concept of rate, ratio and proportion

1. TOOLS OF MEASUREMENT
1) Rate 2)Ratio & 3)Proportion
ØRATE – Measures the occurrence of some
particular event in a population during a given
time period.
ØComprises of
Ø*Numerator *Denominator
*Time specification & *Multiplier
ØTypes- Crude rates –CBR, CDR
Specific rates
Standardized rates

2. • It Signifies speed or the frequency of
occurrence per unit time.
• The numerator is a part of the denominator.
• Eg. Notification rate of new sputum smear +ve
cases = New ss +ve / 100,000 population
• Cure rate :No. of cases cured x100
No. Of cases under Trt.

3. RATIO :
• Relation of size between two random
quantities.
• The numerator is not a component of
denominator.
• e.g. Sex ratio, doctor-population ratio, child-
women ratio.

4. PROPORTION
• Is a ratio which indicates the relation in
magnitude of a part of the whole.
• Numerator is always included in denominator.
• Usually expressed as %ge.
• Measurement of the size of a part out of the
whole, usually the whole taken as 100. If the
fraction is too small, the base can be 1000 or any
10x.

5. CONCEPT OF NUMERATOR & DENOMINATOR
ØNUMERATOR- refers to the no. of times an
event has occurred in a population during a
specified time period.
ØDENOMINATOR –It may be
Related to population- Mid year population
Population at risk, Person-time, Person-distance,
Subgroups of the population
Related to total events- IMR, CFR

6. ØHealth can not be defined in exact
measurable terms. Health changes can
only be reflected by indicators.
ØIndicators are defined as variables which
help to measure health changes.

7. OBJECTIVES OF MEASUREMENT
ØTo know health status of a community.
ØTo compare between diff. countries.
ØFor assessment of health care needs.
ØFor allocation of scarce resources.
ØFor monitoring & evaluation of health
services, activities & programmes.
ØPlanners can know the objectives &targets
of a Programme are being attained.
ØTo fix up priorities in adoption of future
health measures.

8. Characteristics of an indicator
An ideal indicator should be
ØValid –measures what supposed to measure
ØPrecise/reliable –same results if used by
different individuals in similar circumstances.
ØSensitive- reflect small changes in health status.
ØSpecific- only in the situation concerned.
ØFeasible- ability to obtain data needed.
ØRelevant- Contribute to the phenomenon of
interest.

9. TYPES OF INDICATORS
ØMortality indicators
ØMorbidity indicators
ØDisability rates
ØFertility indicators
ØNutritional status indicators
ØHealth care delivery indicators
ØUtilization rates

10. Cont.
ØIndicators of social & mental health
ØEnvironmental indicators
ØSocio-economic indicators
ØHealth policy indicators
ØIndicators of quality of life
ØOther indicators

11. MORTALITY INDICATORS
CRUDE DEATH RATE-
No of deaths during the year 1000
Mid year population
• Decrease in CDR provides a good tool for
assessing the overall health improvement in
a population.
• They lack the comparability for communities
or national or international level b/c they
differ by age, sex, race etc.

12. SPECIFIC DEATH RATES
• Cause or disease specific- TB, cancer,
accident -Computed for total population
-Calculated per 100,000
-Makes easier for comparison bet. diff.
causes
• Related to specific groups- Age, sex, both
No of deaths in specified age group 1000
Mid yr. population of same age group
-Can help us to identify particular groups or
groups at risk for preventable action.

13. • STILL BIRTH RATE=
Fetal deaths weighing over 500g. 1000
Total live +still births over 500g. at birth
• PERINATAL MORTALITY RATE=
Late fetal +Early neonatal deaths 1000
Live births in same year
-gives good indication of the extent of
pregnancy wastage, quality & quantity of
maternity care available to mother
&newborn.
• -reflects the results of maternity care.

14. NEONATAL MORTALITY RATE
• No. of deaths of children under
28 days of age in a yr. 1000
Total live births in the same year
-Measures the intensity with which endo-
genous factors (e.g. LBW, Birth injuries)
affect infant life.
-High NMR with endogenous causes
suggest to improve antenatal & postnatal
services to expectant mothers.

15. POSTNEONATAL MORTALITY RATE
• No. of deaths of children between
28 days & 1 yr. of age in a given yr. 1000
Total no. of live births in the same yr. -
Dominated by exogenous causes.
• INFANT MORTALITY RATE
No. of deaths of children less than 1000
1 yr. age in a year
No. of live births in the same yr.
-Most sensitive indicator of health status &
SE conditions of the population.

16. CHILD DEATH RATE
• No. of deaths of children aged
1-4 yrs. during a given year 1000
Total no. of children aged 1-4 yrs.
at the middle of year
-It is the more refined indicator of the social
situation in a country. -
If more, it reflects the inadequate MCH
services, insufficient nutrition, low
immuniza- tion coverage &adverse env.
exposure etc.

