measurement of morbidity (prevalence ) presentation by dr. sadhana, sms medical college , jaipur included all aspects related to prevalence - objectives,types,significance ,comparison between prevalence and incidence , practical example of prevalence.

1. MESUREMENT OF
MORBIDITY (PREVALENCE)
Dr. Sadhana meena Guided by:
MD (first year resident) Dr. Rajeev yadav (Associate prof.)
Department of community medicine Department of community medicine
SMS Medical college & hospital SMS medical college & hospital

2. OBJECTIVE
 DEFINE: EPIDEMIOLOGY,MORBIDITY,PREVALENCE
 DIFFRENTIATE BETWEEN POINT PREVALENCE AND PERIOD
PREVALENCE
 SIGNIFICANCE OF PREVALENCE
 PROBLEM WITH PREVALENCE
 RELATIONSHIP BETWEEN PREVALENCE AND INCIDENCE
 COMMON PREVALENCE TERMS
 COMPARISON OF PREVALENCE AND INCIDENCE
 CALCULATE PREVALENCE

3. Epidemiology:
 The study of the distributions and determinants of
health related states or events in specified population
and the application of this study to control health
problems.

4. Morbidity:
 Morbidity has been defined as “any departure,
subjective or objective, from a state of physiological
well being”
 The term is used equivalent to such terms as sickness,
illness, disability etc.

5. MESUREMENT OF MORBIDITY:
WHO expert committee on health statistics noted in its 6th
report that morbidity could be measured in terms of 3 units-
1. Persons who were ill
2. The illness (periods or spells of illness) that these persons
experienced
3. the duration (days,weeks,etc)of these illnesses .
These three aspects are commonly measured by morbidity
rate or ratio namely,
1. Frequency
2. Duration
3. severity

6. 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.

7. PREVALENCE
• Prevalence is defined as the number of affected persons
present in the population at a specific time divided by
the number of persons in the population at that same
time
no.cases of a disease present in the
population at a specified time
Prevalence rate: ×1000
no.of persons in the population at
that specified time
 Although referred to as a rate , prevalence rate is really a ratio.

8. Example
In 2001 , madhyapradesh (M.P) reported an estimated 253,040
residents over 20 yrs of age with diabetes and According to
india census that in 2001 M.P population over 20 was
5008,862.calculate prevalence?
Prevalence - 253,040 ×1000 = 5.1%
5008,862
-Can also be expressed as 51 cases per 1000 residents over 20
years of age

9. Types of prevalence-
1.POINT PREVALENCE
2.PERIOD PREVALENCE

10. Point Prevalence:
It is defined as number of all current cases (old and new)
of a disease at one point of time, in relation to a defined
population. The point in a point prevalence, may for all
practical purposes consists of a day, several days or even a
few weeks depending upon the time it takes to examine
the population sample. For eg. Do you currently have T.B?
PP = no of all cases (old & new) of a specified disease existing at a given point
in time X 100
Estimated population at the same point in time
• When term ” prevalence rate ” is used , without any further
qualification , it is taken to mean “point prevalence”

11. Period Prevalence:
Period prevalence measures the frequency of all current cases (old and new)
existing during a defined period of time. e.g (Annual Prevalence) expressed
in relation to defined population.
It includes cases arises before but extending into or through to the year as
well as those cases arising during the year. Eg have you had TB in DURING
last years?
Period P = no of all cases (old & new) of a specified disease during a given period of
time interval ×100
estimated mid year population at risk

12. No.Of casesofadiseasebeginning,developing&ending
duringaperiodoftime
Jan Dec
case1
case 2 case 3
case 4 case5
case6
case7 case8

13. where: denote start of illness
denote duration of illness
According to this figure:
A. Incidence would include cases – 3,4,5 and 8
B. Point prevalence (jan1) cases-1,2 and 7
C. Point prevalence (dec31) cases-1,3,5 and 8
D. Period prevalence cases(jan to dec) -1,2,3,4,5,7 and 8

