This is the presentation on the topic of measuring the occurrence of disease i.e. incidence, prevalence and mortality and more

1. Measuring the Occurrences of Disease
Presented By : -
Dhan Lal Pandey
Student of GM, Bed, BPH

2. Disease
• A disease is a particular abnormal condition that
negatively affects the structure or function of all or part
of an organism, and that is not due to any immediate
external injury.
• Disease are often known to be medical condition that are
associated with specific signs and symptoms.
• Disease may be caused by external factors such as
pathogen or by internal dysfunctions like immune
system, immunodeficiency, hypersensitivity, autoimmune
diseases etc.

3. Measuring the occurrence of Diseases
Numerator and Denominator:-
- A numerator and denominator are found in fractions, where they are,
respectively, the top and bottom numbers of the fraction.
- In the fraction ¾, 3 is the numerator, and 4 is the denominator which
divides the numerator.
- This same mathematical usage occurs in research, where the result
of a study is usually expressed as a ratio, a compound of numerator
and denominator.

4. Measuring the occurrence of disease
• Measurement of the occurrence of disease is done by different rate,
ratio and proportion.
Rate: -
- Measure the occurrence of some particular event in a population
during a given time period.
- It signifies speed or the frequency of occurrence per unit time.
- Rate = N/D * 100
E.g. IMR, Incidence Rate, Notification rate of sputum smear positive
case= new smear +ve / 1,00,000
&
Cure rate = no. of cases cured/ no. of case under treatment X 100

5. Measuring the occurrence of disease
Ratio:-
- Relation of size between two random quantities.
- The numerators is not a component of denominator
- Ratio= (N/D)* 100,1000……
- E.g. MMR, Sex ratio, doctor-nurse ratio, doctor- people ratio, child
women ratio etc.
- A ratio can be written as one number divided by another (a fraction) of
the form a/b − Both a and b refer to the frequency of some event or
occurrence.

6. Measuring the occurrence of diseases
Proportion:-
- A proportion is a ratio in which the numerator is a subset (or part) of
the denominator and can be written as a/(a+b).
- Proportion= (N/D)*100%
- E.g. CPR, Prevalence rate, Case Fatality Rate etc.

7. Measuring the occurrence of diseases
• Epidemiology focuses, on measurement of mortality and morbidity in
human populations.
• The first requirement is definition of what is to be measured and
establishment of criteria or standards by which it can be measured.
• The basic requirements of measurements are validity, reliability,
accuracy, sensitivity and specificity.
• The clinician may not require a precise definition of disease (e.g.,
migraine) for immediate patient care, but the epidemiologist needs a
definition
(a) That is acceptable and applicable to its use in large populations and
(b)That is accurate and valid, to enable him to identify those who have
the disease from those who do not .

8. Measuring the occurrence of diseases
1. Measurement of Morbidity (Incidence and prevalence rate)
2. Measurement of Mortality (Death)
3. Measurement of Disability
4. Measurement of Natality (Birth rate)
5. Measurement of the presence, absence or distribution of the disease
6. Measurement of medical Needs
7. Measurement of presence , absence or distribution of causes of
diseases
8. Measurement of demographic variables (Gender, Race, Marital Status,
Age, Education Status, Family size etc).

9. Measuring The Occurrence Of Diseases
Morbidity Measuring (Incidence
and Prevalence)
1. Incidence proportion/ attack
rate/ risk
2. Secondary attack rate
3. Incidence rate or person time
rate
4. Point prevalence rate
5. Period prevalence rate
6. Life time prevalence Rate
Mortality Measuring (Death)
1. Crude death rate
2. Death to case ratio
3. cause specific death rate
4. Sex specific Mortality rate
5. Race specific Mortality Rate
6. Age-specific death rate
a) Neonatal mortality rate
b) Post natal mortality rate
c) Infant mortality rate
d) Maternal mortality rate

10. Morbidity Measuring
1. Incidence proportion/ attack rate/ risk
2. Secondary attack rate
3. Incidence rate or person time rate
4. Point prevalence rate
5. Period prevalence rate
6. Lifetime prevalence rate

11. Incidence
• Incidence refers to the occurrence of new cases of disease or
injury in a population over a specified period of time i.e. around
2000 peoples attempt suicide during lockdown in Nepal.
• The number of new cases in a community
• others use incidence to mean the number of new cases per unit
of population.
Two types of incidence are commonly used — incidence
proportion and incidence rate.
Synonyms for incidence proportion :-
• Attack rate
• Risk
• Probability of developing disease
• Cumulative incidence

