals are keeping the
data as their private documents due to the absence of agencies to
govern such aspects.

Epidemiological methods
Type of study Alternative name Unit of study
Observational studies
Descriptive studies
Analytical studies
Ecological Correlational Populations
Cross sectional Prevalence Individuals
Case control Case reference Individuals
Cohort Follow up Individuals
Experimental studies Intervention studies
RCT Clinical trials Individuals
Clustered RCT Groups
Field trials / Community
trials
Community intervantion
studies
Healthy people
communities

Case report
Case series
Descriptive
Epidemiology
Descriptive
RCT
Before-After
study
Cross-sectional
study
Case-Crossover
study
Case-Control
study
Cohort study
Analytic
Ecologic study

Study Design Sequence
Case reports Case series
Descriptive
epidemiology
Analytic
epidemiology
Clinical
trials
Animal
study
Lab
study
Cohort Case-
control
Cross-
sectional
Hypothesis formation
Hypothesis testing

Descriptive Studies
Case-control Studies
Cohort Studies
Develop
hypothesis
Investigate it’s
relationship to
outcomes
Define it’s meaning
with exposures
Clinical trials
Test link
experimentally
Increasing
Knowledge
of
Disease/Exposure

Case Reports
 Detailed presentation of a single case or
handful of cases
 Generally report a new or unique finding
e.g. previous un described disease
e.g. unexpected link between diseases
e.g. unexpected new therapeutic effect
e.g. adverse events
 New diagnosis or pathogenesis

Case Series
 Compilation of multiple case reports
 Assesses prevalent disease
 Cases may be identified from a single or multiple sources
 Generally report on new/unique condition
 May be only realistic design for rare disorders
 Cases are not compared to a control group
 Descriptive statistics
 Usually no statistical testing

Case Series Advantages
 Time efficient, less resource intensive
 Uses available clinical data
 Recognizes new diseases
 Rapid hypothesis generation
 Basis for analytic study
 Can launch a case-control study

Case Series Limitations
 Cases may not be representative
 No comparison group or underlying population
represented
 Open to systematic errors

Case Report
Case Series
Descriptive
Epidemiology Study
One case of unusual
injury finding
Multiple cases of
injury finding
Population-based
cases with denominator

Objectives of Case Control Study:
A. Estimation of risk of exposure to various
factors associated with diverse phenomena.
B. To identify the modifiable causal factors.
c. Evolving risk intervention strategies for
prevention and control of public health
problems.

Basic steps in case control study
A. Selection of cases and controls
B .Matching
C. Measurement of exposure
D. Analysis and Interpretation

Selection of cases and controls
Selection of cases:-
a. Definition of case:
-Diagnostic criteria:
-Eligibility criteria:
Sources of cases:
It includes:
1. All the persons with disease seen at
particular medical care facility or group of
facilities in a specified period of time.
2.All the persons with disease found in a
more general population, such as that of city or
country population at a point or in a period of
time.

SELECTION OF CONTROLS:
Controls must be free from disease under
study.
They must be as similar as to the cases,
except for the absence of the disease under
study.
SOURCES OF CONTROLS:
a. Hospital controls
b. Relatives
c. Neighbourhood controls
d. General population

Matching:
Definition: It is defined as 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 and which, if not adequately
matched for comparability, could distort or
confound result the results.
Eg: Age in study of breast cancer
Role of alcohol as etiology of colon cancer
TYPES:
a. Group matching
b. Pair matching

Measurement of exposure
 This may be obtained by
interview, by questionnaires
or by studying past records
of cases such as hospital
record or employment
record.
 Bias or systematic error
should be ruled out.

