Computation and Measurement of Risk - Mathematics and Statistics for the Environment - page 203

3. For each person who died before the end point, calculate the person's YPLL by subtracting
the age at death from the end point:

YPLL individual = End point - Age at death

4. Sum the individual YPLLs:

YPLL = ∑YPLL individual

8.4.5.2 Method for Calculating YPLL from a Frequency

1. Ensure that age groups break at the identified end point (e.g., 65 years). Eliminate all age
groups older than the endpoint.

2. For each age group younger than the end point, identify the midpoint of the age group,
where midpoint is determined as

Agegroup's youngest ageinyearsoldestag + ee1 +

2

3. For each age group younger than the end point, identify that age group's YPLL by subtract-
ing the midpoint from the end point.

4. Calculate age-specific YPLL by multiplying the age group's YPLL times the number of
persons in that age group.

5. Sum the age-specific YPLLs.

The YPLL rate represents years of potential life lost per 1000 population below the end-point
age, such as 65 years. YPLL rates should be used to compare premature mortality in different popu-
lations, because YPLL does not take into account differences in population sizes. The formula for
YPLL rate is as follows:

Yearsof potential lifelost
Popul

×10 n YPLL rate =

ation underage 65 years

8.5 NATALITY (BIRTH) MEASURES
Natality measures are population-based measures of birth. These measures are used primarily by
persons working in the field of maternal and child health. Table 8.8 includes some of the commonly
used measures of natality.

TABLE 8.8
Frequently Used Measures of Natality

Measure Numerator Denominator 10 n

Crude birth rate Number of live births during a specified

time interval

Mid-interval population 1000

Crude fertility rate Number of live births during a specified

time interval

Number of women ages 15
to 44 at mid-interval

1000

Crude rate of natural increase Number of live births minus number of

deaths during a specified time interval

Mid-interval population 1000

Low-birth-weight ratio Number of live births < 2500 grams

during a specified time interval

Number of live births during
the same time interval

100