Briefly describing: (1.) Crude Death Rate (2.) Specific Death Rate (3.) Proportional Mortality Rate (4.) Maternal Mortality Ratio (MMR) (5.) Odds Ratio (6.) Standardized Mortality Ratio (SMR) (7.) Case Fatality Rate (CFR)

1. Rates & Ratios
Dr. Madhav Mehta (madhavmehta013@gmail.com)

2. CRUDE DEATH RATE
• Definition: ‘The number of deaths per 1000 estimated mid year population
in one year, in a given place’.
(It measures the rate at which deaths are occurring from various causes
in a given population, during a specified period.)
Formula:
(Slide 02)

3. Crude death rate summarizes the effect of 2 factors :-
(a.) Population composition
(b.) Age specific death rates
Table:
(Slide 03)

4. Disadvantage:
• They lack comparability for communities with
populations that differ by age, sex, race, etc.
• Crude death rate should always be examined first
and later the age specific death rate which are most
useful single measures of mortality.
(Slide 04)

5. • Definition: ‘The cause specific mortality rate is mortality rate from a specified
cause for a population’.
• Numerator is the number of deaths attributed to a specific cause.
• Denominator remains size of population.
• It may be;
(a.) Caused or disease specific: TB, Cancer, Accident
(b.) Related to specific group: Age specific, Sex specific, Age & Sex specific,etc.
It can help us to identify particular groups or groups 'at risk', for preventive action.
SPECIFIC DEATH RATE
(Slide 05)

6. (Slide 06)

7. • It express the
number of deaths
due to a particular
cause per 100/1000
total deaths
PROPORTIONAL MORTALITY RATE
(Slide 07)

8. • Proportional rates are used when population data are not available.
• It is usually computed for broad disease group.
• The prevailing cause of death vary according to age and sex, it is desirable to
compute proportionate mortality separately for each age and sex group in
order to determine measures directed to particular age-sex groups for the
reduction of preventable mortality.
(Slide 08)

9. • It expresses a relation in size between 2 random quantities.
• The numerator is not a component of denominator.
• It is expressed in form of X:Y or X/Y
• Example: The ratio of white blood cells relative to red cells is 1:1600, meaning that
for each white cell there are 600 red blood cells.
• Other examples include Sex Ratio, Doctor-population Ratio, Child-Woman ratio, etc.
RATIOS
(Slide 09)

10. • Given by:
MATERNAL MORTALITY RATIO
• In India MMR is 113 per lakh live births.
• Highest in Assam - 215
• Lowest in Kerala - 43
(Slide 10)

11. Categories of ratio:
Risk ratio: ‘The ratio of the probability of an outcome in an exposed group to the
probability of an outcome in an unexposed group.’
• Expressed as: Ie/Iu
• Assuming the causal effect between the exposure and the outcome, values of RR can be
interpreted as follows:
(1.) RR = 1 means that exposure does not affect the outcome.
(2.) RR < 1 means that the risk of the outcome is decreased by the exposure.
(3.) RR > 1 means that the risk of the outcome is increased by the exposure.
(Slide 11)

12. The group exposed to
treatment (left) has half
the risk (RR = 4/8 = 0.5)
of an adverse outcome
(black) compared to the
unexposed group (right).
(Slide 12)

13. • Definition: An odd ratio Is the odds of event in 1 group.
• Example: Those exposed to the drug divided by the odds of the event in another
group not exposed.
• In case control study since incidence is not available, So relative risk cannot be
calculated directly.
• Therefore odd ratio is obtained, which is a measure of Strength of association
between exposure and outcome.
ODDS RATIO
(Slide 13)

14. (Slide 14)

15. • Simplest & Most Useful form of indirect standardisation.
• SMR is defined as a ‘Ratio of 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’.
• In other words SMR compares the mortality in a study group with the mortality that this study
group would have had if they had experienced national mortality rates.
STANDARDIZED MORTALITY RATIO
(Slide 15)

16. (Slide 16)
If the ratio has value > 100, then the study group appears to carry a
greater mortality risk than that of whole population if the ratio has
value < 100, then mortality in study group would seem
to be proportionately less then whole population.

17. • Definition: ‘It is a ratio which indicates the relation in
magnitude of a part of the whole’.
• Numerator is a part of the Denominator.
• Multiplier is 100 (as we expressed in percentage)
• Proportion is calculated at one point of time.
• Example: (a.) CFR & (b.) Prevalence
PROPORTION
(Slide 17)

18. • Means Case Fatality Rate (*rate is a misnomer here)
• It’s a proportion of deaths in a given disease
• Example:
• Left out of 300 cases, 90 died. Therefore CFR is 30%
CFR
(Slide 18)

19. •Tells severity of disease.
•Tells killing power of a disease.
•Gives virulence of the agent.
Uses:
(Slide 19)

20. Thank You!
Dr. Madhav Mehta (madhavmehta013@gmail.com)