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2. Define Epidemiology
• 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

3. Specific Learning Objectives
• At the end of the session, the students shall be able to
List the basic measurements in epidemiology
Select an appropriate tools ofmeasurement
Measure morbidity &mortality
Perform standardization ofrates

4. Basic measurements in
epidemiology

5. Basic measurements inepidemiology
• Measurements ofmortality
• Measurements ofmorbidity
• Measurements ofdisability
• Measurements ofnatality
• Measurements of the presence, absence or distribution of the characteristics or
attributes of thedisease

6. Basic measurements inepidemiology
• Measurements of the presence, absence or distribution of the
environmentaland other factorssuspected of causing the disease.
• Measurements of the medical needs, health care facilities, utilization of health
services and other factorssuspected of causing the disease.
• Measurements of demographicvariables.

7. Tools of measurement

8. Tools of measurement
1. Rates
2. Ratios
3. Proportions

9. 1. Rate
• A rate measures the occurrence of some particular event (development of disease or
theoccurrenceofdeath)inapopulation during given timeperiod.
•Eg:
CDR = No.ofdeathsin one year
×1000
Mid yearpopulation
• Consists :Numerator, denominator, time factorandmultiplier.

10. Various categories ofrates
a) Crude rates: These are the actual observed rates such as the birth and death rates.
(unstandardized rates)
b) 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 weeklyrates).
c) Standardized rates: These are obtained by direct or indirect method of
standardization or adjustment,e.g.Age and Sex standardized rates.

11. 2. Ratio
• It expresses a relation in size between two random quantities
• The numerator is not a component of the denominator.
• E.g.X:Y or X/Y
• Sex ratio, child-woman ratio, doctor- populationratio
The no. of cjhildren with scabies at a certain time
The no. of children with malnutrition at a certain time

12. 3. Proportion
• A proportion is a ratio which indicates the relation in magnitude of a part of
thewhole.
• The numerator is always included indenominator.
• The proportion is usually expressed in percentage.
The no. of children with scabies at a certain time
Total no. of children in a village at the same time

13. Concepts of numerator and denominator
• Numerator – the no. of times of event has occurred in a
population, during a specified time period.
• Denominator
Related to the population- Mid year population and
population at risk, person time
Related to the total events

14. Measurements ofmortality

15. 1. Crude deathrate
• CDR is the number of deaths (from all causes) per 1000 estimated mid
year population in one year
,in a given place.
CDR = No. of deaths in one year 1000
Mid yearpopulation
• Limitation of CDR is exposed, when we compare age-specific death
rates b/w two populations.
• Major disadvantage of CDR is that they lack comparability for
communities populations that differ by age, sex, race,etc.

16. 2. Specific death rate(SDR)
No.of deaths
SDR= * 1000
Mid year population
• Usefulwhen planning tofindout etiology:
• Cause or disease specific e.g.TB,Cancer,etc.
• Relatedto specific groups- age specific,sexspecific,etc.
• Advantages: It helps us to identify particular groups or groups at risk for preventive action. They
permit comparisonsb/wdifferent causes with in samepopulation
• Disadvantages: mainly used in developed countries where they have civil registration system.

18. 3. Case fatality rate(CFR)
•CFR = T
otal no. of deaths due to particular disease×100
T
otal no. of cases due to the same disease
• It represents the ratio of death to cases
• Virulence of organism & killing power of a disease
• Useful in acute infectious diseases e.g.cholera,measles
• Time interval is notspecified

19. • Proportional mortality rate expresses the number of deaths due to a
particular cause (or in a specific age group) per 100 (or 1000) total
deaths.
• 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 datais not available
• Depends upon only two variables, which differ. So, it cannot be used for
comparison b/wpopulation groups or differenttime periods.
4. Proportional mortality rate(ratio)

20. 4. Proportional mortality rate(ratio)

21. 5. Survival rate(SR)
• It is the population of survivors in a group studied and followed over a period. e.g.for 5 years
period
SR = T
otalno. of patients alive after 5 years ×100
T
otalno. of patients diagnosed ortreated
• Helps in describing prognosisin certain disease and Can be used as a yard stick for the
assessment of standards of therapy.

