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Introduction To Health
Statistics
Dr. Premananda Bharati
Professor and Head
Biological Anthropology Unit
Indian Statistical Institute
203, B.T. Road, Kolkata – 700 108
West Bengal, India
E-mail: [email protected]
1
What is health statistics?
Health and medical statistics incorporate a variety of data
types. The most common statistics reported are vital (birth,
death, marriage, divorce rates), morbidity (incidence of disease
in a population) and mortality (the number of people who die of
a certain disease). Other common statistical data reported are
health care costs, the demographic distribution of disease based
on geographic, ethnic, and gender variables, and data on the
socioeconomic
status
and
education
of
health
care
professionals.
2
CLASSIFYING DISEASES
• Acute Diseases
– Acute diseases are those conditions in which the peak
severity of symptoms occurs within three months (usually
sooner), and recovery in those who survive is usually
complete.
• Chronic Diseases
– Chronic diseases are those in which symptoms continue
longer than three months and in some cases for the
remainder of the person’s life. Recovery is slow and
sometimes incomplete.
3
CLASSIFYING DISEASES (cont’d.)
• Communicable (Infectious) Diseases
– Diseases for which biological agents or their products are the cause and
which are transmissible from one individual to another.
– The disease process begins when the causative agent is able to lodge and
grow or reproduce within the body.
– The process of lodgment and growth of a microorganism or virus in the
host is termed infection.
• Non-communicable (Noninfectious) Diseases/Illnessses
– Those diseases or illnesses that cannot be transmitted from an infected
person to a susceptible, healthy one.
– Several, or even many, factors may contribute to the development of a
given non-communicable health condition.
– The contributing factors may be genetic, environmental, or behavioral in
nature.
4
Classification of Diseases
• Acute Diseases
– Communicable
– Non-communicable
(incl. trauma)
Common cold, pneumonia, mumps,
measles, typhoid fever, flu.
Appendicitis, poisoning, trauma (e.g.,
due to automobile accidence, fires,
etc.)
• Chronic Diseases
– Communicable
– Non-communicable
Tuberculosis, AIDS, syphilis, rheumatic
fever following streptococcal infections,
herpes
Diabetes, coronary heart disease,
osteoarthritis, cirrhosis of the liver due
to alcoholism, hypertension.
5
COURSE OF INFECTIOUS DISEASE
• Exposure/Invasion of Host
• Incubation -- period of time between exposure and onset of
symptoms -- e.g., interval between HIV infection and
development of AIDS can be as long as 10-15 years
• Host reaction
• Disease runs course -- treatment, recovery/death (most
people don’t die from infectious diseases)
MODES OF COMMUNICABLE DISEASE TRANSMISSION
 Direct Transmission
 Indirect Transmission
6
DIRECT TRANSMISSION
 Immediate transfer of the disease agent by direct contact
between the infected and the susceptible individuals
 Occurs through such acts as touching, biting, kissing, sexual
intercourse, or by direct projection (droplet spread) by
coughing or sneezing within a distance of one meter
 Examples of diseases for which transmission is usually direct
are AIDS, syphilis, gonorrhea, and the common cold
7
INDIRECT TRANSMISSION
May be one of three types: Air-borne
 Vehicle-borne(toys,handkerchiefs,
food, bleeding)
 vector-borne (living organism, fly,
mosquito)
8
Infectious Diseases
9
Factors Influencing Disease Transmission
Agent
Environment
• Weather
• Infectivity
• Housing
• Pathogenicity
• Geography
• Virulence
• Occupational setting
• Immunogenicity
• Air quality
• Antigenic stability
• Food
• Survival
• Age
• Sex
Host
• Genotype
• Behaviour
• Nutritional status
• Health status
10
Leading Causes of Mortality and Burden of Disease
World , 2004
Mortality
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Ischaemic heart disease
Cerebrovascular disease
Lower respiratory infections
COPD (Chronic obstructive pulmonary disease)
Diarrhoeal diseases
HIV/AIDS
Tuberculosis
Trachea, bronchus, lung cancers
Road traffic accidents
Prematurity, low birth weight
DALYs*
%
12.2
9.7
7.1
5.1
3.7
3.5
2.5
2.3
2.2
2.0
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Lower respiratory infections
Diarrhoeal diseases
Depression
Ischaemic heart disease
HIV/AIDS
Cerebrovascular disease
Prematurity, low birth weight
Birth asphyxia, birth trauma
Road traffic accidents
Neonatal infections and other
%
6.2
4.8
4.3
4.1
3.8
3.1
2.9
2.7
2.7
2.7
(*DALY) The disability-adjusted life year is a measure of overall disease burden, expressed as the number of
years lost due to ill-health, disability or early death.
11
Distribution of child deaths for selected causes by selected
WHO region, 2004
12
Adult mortality rates by major cause group and region, 2004
Cardiovascular diseases
High income
Cancers
Other noncommunicable diseases
Western Pacific
Injuries
HIVAIDS
Americas
Other infectious and parasitic diseases
Maternal and nutritional conditions
Eastern Mediterranean
South East Asia
Europe
Africa
0
2
4
6
8
10
Death rate per 1000 adults aged 15–59 years
12
13
Global projections for selected causes,
2004 to 2030
12
Cancers
Deaths (millions)
10
Ischaemic HD
Stroke
8
6
Acute respiratory
infections
4
Road traffic
accidents
Perinatal
HIV/AIDS
TB
Malaria
2
0
2000
2005
2010
2015
2020
2025
2030
Updated from Mathers and Loncar, PLoS Medicine, 2006
Projected deaths by cause and income, 2004 to 2030
30
Intentional injuries
Other unintentional
Road traffic accidents
Deaths (millions)
25
Other NCD
20
Cancers
15
CVD
10
Mat//peri/nutritional
5
Other infectious
HIV, TB, malaria
0
2004
2015
2030
High income
2004
2015
2030
Middle income
2004
2015
2030
Low income
15
What is public health?
Public Health is the science of
protecting
and
improving
the
community health through health
education, promotion of healthy
lifestyles, research, and disease
prevention strategies.
16
Public health components





