This document discusses different measures of morbidity including frequency, duration, and severity. Frequency is measured by incidence and prevalence. Incidence refers to new cases in a defined time period, while prevalence refers to all current cases. Duration is measured by disability rate and severity by case fatality rate. The document provides definitions and formulas for calculating incidence rate, point prevalence, and period prevalence. It also discusses factors that influence prevalence and the relationship between incidence and prevalence.

1. Dr. Anjali Wagh
Professor & HOD
Dept. of Community Medicine
D.Y.Patil Medical College, Kolhapur

2. Measurement of Morbidity
 “ Any departure, subjective or objective,
from a state of physiological well-being”
 Sickness, illness, disability
Morbidity measured in 3 units.
 Frequency - Incidence & prevalence
 Duration - Disability rate
 Severity – Case fatality rate.

3. Morbidity measured in 3 units
Frequency -
Incidence & Prevalence
Duration - Disability rate
Severity – Case fatality rate

4. Uses of Morbidity data
• Describe the disease load in the community &
assist in establishment of priorities.
• Provide more comprehensive, accurate &
clinically relevant data essential for basic
research
• Monitoring & Evaluation of disease control &
prevention activities.

5. Incidence
 “ The number of New cases occurring in a defined
population during a specified period of time”
Number of new cases of specific disease
during a given time period
Incidence Rate = -------------------------------------- X 1000
Population at risk during that period
500
IR = ------ X 1000 = 16.7 per 1000 per year
30,000

6. Incidence Rate
Incidence rate refers –
 Only to New cases
 During a given period ( usually one year )
 Population at risk
 New spells or episodes of disease in a given
period of time per 1000 population.

7. Special Incidence rates
 Attack rate = No. of new cases of disease during
specified time period
----------------------------------------- x 100
Total population at risk during
same period.
 It is the percentage of population at risk , getting the
disease .

8. Secondary attack rate:
 The number of exposed persons developing the
disease within the range of Incubation period
following exposure to a primary case.
 e.g. In family of 6 persons, consisting of 2 parents
(immune) & 4 children, susceptible to chickenpox, one
child develops chickenpox & after sometimes 2
children develop among three.
 SAR = 2 / 3 X 100 = 66 %

9. Uses of incidence rate
Useful for taking action
 A) to control disease
 B) for research into etiology and pathogenesis,
distribution of diseases, efficacy of preventive &
therapeutic measures

10. Prevalence
 All current cases (old & new) existing at a given
point of time, or over a period of time in a given
population
 Definition: The total number of all individuals
who have an attribute or disease at a particular time
divided by the population at risk of having the
attribute or disease at this point in time or midway
through the period
 Two types – Point prevalence
Period prevalence

11. Point Prevalence
 Point prevalence:- the number of all current (old and
new) cases of a disease at one point in time in
relation to a defined population.
Number of all current (old &new) cases of
specific disease existing at a given time period
= ----------------------------------------------------------- X 100
Estimated Population at the same point of time

12. Period prevalence
 Period prevalence: -the number of all current (old and
new) cases existing during a defined period of time
expressed in relation to a defined population.
Number of existing cases (old &new) cases of a
specified disease during a given period of time interval
= -------------------------------------------------------- X 100
Estimated mid-interval Population at risk

13. Case -1
Case -3
Case -5
Case -6
Case -8
Case -2
Case -4
Case -7
case 9
Jan. 1 Dec. 31

14.  Incidence (cases ) – 3, 4 ,5, & 8
 Point prevalence ( Jan 1st) – 1 ,2, 7 & 9
 Point prevalence (Dec 31st) – 1, 3, 5 , 8 & 9
 Period prevalence ( Jan – Dec ) cases -
1, 2, 3, 4 ,5, 7 , 8 & 9

19. Relationship between
Incidence and Prevalence

20. P = I X D
= Incidence X mean duration
Incidence = P / D
Duration = P / I
Relationship between
Incidence and Prevalence

21. Factors influencing observed prevalence rate
• Longer duration of the disease
• Prolongation of life without cure
• Increase in new cases (incidence / risk)
• Out-migration of non-diseased people
• In-migration of susceptible/diseased people
• Improved diagnostic &/or reporting

22. Relationship between
Incidence and Prevalence

23. Factors influencing observed prevalence rate
• Shorter duration of the disease
• Increased case-fatality rate
• Decrease in new cases (incidence / risk)
• In-migration of “healthy” people
• Out-migration of diseased people
• Improved cure rate

24. Relationship between
Incidence and Prevalence

25. Uses of prevalence
 Helps to estimate the magnitude of health
problem / disease in the community.
 Identify potential high risk population.
 Useful for administrative & planning
purposes.