Analysis
Is final step to find out
A. Exposure rates among cases and controls to
suspected factor.
B. Estimation of disease risk associated with
exposure(odds ratio).
Exposure Rates:
Cases (with lung
cancer)
Controls (without
lung cancer)
Smokers (less than
5 cigarettes a day)
33 (a) 55 (b)
Non smokers 2 (c) 27 (d)
total 35 (a+c) 82 (b+d)

Exposure rates:
Cases=a/(a+c)=33/35=94.2 percent
Controls=b/(b+d)=55/82=67percent
p<0.001
Odds ratio:
• It is a measure of strength of the association between risk
factor and out come.
Disease
Yes No
Exposed a b
Non exposed c d
• Odds ratio= ad/bc
=33x27/55x2=8.1

Estimation of relative risk :
Estimation of disease risk associated with
exposure is obtained by an index known as
‘Relative Risk’ which is defined as
Relative Risk= incidence among exposed
incidence among non
exposed
=a/(a+b)
c/(c+d)

Examples of case- control study
1. Adenocarcinoma of vagina
2. Oral contraceptives and thromboembolic
disease
3. Thalidomide tragedy

Advantages
 Relatively easy to carry out
 Rapid and inexpensive (compared with cohort studies)
 Require comparatively few subjects
 Particularly suitable to investigate rare diseases or diseases
about which little is known. But a disease which is rare in the
general population(e.g. leukemia in adolescents) may not be rare in
special exposure group (e.g. prenatal x rays)
 No risk to subjects
 Allows the study of several different etiological factors (e.g. :
smoking, physical activity and personality characteristics in
myocardial infarction)
 Risk factors can be identified .
 Rational prevention and control programmes can be established
 No attrition problems, because case control studies do not require
follow up of individuals into the future
 Ethical problems minimal

Disadvantages
 Problems of bias. e.g., Relies on memory or past
records, the accuracy of which may be uncertain;
validation of information obtained is difficult or
sometimes impossible
 Selection of an appropriate control group may be
difficult
 We cannot measure incidence, and can only
estimate the relative risk.
 Do not distinguish between causes and associated
factors
 Not suited to the evaluation of therapy or prophylaxis
of disease.
 Another major concern is the representativeness of
cases and controls.

COHORT STUDY(Incidence
study)
• It is also called longitudinal or incidence or forward
looking study.
• A Cohort is defined as group of people who share a common
characteristic or experience within a defined time period .
Distinguishing factors :
a. Cohort are identified prior to appearance of disease under
investigation.
b. Study groups, so defined are observed over a period of
time to determine frequency of disease.
c. Study proceeds forward from cause to effect.

OBJECTIVES OF COHORT
STUDY
Estimating directly risk of exposure to various
factors associated with disease phenomena.
Exploring natural history of disease in entirety and
identifying additional pathological events to complete
natural history.
Identifying appropriate outcome events in natural
history of disease for appropriate intervention for
limitations.
Identify modifiable risk factors.

TYPES OF COHORT STUDY
PROSPECTIVE
STUDY
RETROSPECTIVE
STUDY
COMBINATION OF
PROSPECTIVE
STUDY
RETROSPECTIVE
STUDY

Prospective or current study
It is one in which
outcome has not yet
occurred at the time
of investigation
begins.
Ex: Does exposure to
x(smoking) correlates
with outcome y(lung
cancer)

Retrospective or historical
study
 It is one in which outcome have all
occurred before the start of investigation.
Investigation goes back in time ,
sometimes 10 to 30yr to select his study
groups from existing records of past
employed medical or other records and
traces them forward through time from
past date fixed on records.

Combination of prospective and
retrospective study/Nested cohort
study
 Cohort is defined from past records
and is assessed of date for outcome.
Same cohort is followed up
prospectively into future for further
assessment of outcome.