12. Incidence Proportion/ Risk/ Attack rate
• Incidence proportion is the proportion of an initially disease-free
population that develops disease, becomes injured, or dies during
a specified (usually limited) period of time.
• Method for calculating incidence proportion (risk):- Number of
new cases of disease or injury during specified period / Size of
population at start of period

13. Incidence Proportion
• EXAMPLES: Calculating Incidence Proportion (Risk)
• Example A: In the study of diabetics, 100 of the 189 diabetic men died during
the 13-year follow-up period. Calculate the risk of death for these men.
• Numerator = 100 deaths among the diabetic men
Denominator = 189 diabetic men
10n = 102 = 100
• Risk = (100 ⁄ 189) × 100 = 52.9%
• Example B: In an outbreak of gastroenteritis among attendees of a corporate
picnic, 99 persons ate potato salad, 30 of whom developed gastroenteritis.
Calculate the risk of illness among persons who ate potato salad.
• Numerator = 30 persons who ate potato salad and developed gastroenteritis
Denominator = 99 persons who ate potato salad
10n = 102 = 100
• Risk = “Food-specific attack rate” = (30 ⁄ 99) × 100 = 0.303 × 100 = 30.3%

14. Incidence rate or person time rate
• Incidence is the rate of new (or newly diagnosed) cases of the
disease.
• It is generally reported as the number of new cases occurring
within a period of time (e.g., per month, per year).
• It is more meaningful when the incidence rate is reported as a
fraction of the population at risk of developing the disease (e.g.
per 100,000 or per million population).
• Incidence rates can be further categorized according to different
subsets of the population – e.g., by gender, by racial origin, by
age group or by diagnostic category.

15. EXAMPLES: Calculating Incidence Rates (Continued)
• Example 1 : In 2003, 44,232 new cases of acquired immunodeficiency
syndrome (AIDS) were reported in the Nepal. The estimated mid-year
population of the Nepal in 2003 was approximately 2, 64,
94,523.Calculate the incidence rate of AIDS in 2003.
• Numerator = 44,232 new cases of AIDS
Denominator = 2,64,94,523 estimated mid-year population
10n = 100,000
• Incidence rate = (44,232 ⁄ 2,64,94,523) × 100,000
= 166.94 new cases of AIDS per 100,000 population

16. Secondary attack rate
• A secondary attack rate is sometimes calculated to document
the difference between community transmission of illness versus
transmission of illness in a household, barracks, or other closed
population. It is calculated as:
• Number of cases among contacts of primary cases / Total
number of contacts × 10 n
• Often, the total number of contacts in the denominator is
calculated as the total population in the households of the primary
cases, minus the number of primary cases.
• For a secondary attack rate, 10n usually is 100%.

17. Calculating Secondary Attack Rates
• EXAMPLE: Calculating Secondary Attack Rates
• Consider an outbreak of shigellosis in which 18 persons in 18
different households all became ill. If the population of the
community was 1,000, then the overall attack rate was 18 ⁄ 1,000
× 100% = 1.8%. One incubation period later, 17 persons in the
same households as these “primary” cases developed shigellosis.
If the 18 households included 86 persons, calculate the
secondary attack rate.
• Secondary attack rate = (17 ⁄ (86 − 18)) × 100% = (17 ⁄ 68) ×
100% = 25.0%

18. Prevalence
• Point prevalence is a measure of the proportion of people in a population who
have a disease or condition at a particular time, such as a particular date.
• It can be used for statistics on the occurrence of Chronic diseases.
• Prevalence = Number of existing cases on a specific date ÷ Number of people in
the population on this date
• Period prevalence is the proportion of the population with a given disease or
condition over a specific period of time. It could describe how many people in a
population had a cold over the cold season in 2006, for example. It is expressed
as a percentage of the population and can be described by the following formula:
• Period prevalence (proportion) = Number of cases that existed in a given period ÷
Number of people in the population during this period
• Lifetime prevalence (LTP) is the proportion of individuals in a population that at
some point in their life (up to the time of assessment) have experienced a "case",
e.g., a disease; a traumatic event; or a behavior.

