PSM PRESENTATION TOOLS of Measurement Corrected 2.pptx

Department of Community Medicine
Pt. Jawaharlal Nehru Memorial Medical College, Raipur (C.G.)
TOOLS OF MEASUREMENT
IN EPIDEMIOLOGY
Presented by:
Sanskar Gupta (131)
Sanya Maske (132)
Satyam Sahu(133)
Satyam Tembhare(134)
Saurabh Meshram(135)
Guided By:
Dr. Nirmal Verma
Professor & HOD
Department of Community
Mentor:
Dr. Sandeep Agrawal
Assistant Professor
Department of Community
Medicine

DEFINITION
“The study of the occurrence and distribution of health related
events, states, and processes in specified populations, including
the study of the determinants influencing such processes, and
the application of this knowledge to control relevant health
problems.”(1)
Joaquín de Villalba
John Snow
Joaquin de Villalba

1. Disease frequency
COMPONENTS OF EPIDEMIOLOGY:-
2. Distribution of disease
3. Determinants of disease

Rate:
• A rate measures occurrence of some particular event in a
defined population during a given time period.
• It indicates the change in some event that takes place in a
population over a period of time.
Death rate = ———————————— x 1000
Number of deaths in one year
Mid year population
Tools of measurement in epidemiology

Concept of Numerator and Denominator
Numerator
• The number of times an event has occurred in a
population, during a specified time- period.
Denominator
• Related to the population like -
(a) Mid year population
(b) Population at risk
(c) Person-Time
(d) Person-distance
(e) Sub-groups of population
• Related to total events

Categories of rate
• Crude rate - actual observed rate , Also known as unstandardised rate
Eg.- Death rate & Birth rate.
• Specific rate - Actual observed rates due to specific cause.
Eg- Tuberculosis; or occurring in specific group, Age-sex groups ; or
during specific time periods ,Annual, monthly or weekly time periods.
• Standardised rates - Obtained by direct or indirect method of
standardisation or adjustment.
Eg- Age & Sex standardised rates.

Ratio
• It expresses a relation in size between two random quantities.
• Numerator and denominator may involve an interval of time or
may be instantaneous in time.
• Ratio is a result of dividing one quantity by another.
x:y or x/y
Eg-
• ratio of WBC relative to red blood cells is 1:600 or 1/600.
• Sex ratio, doctor-population ratio

Proportion :
• It is a ratio which indicates the relation in magnitude of a part
of the whole.
• Numerator always included in the denominator.
• Usually expressed as percentage.
• Example:-
The number of children with scabies at a certain time
——————————————————————————————————- X 100
The total number of children in the village at the same time

MEASUREMENT OF MORTALITY
Mortality data provide starting point for many epidemiological
studies.
Each year, information on death is analysed and the resulting
tabulation are made available by each government.
The basis of mortality data is the Death Certificate.

MORTALITY RATES AND RATIOS
Crude death rate - number of deaths during the year * 1000
Mid year population
● Defined as the number of deaths ( from all causes ) per 1000
estimated mid year population in one year, in a given place (1)
● Crude death rate summarises the effect of two factors :
1. Population composition
2. Age specific death rates ( which reflect the
probability of dying

● Limitations - they lack the comparability for communities
with populations that differ by age, sex, race, etc.
● Advantages - they should be examined first as they have the
ability to portray an impression in a single figure

Specific death rates
● They may be :
1. Cause or disease specific - TB, cancer, accident
etc.
2. Related to specific groups - age-specific, sex specific etc.
● Helps to identify groups that are “at risk”, for preventive
action
● Permit comparison between different causes of death within
population.

Case fatality rate
● CFR = total number of deaths due to a particular disease * 100
Total number of cases due to the same disease
● It represents the killing power of a disease, closely related to
virulence
Survival rate
● Proportion of survivors in a group studied and followed over a
period
● Survival rate = total number of patients alive after 5 years * 100
Total number of patients diagnosed or
treated

Proportional mortality rate
proportion of total deaths due to a particular cause or what
proportion of deaths are occurring in a particular age group
● Proportional mortality from a specific disease =
Number of deaths from the specific disease in a year * 100
Total deaths from all causes in that year
● Under-5 proportionate mortality rate =
Number of deaths under 5 years of age in a given year * 100
Total number of deaths during the same period

Total deaths of all age groups in that year
Number of deaths of person aged 50 years and above * 100
● Proportional mortality rate for aged 50 years and above =

Standardisation
● If we want to compare two populations we cannot use crude
death rate as there is different age composition, also it is
cumbersome to use a series of age specific death rate,
therefore we use standardisation
● Direct standardisation : in this we calculate the age specific
death rate per 1000 population of a city, then we apply these
rates to a standard population to obtain the expected deaths
and the standardisation or age adjusted death rate

● Indirect standardisation: in this we find out the standard
mortality ratio that is a ratio of the total number of deaths that
occur in the study group to the number of deaths that would
have been expected to occur if that study group had
experienced the death rates of a standard population
● SMR = observed deaths * 100
Expected deaths
● If the ratio has a value greater than 100 then the population
would appear to carry a greater mortality risk than that of the
whole population

MEASUREMENT OF MORBIDITY
Morbidity is 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.
Morbidity could be measured in terms of 3 units
1) Person who will ill
2) The illness that these person experienced
3) Duration of these illness.

INCIDENCE
● The incidence is defined as “ the number of new cases occurring in a defined
population during a specified period of time”.

SPECIAL INCIDENCE RATES
ATTACK RATE:
● It is an incidence rate, used only when the population is exposed to risk
for a limited period of time such as during an epidemic.
. SECONDARY ATTACK RATE:
It is defined as number of exposed person developing disease within the
range of the incubation period following exposure to a primary case .

PREVALENCE
● It is defined as all current cases (old and new) existing at a given point in
time or over a period of time in a given population.
● Total number of all individuals who have an disease at a particular time or
period divided by the population at risk of having the disease at this point
in time or midway through the period
● TYPES OF PREVALENCE
● 1) Point prevalence
. 2) Period prevalence

RELATIONSHIP BETWEEN PREVALENCE
AND INCIDENCE
● Prevalence = Incidence × Duration

References -
● PARK’S TEXTBOOK OF PREVENTIVE AND SOCIAL
MEDICINE
● https://en.m.wikipedia.org/wiki/John_Snow

PSM PRESENTATION TOOLS of Measurement Corrected 2.pptx

PSM PRESENTATION TOOLS of Measurement Corrected 2.pptx

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