MULTIDISCIPLINARY SCIENCES
CONCEPTS
SKILLS
PRACTICES
ALL INTERTWINED WITH BELIEFS
17
Associated disciplines-I
•Preventive medicine:
(.. The application of preventive measures by
clinical practitioners…)
•Community medicine:
(..the study of health and disease in the
population of a defined community..)
18
Associated disciplines-II











Epidemiology
Statistics
Nutrition
Health education (debatable if separate or part of PH)
Environmental health
Population and demography
Medical sociology
Anthropology
Health ethics
Behavioral sciences/health education
Health services administration
19
Again, what is public health?
 Public health clearly includes some elements
of medical practice, preventive medicine,
community medicine. It also includes other
disciplines such as nutrition, environmental
health, and anthropology.
 However, it is greater than the sum
of all theses parts.
20
Areas of concentration
• Health promotion:
(...the process of enabling people to increase
control over and improve their health...)
• Disease prevention:
(...the goals of medicine are embodied in the
word prevention: to promote health, to preserve
health, to restore health when it is impaired, and
to minimize suffering and distress)
21
Public health v. medicine
Patient
Population
Individual
Intervention Assessment, Policy Medical, surgical
Process
Outcome
Development,
Assurance
treatment
System
management
Patient
management
Healthy
community
Healing
22
Agencies concerned with public health?


Practice settings
 Govt. agencies-MOH
 Local agencies, municipalities ..etc
 NGOS
 Private
 International organizations?
Academic institutions
 Schools of public health & other programs
23
Core Functions



Assessment
Policy Development
Assurance
Vision

Healthy People in Healthy Communities
Mission
Promote physical and mental health and prevent
disease, injury, and disability.