Nested case-control study of gastric
cancer
 To determine if infection with Helicobacter pylori was associated
with gastric cancer, investigators used a cohort of 128 992 people
that had been established in the mid-1960s.
 By 1991, 186 people in the original cohort had developed gastric
cancer.
 The investigators then did a nested case-control study by selecting
the 186 people with gastric cancer as cases and another 186
cancer-free individuals from the same cohort as controls.
 H. pylori infection status was determined retrospectively from
serum samples that had been stored since the 1960s.
 84% of people with gastric cancer –and only 61% of the controls –
had been infected previously with H. pylori, suggesting a positive
association between H. pylori infection and gastric cancer risk.18

Elements of cohort study
 I.Selection of study subjects:
a. General population
b. Special group
c. Exposed groups

Obtaining data on exposure
a. Cohort Members : Through interviews
b. Review of records: certain kind of
information can be obtained only from
records ex; x-ray dose, type of surgery etc
c. Medical examination or special tests.
d. Environment surveys.

Selection of comparison
groups
a. Internal comparison: within group.
b. External comparison: with other group
c. Comparison with general population.

Follow up
A. Periodic medical examination of each
member
B. Reviewing physician and hospital records
C. Routine surveillance of death records
D. Mailed questionnaires, telephone calls,
home visits etc

Analysis
 Data analyzed in terms of
a. Incidence rates of outcome among exposed
and non exposed.
b. Estimation of risk
A. INCIDENCE RATE:
ex:
CIGARETTE
SMOKING
DEVELOP
LUNG CA
DID NOT
DEVELOP
LUNG CA
TOTAL
YES 70 (a) 6930(b) 7000(a+b)
NO 3(c) 2997(d) 3000(c+d)

Incidence Rates
• Among smokers=70/7000= 10per 1000
• Among non smokers=3/3000=1per 1000
B. Estimation of risk:
a. RELATIVE RISK :
• RR= Incidence Of disease(or death) among exposed
Incidence of disease( or death) among non exposed
ex: RR of lung cancer=10/1=10. implies smokers
are 10 times greater risk of lung cancer than non
smokers.

Attributable risk:
AR=Incidence of disease rate among exposed – incidence
of disease rate among non exposed
__________________________________
Incidence rate among exposed
=10-1 X100=90percent
10_____________
Implies 90percent of lung cancer in smokers is
due to smoking.

Examples of cohort study
1. Smoking and lung cancer
2. The Framingham heart study
3. Oral contraceptives and health

Advantages
 Incidence can be calculated
 Several possible outcomes related to
exposure can be studied simultaneously.
 Cohort studies provide a direct estimate of
relative risk
 Dose response ratios can also be calculated
 Since comparison groups are formed before
disease develops, certain forms of bias can be
minimized like misclassification of individuals
into exposed and unexposed groups

Disadvantages
 Involve a larger number of people. Unsuitable for investigating
uncommon diseases or diseases with low incidence in the
population.
 Takes long time to complete the study.
 Administrative problems like loss of funding , experienced staff
, extensive record keeping are inevitable.
 Attrition of cohort group-due to migration , dropout , loss of
interest and death.
 Difficulties in selection of comparison groups.
 Changes in standard methods and diagnostic criteria during
study.
 Expensive
 Study can alter behavior of cohort study group. E.g.:
smoking and exercise
 Ethical problems.
 Studies only limited factors in the disease causation

Difference between case control and cohort study
Serial no Case control study Cohort study
1 Proceeds from effect to cause. Proceeds from cause to effect.
2 Starts with disease. Starts with people exposed to risk
factors .
3 Tests whether suspected factor occurs
more frequently in those with disease.
Tests whether disease occurs more
frequently in those exposed.
4 Usually first approach to testing
hypothesis.
Reserved for testing of precisely
formulated hypothesis
5 Involves fewer no of subjects Involves larger no of subjects
6 Yields relatively quick results. Long follow up period often needed.
7 Useful for study of rare disease. In appropriate when the disease or
exposure under investigation is rare
8 Generally yields only estimate of RR Yields incidence rates RR as well as
AR
9 Cannot yield information about disease
other than selected for study
Can yield information about more than
one disease
10 Relatively in expensive Expensive.