17. UNDER -5 MORTALITY RATE
• No. of deaths of children less than
5 yrs. of age in a given year 1000
No. of live births in the same yr. -
UNICEF considers it as the best single
indicator of social development&wellbeing.
MATERNAL MORTALITY RATE Total no.
of maternal deaths in an
area during a given yr. 1000
Total no. of live births in same area & yr.
-Fine measure of quality of maternity
service.

18. SEX SPECIFIC DEATH RATE
• MALE DEATH RATE =
Male deaths in a year 1000
Mid year population of males -
For comparison.
AGE-SEX SPECIFIC DEATH RATE
• Death rate of women in reproductive age gr.
= Female deaths in age gr. 15-49 1000
Female population of age gr. 15-49

19. CASE FATALITY RATE
• Total no. of deaths due to a
particular disease 100
Total no. of cases due to same disease
-Time interval is not specified.
-Represents the killing power of a disease.
-Used in acute infectious disease.
-Closely related to virulence.
-Important while investigating an
epidemic.

20. PROPORTIONAL MORTALITY RATE
• Expresses the no. of deaths due to a particular
cause (or in a specified age group) per 100 or
1000 total deaths.
• a) Proportional mortality from specific disease
• b) Under 5 proportional mortality rate
• c) Proportional mortality rate for aged 50 years
or above
• Useful indicators within any population group
of the relative importance of specific disease or
dis. group as a cause of death.

21. SURVIVAL RATE
• Total no. of patients alive after a period * 100
Total no. of patients diagnosed or treated
-Can be used for assessment of standards of therapy.
STANDARDISED DEATH RATES - for the purpose
of comparison between different populations.
1) Direct standardization
2) Indirect standardization-
a) Standardized mortality ratio (SMR)-
observed deaths * 100
expected deaths
a) By index rates
b) Life table –age adjusted summary of current all-
causes mortality.

22. MEASUREMENT OF MORBIDITY
• Any departure subjective or objective
from a state of physiological well being.

23. INCIDENCE
• No. of new cases of specific disease
during a specified time interval * 1000
Population at risk during that period
• Attack rate
• Secondary attack rate
– Restricted to acute diseases.
– Is a health status indicator. Useful for taking steps
for prevention & treatment.

24. Attack rate
Attack rate =
No. of persons exposed to F who got ill *100
Total no. of persons exposed to F
AR = iE / NE
Need for
denominator
(all exposed)
Secondary Attack rate
Defined as the number of exposed persons developing the
disease within the range of incubation period following
exposure to a primary case.

25. Incidence may change genuinely (increase or
decrease) with the following factors:
• Introduction of a new risk factor (e.g., contraceptive
and increase in Thromboembolism, food additives and
cancer);
• Changing habits.
• Changing virulence of causative organisms.
• Changing potency of treatment or intervention
programmes.
• Selective migration of susceptible persons to an
endemic area, which increase the incidence of the
disease.

26. PREVALENCE
• Refers to all current cases ( old & new) existing at a given point
or period of time in a given population.
• Prevalence =
All current cases existing at a given point or period of time * 100
Population at risk
• May be
-Point prevalence
-Period prevalence
• Uses -1)Helps to estimate the magnitude of disease & identify
high risk population.
2)Useful for administrative & planning purposes.

27. These rates are typically obtained from cross –sectional studies;
occasionally, they are based on registersof specific disease.
Prevalencedepends on two main factors:
- previous incidence ,and
- Duration or chronicity of disease.
When both incidence and during of a specific disease are
relatively stable,
Prevalence(P) = incidence (I) X duration (D)

28. Prevalence may change over time in response to:
• Changes in incidence,
• Changes in disease duration and chronicity (e.g., some
disease may become shorter in duration or more acute
because of high recovery rate or high case fatality rate),
• Intervention (preventive) programmes,
• Selective attrition (e.g., selective migration of cases,or of
susceptible or immune persons ), and
• Changing classification of what constitutes an “active ” case
and whether an “ arrested”case is counted or not.

29. Results of Screening for diabetes on incidence rate
5 died
5 migrated
5 recovered
25 cases
40 cases
960 free
20 cases
940 free
1000
women
Screening
1 January
1 January
2012
31 December
2012
Incident cases
during 2012
Prevalent cases
on 31 December
Attrition

30. Duration of illness
• 1)Days of illness per exposed person
• 2)Days per illness per ill per person
• 3)Days of illness per spell
Other morbidity indicators
• Notification rates
• Attendance rates at OPDs, health centre etc.
• Admission, readmission & discharge rates

31. DISABILITY RATES
• Event type indicators -
-No. of days of restricted activity
-Bed disability days
-Work loss days within a specified period.
• Person type indicators-
-Limitation of mobility
-Limitation of activity
• Health adjusted life expectancy (HALE)
• Disability adjusted life year (DALY)

32. • HALE (Health-Adjusted life expectancy) – The
equivalent number of years in full health that a
newborn can expect to live based on current rates
of ill-health and mortality.
• QALY (Quality adjusted life years) – measure of
disease burden both the quality and quantity of life
lived. It is used in assessing the value for money of
a medical intervention.
• DFLE (Disability free life expectancy) – Av. No. of
years an individual is expected to live free of
disability.
• DALY (Disability adjusted life years) –measure of
overall disease burden, expressed as a no. of years
lost due to ill-health, disability or early death.

