joint strategic needs assessment foundation profile - JSNA

Interative Hull Atlas: www.hullpublichealth.org/Pages/hull_atlas.htm More information: www.jsnaonline.org and www.hullpublichealth.org
12.10 Life Expectancy at Birth
Life expectancy at birth is a commonly used method of assessing health, improvements
in health over time, and differences in health between different groups (defined on the
basis of geography, deprivation, social class, smoking status, etc). A common
misconception is that life expectancy at birth measures the expected or average
duration of life of a newborn; it does not. It is a measure of life expectancy assuming
that the current age-specific mortality rates continue throughout an entire lifetime. This
is an unrealistic assumption as mortality rates are likely to change over time. The
current mortality rates at each age (for example, at age 50) are used in the calculation of
life expectancy at birth for a newborn infant, but the mortality rates will not be the same
as the mortality rates in future (for example, in 50 years‟ time when that person is 50
years of age). Advances in healthcare, changes in political and social circumstances,
changes in the prevalence of risk factors and changes in diseases and medical
conditions (such as acquired immunodeficiency syndrome (AIDS), bird „flu, diseases
resistant to antibiotics, etc) and many other factors which influence health and life
expectancy cannot be anticipated, so it is not possible to predict mortality rates at each
single year of age in the future. Therefore, life expectancy at birth (despite its name) is
more generally a measure of current health rather than an expectation of life (i.e.
predicting how long an infant will live).
Life expectancy at birth is frequently used, but it is possible to calculate life expectancy
at any age. For example, life expectancy at age 65 years could be calculated. This will
tend to be closer to the true or actual duration of life than life expectancy at birth would
be for a newborn. This is because trends in mortality rates will tend to be reasonably
gradual, so that the current rates of mortality (on which life expectancy calculation is
based) might be a reasonable prediction of mortality rates in the next 20 years or so (but
not of the next 80 years or so, which is the assumption required for life expectancy at
birth).
Life expectancy at birth is calculated for an arbitrary 100,000 males or females and is
the average of how long they will live based on current age-specific mortality rates (in
the calculations for Hull the mortality rate was obtained directly from local mortality and
population data files).
The calculation involves applying the one year mortality rate to 100,000 males (say 5
deaths per 1,000 live births). On average, 500 of the 100,000 boy infants would die in
their first year of life (their contribution to life expectancy would be calculated 73 ). This
would leave 99,500 boys aged one year who contribute in total 99,500 years to the life
expectancy total (in their first year). Applying the mortality rate to these 99,5000 boys
(say 40 deaths per 100,000 in second year) would mean, on average, 40 would die
within their second year of life. Their contribution for this year would be approximately
73 Many of the infants who die within their first year of life die within the first seven days of life, therefore,
most will contribute only a short period of time (the mean age at death within the first year is used to
estimate their average contribution).
Joint Strategic Needs Assessment Foundation Profile – Hull Health Profile: Release 3. March 2011. 780