87
Definition of bias
Any systematic error in an epidemiological
study that results in an incorrect estimate of
the association between exposure and
disease
Systematic variation of measurements
from the true value (Last J.)

88
Types of bias
 Selection bias
 Information bias
 Confounding

EXPERIMENTAL
STUDIES
RANDOMIZED
CONTROL
TRIALS
NON-
RANDOMIZED
TRIALS
Experimental studies

Randomized control trial
It is an epidemiologic experiment made to use
scientific technique to evaluate methods of
prevention & treatment.

Steps of RCT
 Drawing a protocol
 Selecting the reference and study group
 Randomization
 Manipulation and intervention
 Follow up
 Assessment

STEPS IN RCT:
1.Drawing up a protocol:
They are written
guidelines, helps to
minimize bias and
errors in study.
o It includes question to
be answered, criteria
for selection of study,
size of sample,
procedure for allocation
of subjects, treatment to
be applied etc.
o Pilot studies or
preliminary test runs.

2.Selecting reference & study population:
 Reference population is population to which the
findings of the trail if found successful are expected
to be applicable.
 Study population is the actual population that
participates in study.
3.Randomization: It is the heart of RCT. It is a
statistical procedure by which the participants are
allocated into groups called study and control
groups.
It attempts to eliminate bias and allow
for comparability by matching.
4. Manipulation: Done by deliberate application or
withdrawal or reduction of suspected casual factor.

5.Follow up: It is examination of experimental & control group
subjects at defined intervals of time.
6.Assessment: It is the final step of the outcome of trial in terms of
positive & negative results.
Bias may arise due to subject variation, observer bias and
blinding.
Blinding is done to get valid result & to prevent bias. It has 3 types.
1.single blind trial
2.double blind trial
3.triple blind trial.

1.Concurrent parallel study
design
2.Cross over type of study
design.
Some study
designs:

Concurrent and Cross over
study

TYPES OF RCT:
1.Clinical trials: It is concerned with evaluating therapeutic
agents mainly drugs.
The main disadvantage is it takes long time for the
process.
Eg-- Hypertension detection & follow up program on
10500 subjects assigned randomly into 2 groups.
1.Stepped care: Anti-HTN therapy.
2.Refferred care: Subjects are referred to
primary care, physician treated as usual.
Stepped care Referred care
Mortality 9:100 9.7:100
Final BP 84 89

2.Preventive trial or Field
trials: They are the trials of
primary preventive measures
done to prevent or eliminate
disease on experimental basis.
Eg.Trials of vaccines &
chemo-prophylactic agents.
It should be in clear
statement about benefit to the
community, risk involved, cost
to the health services in terms
of money, men & material.

Disease No of children
Measles
Vaccin
ated
Non-
vaccin
ated
Total
yes 40 486 526
no 320 54 374
total 360 540 900
Example for vaccine trial

3.Risk factor trials: A type of preventive trial of risk
factors in which the investigator intervenes to interrupt
the usual sequence in the development of disease for
those who are having risk factors for developing the
disease.
eg.Major risk factors for CHD are elevated blood
cholestrol,smoking & hypertension.
4.Cessation experiments: In this type of study an attempt
is made to evaluate the termination of a habit which is
considered to be casually related to disease.
eg.cigratte smoking & lung cancer one group smokes &
other group give up smoking ,demonstration of

Examples-
1.Uncontrolled trials:
These are trials with no
comparison(controls)
eg.pap test, there is
epidemiological evidence
from these trials that pap
test for Ca cervix is
effective in reducing
mortality.
2.Before & after comparison
studies:
i.Without control.eg.James
Lind studies in preventing
scurvy
ii.With control.Eg.Seat Belt
Legislation inVictoria,
Australia.
Non Randomized control trial

Epidemiology.pptx

Recommended

Recommended

More Related Content

Similar to Epidemiology.pptx

Similar to Epidemiology.pptx (20)

Recently uploaded

Recently uploaded (20)

Epidemiology.pptx