24
The fundamental obligation of agencies
responsible for population-based health is to:






Prevent epidemics and the spread of disease
Protect against environmental hazards
Prevent injuries
Promote and encourage healthy behaviors and
mental health
Respond to disasters and assist communities in
recovery
Assure the quality and accessibility of health
services
25
Core Functions
26
The measures
• Measures of disease occurrence
– Prevalence
P
– Risk
R
– Incidence rate
I
• Measures of causal effects
– Risk difference
RD
– Risk ratio
RR
– Incidence rate difference
IRD
– Incidence rate ratio
IRR
– Odds ratio
OR
27
Measures of disease occurence
• Prevalence P
• Risk CI
• CFR = risk of death
• Incidence rate I
– Mortality M = incidence of death
28
Prevalence
(Prevalence proportion)
The proportion of a population with a certain disease at a given point in time
The probability that a randomly chosen individual has the disease
P=
number of diseased people at the point in time
number of individuals in the population
P = 0 to 1, or percentage, per million etc.
Prevalence : Prevalence is an indicator of the disease occurring in a population. A
prevalence rate refers to the proportion of cases of a disease existing in a population,
which includes freshly diagnosed cases as well as those living with the disease, to
the total population. Thus,
Prevalence Rate = No. of cases of a disease / Population size.
It is good measure of the burden of a disease in a society or a population.
If diabetes is taken into consideration in a population of 50,000 people out of whom
2000 are freshly diagnosed cases whereas 5000 are already living with diabetes,
then the prevalence of diabetes will be 0.14 (7000/50000) or 14% or 14000 per
100,000 persons.
29
Point prevalence is prevalence at a certain point in time, the true
prevalence. The point is either a calendar point in time, or
a certain event, such as birth.
Lifetime prevalence is the proportion who has had the
characteristic (the disease) during their lifetime.
Seroprevalence is the proportion who has antibodies, marking
earlier or current infection, i.e. a lifetime prevalence of the
infection.
30
Calculating prevalence
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1
A
B
C
D
E
F
P = 2 / 4 = 0.5 = 50%
31
Risk (R)
(Incidence proportion, cumulative incidence, attack rate)
The proportion of the population who gets the disease during a
given time period
The risk that a randomly chosen individual will get the disease
during the time period
R = number of new cases during the time period
number of individuals in the population
R = 0 to 1, or percent, per million etc., but the period must be
stated
32
Incidence rate
• Incidence rate is the number of new cases of a disease reported
for a given population in a given time period. It refers to the
fraction of a population that develops a disease in a given time
or the number of new cases reported for contacting a disease or
a condition during a given time period. Incidence is thus an
indicator of the risk of developing some new disease or
condition within a specified period of time.
• The incidence and prevalence are not same and represent very
different concepts. Incidence is the rate at which people
contract a disease whereas prevalence represents the total
number of diseased people in a population at any given time.
Prevalence and incidence are demonstrated with the help of the
following example
33
• Example: Let us imagine a sample population of 1000 individuals in
whom we want to assess the incidence rate of developing diabetes
over a period of 10 years. The individuals were followed up at three
cut points of time; at the start, after 5 years and at the end of 10
years.
• At the start of the study (time, t=0), there were already 100
individuals who had diabetes.
• A follow up for 5 years (time, t=5) revealed that 70 more persons
have contracted the disease during this period.
• At the end of ten years (time, t=10), 80 more individuals have
contracted the disease.
• So, at the end of the study after 10 years, the total number of
diabetes patients in a sample population of 1000 has been 100 + 70 +
80 = 250 cases.
• Therefore, prevalence of diabetes in this sample population =
250/1000 or 0.25 or 25%.
34
Calculating risk
Admission day
7 days later
A
B
x
C
x
D
E
Condition: Same follow up for all
R = 2 / 5 = 0.4 = 40%
35
Attack rate (AR)
• Risk during an outbreak
Usually expressed for the entire epidemic period,
from the first to the last case
Ex:
Outbreak of
in March 1999
cholera
in
country
X
– Number of cases = 490
– Population at risk = 18,600
– Attack rate = 2.6%
36
Incidence rate (I)
(incidence density)
The speed of new cases of a disease in the population
I=
number of new cases in the time period
sum of risk period for all individuals
I = number per time unit of risk, e.g. per person year
37
Incidence rate (I)
The numerator is the number of new cases in a time period
The denominator is person time at risk
-
either the size of the population in the middle of the
period (usually acceptable)
-
or the sum of the calculated time at risk for all the persons
in the population
38
Calculating incidence rate
16 17 18 19 20 21 22 23 24 25 26
Days at risk
6.0
A
B
x
6.0
10.0
C
x
D
8.5
E
5.0
Total days at risk
35.5
I = 2 / 35.5 persondays = 0.56 / 100 persondays
39
Mortality rate (M)
The speed of new deaths caused by this disease in the population,
i.e. the incidence of death
M = number of new deaths of the disease in the period
sum of risk period for all individuals
M = number per time unit of risk, e.g. per person year
40
Risk versus incidence rate
Risk (R)
Incidence rate (I)
Synonyms
(incidence proportion,
cumulative incidence,
attack rate)
(incidence density)
Smallest
value