33. FERTILITY INDICATORS
• Crude birth rate
• Fertility rates-
General fertility rate
Age specific fertility rate
Total fertility rate
• Reproduction rate-
Gross reproduction rate
Net reproduction rate
• Sex ratio at birth
• Pregnancy rate
• Abortion rate

34. NUTRITIONAL STATUS INDICATORS
• Anthropometric measurements of
preschool children e.g. weight, height,
mid- arm circumference
• Heights (sometimes weights) of children
at school entry
• Prevalence of low birth weight (<2.5 kg.)

35. HEALTH CARE DELIVERY INDICATORS
• Doctor population ratio
• Doctor –nurse ratio
• Population – bed ratio
• Population per Health / sub centre
• Population per T.B.A.
-These reflect the equity of distribution of
health resources in diff. parts of country &
of the provision of health care.

36. UTILIZATION RATES
• Utilization of services – or actual coverage- is
expressed as the proportion of people in need of
a service who actually receive it in a given period.
• E.g.Proportion of infants fully immunized.
Pregnant women who receive ANCs.
%ge of population using various methods of
family planning
Bed occupancy rate
Average length of stay

37. INDICATORS OF SOCIAL & MENTAL HEALTH
• Suicide, homicide & other violence &crime
• Road traffic accidents
• Juvenile delinquency
• Alcohol & drug abuse, smoking
• Obesity
• Family violence, battered baby & battered
wife syndromes

38. ENVIRONMENTAL INDICATORS
Reflect the quality of physical & biological
env. in which diseases occur & people live.
These indicators are relating to
• Pollution of air & water
• Radiation, Noise
• Solid wastes
• Exposure to toxic sub.s in food & drink
Most useful- proportion of population
having assess to safe water & sanitation
facilities.

39. SOCIO-ECONOMIC INDICATORS
• Rate of population increase
• Per capita GNP
• Level of unemployment
• Dependency ratio
• Literacy rates (esp. Female literacy rate)
• Family size
• Housing, the no. of living room
• Per capita calorie availability

40. HEALTH POLICY INDICATORS
• Indicators of political commitment for
allocation of adequate resources.
-Proportion of GNP spent on health
services
-Proportion of GNP spent on health
related activities
-Proportion of total health resources
devoted to primary health care

41. INDICATORS OF QUALITY OF LIFE
• PQLI- Most important & composite
health indicator.
• It includes
-Infant mortality
-Life expectancy at age one
-Literacy

42. OTHER INDICATORS
• Social indicators-
Population, Family formation, Learning &
educational services, Earning activities,
Social security & welfare services etc.
• Basic needs indicators- used by ILO
Calorie consumption, assess to water, life
expectancy, deaths due to disease,
illiteracy, doctors & nurses per
population, rooms per person, GNP per
capita

43. Health for all indicators
By WHO. Four categories
• 1) Health policy indicators-
-Political commitment to health for all
-Resource allocation
-the degree of equity of distribution of
health services
-Community involvement
-Organizational framework &
managerial process

44. Social & economic indicators related to health
- Rate of population increase
- GNP or GDP
-Income distribution
-Work conditions -
Adult literacy rate
-Housing -Food availability
Indicators for the provision of health care
- Availability -accessibility
-Utilization -Quality of care

45. Health status indicators
• LBW
• Nutritional status & psychosocial dev. of
children
• IMR ,Child mortality rate( 1-4 yrs.)
• Life expectancy at birth , MMR
• Disease specific mortality
• Morbidity- incidence, prevalence
• Disability prevalence

46. USES OF EPIDEMIOLOGY
• To study historically the rise and fall of disease in
the population – history of diseases
• Community diagnosis – identification and
quantification of health problems in a community
in terms of mortality and morbidity rates and
ratios, and identification of their correlates for the
purpose of defining those individuals or groups at
risk or those in need of health care.
• Planning and evaluation – Planning is essential for
rational allocation of limited resources. Evaluation
is to know whether the measures undertaken are
effective or not in reducing the frequency of
disease or health problems.

47. • Evaluation of individual’s risks and chances –
degree of risk in a population. Eg. Risk of lung
ca in smokers and nonsmokers.
• To identify syndromes
• Completing the natural history of disease –
entire spectrum of the disease
• Searching for causes and risk factors – to
identify causes and risk factors for a disease
• To forecast future disease trends