22. 6. Adjusted or standardizedrates
• It’s major advantage is able to compare death rates of two populations
with different age-composition.
• This is because rates are only comparable if the populations upon which
they are based arecomparable.
• It removes the confounding effect of different age structures and yields a
single standardized or adjusted rate by which we can compare mortality
directly

24. Answer the following

25. 1. 15,231 total deaths in New Mexico during calendar year
2006. 2,010,787 is a estimated 2006 mid-year population
for New Mexico. Can u identify what type of mortality is
this?
Ans:

26. 1. 15,231 total deaths in New Mexico during calendar year
2006. 2,010,787 is a estimated 2006 mid-year population
for New Mexico. Can u identify what type of mortality is
this?
Ans: CRUDE DEATH RATE
2. Someone being unhealthy is called as
Ans:

27. 1. 15,231 total deaths in New Mexico during calendar year 2006.
2,010,787 is a estimated 2006 mid-year population for New
Mexico. Can u identify what type of mortality is this?
Ans: CRUDE DEATH RATE
2. Someone being unhealthy is called as
Ans: Morbidity
3. ………….expresses a relation in size between two random quantities

28. 1. 15,231 total deaths in New Mexico during calendar year 2006.
2,010,787 is a estimated 2006 mid-year population for New
Mexico. Can u identify what type of mortality is this?
Ans: CRUDE DEATH RATE
2. Someone being unhealthy is called as
Ans: Morbidity
3. ………….expresses a relation in size between two random quantities
Ans: Ratio
4. Death rates due to specific causes, specific groups or age is called as…

29. 1. 15,231 total deaths in New Mexico during calendar year 2006.
2,010,787 is a estimated 2006 mid-year population for New
Mexico. Can u identify what type of mortality is this?
Ans: CRUDE DEATH RATE
2. Someone being unhealthy is called as
Ans: Morbidity
3. ………….expresses a relation in size between two random quantities
Ans: Ratio
4. Death rates due to specific causes, specific groups or age is called as…
Ans: Specific death rates

30. Measurements ofmorbidity

31. Measurements of morbidity
•Morbidity is defined as “anydeparture,subjectiveor objective,
from a stateof physiologicalwell-being”.
•Morbidity rates/ratiosmeasuredby
a) Frequency of disease: incidence and prevalence
b) Duration of illness: days,months and years
c) Severity of illness: case fatalityrates

32. Importance of morbiditydata
• T
o know extent and nature of the disease load in community and
help in formingpriorities.
• Provide more comprehensive and accurate and clinically relevant
information on patient characteristics – 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.

33. Measurements of morbidity
focuses on incidence and
prevalence rates, which are
widely used to describe disease
occurrence in a community
Measurements of morbidity

34. INCIDENCE

35. Incidence
Incidence is defined as “the number of new cases
occurring in a defined population during a specific period of
time.
•It is given by formula

36. SPECIAL INCIDENCE RATE
• Attack rate (case rate) andSecondary attack rate
• Attack rate: An attack rate is an incidence rate (usually expressed as
a percent), used only when the population is exposed to risk for a
limited period of time such as during an epidemic.

37. Secondary attack rate
It is defined as the number of exposed persons developing the
disease within the range of the incubation period following exposre to a
primary case.
Uses of incidence rate:
• Tocontrol disease,and
• For research into aetiology and pathogenesis, distribution of diseases, and
efficacyof preventive and therapeuticmeasures.

38. 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.
• Prevalenceis a ratio but expressed as a rate
• Two types
• Pointprevalence
• Period prevalence

39. Point prevalence
It defined as the number of all current cases (old &
New) of a disease at one point of time, in relation to a
defined population.

40. Period prevalence
It measures the frequency of all current cases (old &
New) existing during a defined period of time(eg.Annual
prevalence) expressed in relation to d defined population.

41. Relationship between prevalence &incidence
• Prevalence depends upon two factors: the incidence and duration of
illness. It can be expressed a P= Incidence (I) X Mean Duration (D)
• (ifpopulation is stable and incidence and duration are unchanging)
• Longer the duration:greateris the prevalence ratee.g.TB
• Acute disease: short duration and rapid recovery. So prevalence is less than
incidence.

42. Uses ofprevalence
• Estimating magnitude of health/ disease problems in the
community
• Identify potential risk populations
• Useful for administrative and planningpurposes

44. ASSIGNMENT ON DIFFERENCE BETWEEN
INCIDENCE AND PREVALENCE

47. ANSWER

48. Any Questions???