Greatest
value
0 (or 0%)
0
1 (or 100%)
∞
Units
None
/ person-time
Why do we need measures of population health?
Governments wish to monitor health of citizens
–
–
–
–
–
–
–
To set priorities for health services & policies
To evaluate social and health policies
To compare health of different regions
To identify pressing health needs
To draw attention to inequalities in health
Highlight balance between length and quality of life
Numerical index desirable: a “GNP of Health”
42
Classifying Population Health Measures by
their Purpose
1. Descriptive measures:
i. Current health status (e.g., health surveys)
ii. Evaluative measures (e.g., to assess outcomes of
health policies)
2. Analytic measures include an implicit time
dimension:
iii. Predictive methods (risk assessment; projections
of disease burden) look forward;
iv. Explanatory measures (income inequality or social
cohesion) look backwards.
43
These purposes may correspond to different
types of research
Descriptive
(measures of
current health status)
Health
Services
Research
Evidence-based
policy
Evaluative
(process & outcome
measures)
Evidence-based
medicine
Predictive
(projection &
risk estimation)
Etiologic
epidemiology
Analytic
(etiology & determinants)
44
Classifying Population Health Measures by
their Focus
1. Aggregate measures combine data from individual people,
summarized at regional or national levels. E.g., rates of smoking or
lung cancer.
2. Environmental indicators record physical or social characteristics of
the place in which people live and cover factors external to the
individual, such as air or water quality, or the number of
community associations that exist in a neighborhood. These can
have analogues at the individual level.
3. Global indicators have no obvious analogue at the individual level.
Examples include contextual indicators such as the existence of
healthy public policy; laws restricting smoking in public places, or
social equity in access to care; social cohesion, etc.
Morgenstern H. Ecologic studies in epidemiology: concepts, principles, and methods. Annual Reviews of Public Health 1995;
16:61-81.
45
Linking the focus of a measure to its application
• Aggregate measures are typically used in descriptive studies;
they focus on the individuals within the population, i.e.
idiographic. They measure health in the population
• Environmental measures can be used in descriptive, analytic
or explanatory studies
• Global measures mainly used in analytic studies; focus on
generating theory (nomothetic studies). They could measure
health of the population
46
Aggregate Measures:
Mortality-Based Indicators
Life expectancy
47
Life Expectancy
Life expectancy is the expected (in the
statistical sense) number of years of life
remaining at a given age.
48
Expectancies and Gaps
100%
G
80%
60%
40%
E
20%
0%
0 10 20 30 40 50 60 70 80 90 100
• From a typical survival curve,
we can either consider the
life expectancy (“E”), or the
gap (“G”) between current
life expectancy and some
ideal.
• Expectancies are generic;
gaps can be disease-specific
(e.g., life yrs lost due to
cancer)
49
Aggregate Measures that
Combine Mortality & Morbidity
Health expectancies
Health gaps
50
Composite Measures
• Aim to represent overall health of a population
• Composite measures combine morbidity and
mortality into a health index. (An index is a numerical
summary of several indicators of health)
• Mortality data typically derived from life tables;
morbidity indicators from health surveys, e.g.
• Self-rated health
• Disability or activity limitations
• A generic health index
51
Sidebar: Different Types of Morbidity Scales for
Use in Composite Measures
• Generic instruments cover a wide range of health
topics, e.g. reflecting the WHO definition. These can
be health profiles (e.g., Sickness Impact Profile, SF36) or “health indexes” (e.g., Health Utilities Index,
EuroQol)
• Specific instruments
– Disease-specific (e.g., Arthritis Impact Measurement Scale)
– Age-specific (e.g., Child Behavior Checklist)
– Gender-specific (e.g., Women’s Health Questionnaire)
52
Measures of Mortality
Mortality Rates
Infant Mortality Rate
Neonatal Mortality Rate
Postneonatal Mortality rate
Perinatal Mortality Rate
Fetal Mortality Rate
Maternal Mortality Rate
Death Rates
Crude Death Rate
Age-Specific Death Rate
Cause-Specific Death Rate
Age-Adjusted Death Rate
53
Chart of Early Life Mortality Measures
54
Use of Health Statistics
 to describe the level of community health
 to diagnose community ill
 to discover solutions to health problems and find clues
for administration action
 to determine priorities for health programme
 to maintain control during execution of programme
 to develop procedures, classification, definitions and
techniques such as recording systems, sampling
schemes. etc.
55
Use of Health Statistics
 to promote health legislation
 to determine the met and unmet health
needs
 to create administrative standards of health
activities
 to determine success or failure of specific
health programmes or undertake overall
evaluation of public health work
 To demand public support for health work
56
Usefulness of health statistics
• How many people suffer from particular diseases, how
often and for how long
• How fatal the different diseases are
• To what extent people are prevented by these diseases
from carrying on their normal activities
• To what extent disease are concentrated in particular
groups of the population, eg., according to age, sex,
ethnic group, occupation or place of residence
57
Usefulness of health statistics
• How far the above factors vary from time to
time (variation according to season or from
year to year
• What is the effect of medical care and health
services on the control of disease incidence.
58
59