Life expectancy Stuart Harris Public Health Intelligence Analyst Course – Day 3

Learning objectives Life expectancy Definition of life expectancy How it is calculated Cohort and period life expectancy Healthy life expectancy Disability-free life expectancy

Life expectancy Fundamental measure of the health status of a population Long history of reporting Used globally Expressed in meaningful units Basis for the Government’s PHOF overarching indicators Increase healthy life expectancy Reduce differences in life expectancy and healthy life expectancy between communities

What is current male life expectancy? Life expectancy Male life expectancy at birth England, a) 76.9 years b) 78.9 years c) 80.9 years

What is current female life expectancy? Life expectancy Female life expectancy at birth England, a) 78.9 years b) 80.9 years c) 82.9 years

National variation in life expectancy Males Lowest: Blackpool – 73.8 years Highest: East Dorset – 83.0 years Females Lowest: Manchester – 79.3 years Highest: East Dorset – 86.4 years Life expectancy

South West time trend for life expectancy Life expectancy

Relationship between life expectancy and deprivation Life expectancy

Life expectancy at birth - definition Life expectancy Life expectancy at birth for an area in a given time period is an estimate of the average number of years a new-born baby would survive if he or she experienced the particular area’s age-specific mortality rates for that time period throughout his or her life.

Age-specific mortality rates Life expectancy South West, 2012

Life expectancy definition Life expectancy Life expectancy reflects mortality among those living in an area in each time period Not a prediction of how long a baby could actually expect to live Mortality rates will change People may move

Life expectancy at other ages Life expectancy Female life expectancy at birth, England, = 82.9 years Therefore female life expectancy at age 65 = 17.9 years (i.e – 65) True or false?

Life expectancy at other ages Life expectancy Female life expectancy at age 65 = 21.0 years Life expectancy at birth not a guide to remaining expectation of life at other ages Survival from birth based on mortality rates at every age Survival at other ages depends only on mortality rates beyond that age

How is it calculated? Life expectancy

A life table Life expectancy

16 Width of the 19 age intervals used in this abridged life table. Life expectancy

17 Because deaths in year 1 are not evenly distributed during the year (they are closer to birth), infants deaths contribute less than ½ a year. Estimated as 0.1 x 1 year. Fraction of the age interval lived by those in the cohort population who die in the interval. Life expectancy

18 Population years at risk in age interval Life expectancy

19 Number of deaths in the age interval. Life expectancy

20 Age-specific death rate. Age specific death rate = population number of deaths Life expectancy

21 Conditional probability that an individual who has survived to start of the age interval will die in the age interval. Prob(dying) = ( 1+ Interval width*(1-fraction)*death rate)) interval width *death rate Life expectancy

22 Prob(surviving) = 1 – Prob(dying) Conditional probability that an individual entering the age interval will survive the age interval Life expectancy

23 Life table cohort population. The hypothetical population of newborn babies on which the life table is based. No. alive at start of interval No. alive at start of previous interval x Probability of surviving = Life expectancy

24 Number of life table deaths in the age interval No. of deaths = No. alive at start of interval – No. alive at start of next interval Life expectancy

25 Number of years lived during the age interval. No. years lived = interval width x No. alive at start of next interval + (fraction of age x no. dying) Life expectancy ( )

26 Cumulative number of years lived by the cohort population in the age interval and all subsequent age intervals. Cumulative years lived = No. years lived + No. years lived in all following intervals Life expectancy

27 Life expectancy at the beginning of the age interval. Life expectancy = Total no. years lived beyond interval number alive in interval Life expectancy

28Life expectancy Life expectancy calculator Available at

29 Life expectancy - strengths Life expectancy Meaningful way to provide a summary measure of the mortality experience of a population Directly comparable between populations: over time, between sexes, between areas Easy to calculate with available calculators

30 Life expectancy - limitations Life expectancy Easily misunderstood - difficult to explain and interpret An overall summary of mortality – may mask age or cause-specific changes Not suitable for very small pops (<5,000) For small areas influenced by local characteristics, e.g. infant mortality nursing homes

31 Period life expectancy Life expectancy Results so far are period life expectancies Calculations based on mortality rates for a single period in time for all age groups Makes no allowance for any later actual or projected change in mortality Hypothetical figure - not the number of years someone could actually expect to live

32 Cohort life expectancy Life expectancy Cohort life expectancies are calculated using age- specific mortality rates which allow for changes in mortality over time. May be; Historical – using observed historical mortality rates Current – using projected mortality rates into future Regarded as a more appropriate measure of how long a person of a given age would be expected to live, on average, than period life expectancy

33 Period and cohort life expectancy Life expectancy Period life expectancy at 65 in 2008 is calculated using the mortality rates for those aged 65 in 2008, for 66 in 2008, for 67 in 2008 and so on Cohort life expectancy at 65 in 2008 would be calculated using the mortality rate for those aged 65 in 2008, those aged 66 in 2009, those aged 67 in 2010, and so on

34 Cohort life expectancy Life expectancy Cohort life expectancies may depend on projected mortality rates - subjective If mortality rates are projected to decrease in future years, the cohort life expectancy will be greater than the period life expectancy

35 Period and cohort projections Life expectancy

36 Healthy life expectancy Life expectancy Life expectancy takes no account of the quality of life Increasing life expectancy – are additional years of life lived in good health? Or a prolonged state of illness & dependency? Important question for ageing populations

37 Health expectancies Life expectancy Combine mortality and morbidity into a single index – quality & quantity of life Reflect population’s lifelong experience of health, illness and death Many different health expectancies – as many as there are concepts or measures of health

38 Healthy life expectancy at birth, England Life expectancy Source: ONS

39 Disability-free life expectancy Life expectancy

40 Key points – period life expectancy Life expectancy Reflects mortality among those living in an area in each time period Not a prediction of how long a baby could actually expect to live Life expectancy at birth not a guide to remaining expectation of life at other ages