19. Mortality Measuring
1. Crude death rate
2. Death to case ratio
3. cause specific death rate
4. Sex specific Mortality rate
5. Race specific Mortality Rate
6. Age-specific death rate
a) Neonatal mortality rate
b) Post natal mortality rate
c) Infant mortality rate
d) Maternal mortality rate

20. Crude Death Rate (CDR)
• The crude Death rate is the mortality rate from all causes of death
for a population.
• In the United States in 2003, a total of 2,419,921 deaths
occurred.
• The estimated population was 290,809,777.
• The crude mortality rate in 2003 was, therefore, (2,419,921 ⁄
290,809,777) × 100,000, or 832.1 deaths per 100,000 population.
• Target Was 6/1000 according to SLTHP

21. Cause specific Mortality rate
• The cause-specific mortality rate is the mortality rate from a
specified cause for a population.
• The numerator is the number of deaths attributed to a specific
cause.
• The denominator remains the size of the population at the
midpoint of the time period.
• The fraction is usually expressed per 100,000 population.
• In the United States in 2003, a total of 108,256 deaths were
attributed to accidents (unintentional injuries), yielding a cause-
specific mortality rate of 37.2 per 100,000 population.

22. Age Specific Mortality Rate
• An age-specific mortality rate is a mortality rate limited to a
particular age group.
• The numerator is the number of deaths in that age group.
• The denominator is the number of persons in that age group in
the population.
• In the United States in 2003, a total of 130,761 deaths occurred
among persons aged 25–44 years, or an age-specific mortality
rate of 153.0 per 100,000 25–44 year olds.

23. Some Age Specific Mortality rate are:-
Infant mortality rate:-
• The infant mortality rate is perhaps the most commonly used
measure for comparing health status among nations.
• It is calculated as follows:
• Number of deaths among children < 1 year of age reported during
a given time period / Number of live births reported during the
same time period and Multiply by 1,000
• In Nepal IMR was 32 per 1000 according to annual report of
DoHS 2073/74

24. Some Age Specific Mortality rate are:-
Neonatal mortality rate :-
• The neonatal period covers birth up to but not including 28 days.
• The numerator of the neonatal mortality rate therefore is the number
of deaths among children under 28 days of age during a given time
period.
• The denominator of the neonatal mortality rate, like that of the infant
mortality rate, is the number of live births reported during the same
time period.
• The neonatal mortality rate is usually expressed per 1,000 live births.
In 2003, the neonatal mortality rate in the United States was 4.7 per
1,000 live births.
• In Nepal NMR was 21 per 1000 according to annual report of DoHS
2073/74

25. Some Age Specific Mortality rate are:-
Postneonatal Mortality Rate:-
• The postneonatal period is defined as the period from 28 days of
age up to but not including 1 year of age.
• The numerator of the postneonatal mortality rate therefore is the
number of deaths among children from 28 days up to but not
including 1 year of age during a given time period.
• The denominator is the number of live births reported during the
same time period.
• The postneonatal mortality rate is usually expressed per 1,000
live births. In 2003, the postneonatal mortality rate in the United
States was 2.3 per 1,000 live births.

26. Some Age Specific Mortality rate are:-
Maternal mortality rate :-
• The maternal mortality rate is really a ratio used to measure mortality
associated with pregnancy.
• The numerator is the number of deaths during a given time period
among women while pregnant or within 42 days of termination of
pregnancy, irrespective of the duration and the site of the pregnancy,
from any cause related to or aggravated by the pregnancy or its
management, but not from accidental or incidental causes.
• The denominator is the number of live births reported during the same
time period.
• Maternal mortality rate is usually expressed per 100,000 live births. In
2003, the U.S. maternal mortality rate was 8.9 per 100,000 live births.
In Nepal MMR was 254 per lakh live births according to annual report
of DoHS 2073/74

27. Sex Specific Mortality Rate
• A sex-specific mortality rate is a mortality rate among either males
or females.
• Both numerator and denominator are limited to the one sex.
Race-specific mortality rate:-
• A race-specific mortality rate is a mortality rate related to a
specified racial group.
• Both numerator and denominator are limited to the specified race.

28. References
1. Centre for Disease control and Prevention, US Department of Health
and Human services
2. Park’s Textbook of PREVENTIVE AND SOCIAL MEDICINE 24th edition
3. Wikipedia
4. Annual report of DoHS 2073/74

29. - any Questions …?
Thank you..!