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1. Specific measures of disease
• There are a variety of specific measures of
disease used in epidemiology that are important
to know
• Note: many of these measures are called “rates”
but not all of these are true rates
– See if you can determine which are rates and which
are proportions or ratios

2. Specific measures of disease
• Neonatal mortality rate
• Index of the risk of death in the first 28 days of
life
– Numerator: the number of deaths during one calendar
year of children <28 days old
– Denominator: the number of live births during the
same calendar year
– Usually expressed per 1,000
– Example: in the US in 2007 the neonatal mortality rate
was 4.4 deaths / 1,000 live births

3. Specific measures of disease
• Postneonatal mortality rate
• Index of the risk of deaths in infants aged 28 days – 1 year
– Numerator: the number of deaths in children aged 28 days – 1 year
calendar year
– Denominator: the number of live births during that calendar year
– Usually expressed per 1,000
– NOTE: will all infants who die in a calendar year have been born in t
same calendar year?
– Example: in the US in 2007 the postneonatal mortality rate was 2.3
deaths / 1,000 live births

4. Specific measures of disease
• Infant mortality rate
• Index of the risk of deaths in infants up to 1 year
• Sum of neonatal and postneonatal mortality
rates
– Numerator: the number of deaths in children up to 1
year of age in a calendar year
– Denominator: the number of live births during that
calendar year
– Usually expressed per 1,000
– Example: in the US in 2007 the infant mortality rate
was 6.75 deaths / 1,000 live births

5. Specific measures of disease
• Infant mortality rate in the US in 2007 by cause
– Congenital anomalies 1.3/1,000
– Short gestation, low birth weight 1.1/1,000
– SIDS 0.5/1,000
– Maternal complications of pregnancy 0.4/1,000
– Note: cause specific often presented per 100,000 live
births

6. Specific measures of disease
• Maternal mortality rate
– Numerator: the number of deaths in a year from
puerperal causes (pregnancy complications,
childbirth, puerperium (time after the birth))
– Denominator: the number of live births during that
same year
– NOTE: denominator is all live births and not all
pregnancies because there is no surveillance system
for pregnancies
– Usually expressed as per 100,000
• Example:
– US 1960: 37.1 maternal deaths / 100,000 live births
– US 1990: 8.3 maternal deaths / 100,000 live births

7. Specific measures of disease
• Crude birth rate
– Numerator: the number of live births during a given
time interval
– Denominator: estimated total population at mid-
interval
– Usually expressed per 1,000
– Example: (next slide)

8. Specific measures of disease

9. Specific measures of disease
• General fertility rate
– Numerator: the number of live births during a given
time interval
– Denominator: estimated number of women aged 15-
44 years (sometimes 15-49) at mid-interval
– Usually expressed per 1,000
– Example: In Germany, the general fertility rate was
2.12 births per 1,000 women per month in April 2006

10. Specific measures of disease
• Attack rate
– Numerator: number of incident cases of a disease
– Denominator: total population at risk over a restricted
period of observation
– Used frequently in outbreak investigations
– What measure of disease is this?
– Example: respiratory illness attack rate among
members of households in which someone had a
H1N1 diagnosis was 19%

11. Specific measures of disease
• Case-fatality rate
– Denominator: the number of incident cases of a disease
– Numerator: the number of deaths (due to the disease)
– This is a true proportion (the subjects in the numerator must
be in the denominator)
– Example: the Spanish flu of 1918 is reported to have caused 50 mill
deaths among 500 million people infected (10% case-fatality rate)

12. Specific measures of disease
• Death to case ratio
– Numerator: number of deaths attributed to a particular disease over
specified time period
– Denominator: number of new cases of that disease during the same
time period
– Is this a ratio or a proportion?
– Example: In Finland the 28 day death to case ratio for nosocomial
Staphylococcus aureus bloodstream infection was 22/100 between
1995 and 2001

13. Specific measures of disease
• Proportionate mortality
– Numerator: the number of deaths due to a particular
cause
– Denominator: the number of deaths due to all causes
– Each cause must be expressed as a percentage of all
deaths and the sum of all the causes must add to
100%
– Although the term “proportionate mortality” is
infrequently used, the actual concept is frequently
used to present data in newspaper stories (e.g. “the
leading cause of death is…”)
– Example: (next slide)

14. Specific measures of disease
• Of the estimated 8.795 million deaths in children younger than 5
years worldwide in 2008, infectious diseases caused 68% (5.970
million), with the largest percentages due to pneumonia (18%, 1.575
million), diarrhoea (15%, 1.336 million), and malaria (8%, 0.732
million)
• 41% (3.575 million) of deaths occurred in neonates, and the most
important single causes were preterm birth complications (12%,
1.033 million), birth asphyxia (9%, 0.814 million), sepsis (6%, 0.521
million), and pneumonia (4%, 0.386 million)

15. Specific measures of disease
• Proportionate mortality ratio (PMR)
– Numerator: the proportional mortality for a specific
cause in one population or subgroup
– Denominator: the proportional mortality for the same
cause in another population or subgroup

16. Specific measures of disease
• Proportionate mortality ratio for AIDS among children
comparing Africa to the Americas is 4 (4%/1%)
• In Africa the proportion of deaths among children due to
AIDS is 4 times larger than in the Americas

17. Specific measures of disease
• Example: there were 33,199 YPLL in British
Columbia 2001-2005 due to overdose (OD)
mortality (36.5 YPLL/OD)

18. Specific measures of disease
• Years of potential life lost (YPLL)
– Sum of the differences between a predetermined
endpoint and the actual ages of death for those dying
before the predetermined endpoint
– The predetermined endpoint chosen is frequently
either age 65 or the average life expectancy or some
other biologically relevant point
– Measures the impact of premature mortality on a
population

19. Specific measures of disease
• Years of potential life lost (YPLL) rate
– Years of potential life lost per 1,000 population below
age 65
– Allows comparison of premature mortality between
populations

20. Specific measures of disease
• Example: In British Columbia 2001-2005, among
non-First Nations people there were 158.2
YPLL/100,000 due to OD mortality while among
First Nations people there were 464.5 YPLL/100,
000 due to OD mortality