14. EXAMPLE
• Suppose we followed a population of 150 persons for one year
and 25 people had a disease of interest at the start of follow
up and another 15 new cases developed during the year.
Q. What is the period prevalence for the year?
PP=(25+15)/150=0.27 or 27%
Q. What is the point prevalence at the start of the period?
P= 25/150=.017 or 17%

15. Factorsaffectingprevalencerate:
Increasedby-
1) duration of disease
2) Prolongation of life of patients without cure
3) Increase new cases(incidence)
4) In-migration of cases
5) Out-migration of healthy people
6) In- migration of susceptible people
7) Improved diagnostic facilities(better reporting)

16. And decreasedby:
1) Shorter duration of disease.
2) High case –fatality rate from disease.
3) Decrease in new cases (incidence)
4) In-migration of healthy people
5) Out-migration of cases
6) Improved cure rate of cases

17. Significance of prevalence
• Prevalence is important and useful measure of the
burden of disease (magnitude of health disease)in
community.
• Prevalence is valuable for planning health
services(monitoring & evaluation of disease control
activities)
• Prevalence also use to make future projection and
anticipate the changes that are likely to take place in the
disease burden.
• Prevalence may be suggestive if not confirmatory in
studies of etiology of certain disease eg .asthma in
children.

18. Problems with prevalence
measurements
1. Problems with numerators-
 A) defining who has the disease(no precise definition
used for a case)
B) which person should be included in the
numerator(data obtained from interview ,have potential
limitation like problem due to difficulty in diagnosis ,
problem associated with participant and problems
associated with the interviewer.
2 .Problem with denominators-
Sometimes selective undercounting of certain groups in
the population may occur (inclusion or exclusion criteria)

19. ..contd
3. Problem with hospital data-
Data from hospital records are one of the most important
sources of information in epidemiologic studies however some
problems are there like-
A) hospital records are not designed for research but
rather for patient care.
B) people at risk (denominator)is generally not
defined(different hospital area has different catchment
area)
C) hospital admission are selective(personal
characteristic ,severity of disease , admission policies and
associted conditions)

20. Relationship between prevalence and
incidence
Prevalence =incidence × time
For eg. If incidence is 20 cases per 1000 population per year
mean duration of disease is 7 year
then prevalence = 20× 7= 140 per 1000 population

23. Some common prevalence terms-
1. Sero-prevalence-
seroprevalence is the no. of person in a
population who test positive for a specific disease
based on serology(blood serum) specimens
eg. sero prevalence of dengue

24. 2. Lifetime prevalence-
Lifetime prevalence is the proportion of a population that ,
at some point in their life , has experienced a particular
health event , risk factor or disease .
For eg. In a survey , you might be asked if you have ever
smoked . lifetime prevalence is calculated by comparing
the number of people found to have experienced the
health event with the total no. of people studied.

25. • 3. Disease rate at autopsy-
no. of cases of a disease ×100
numbers of persons autopsied
• 4. Birth defect rate -
numbers of babies with a given abnormality ×100
number of live birth

26. Comparison of incidence and
prevalence:
Incidence
i. Probability of developing
disease
ii. Numerator counts only
new cases
iii. Requires follow up of
individuals in a population
to identify new cases
iv. Does not depend on the
duration of illness
v. Preferred measure when
studying cause and effect
Prevalence
i. Probability of already
having disease
ii. Numerator counts both
new and old cases
iii. Does not require follow up
iv. Depends on duration of
disease(long duration will
eventually increase the
prevalence of a disease)
v. Preferred measure when
estimating the population
based burden of a chronic
disease or Attribute (eg.
smoking)

27. EXERCISE-
A study starts with 5,000 people of these
125 have disease in question ,what is
prevalence rate of disease per 1,000
population ?

28. PR= 125 ×1000 = 25
5000
can also say 25 per 1000 population