Health Heart
Medical

18. LIFE EXPECTANCY FEMALE INDICATOR

TABLE 1 – INDICATOR DESCRIPTION

Information component Pg 4 Health Summary – Indicator No. 18
Subject category / domain(s) How long we live and what we die of
Indicator name (* Indicator title in health profile) Life expectancy – female
PHO with lead responsibility LHO
Date of PHO dataset creation Dec 2006
Indicator definition Life expectancy at birth, years, all ages, 2003-05, males
Geography England, GOR, Local Authority: Counties, County Districts, Metropolitan County Districts, Unitary Authorities, London Boroughs.
Timeliness ONS produced data are updated annually in the Autumn of the following year.
Rationale:What this indicator purports to measure Life expectancy at birth is a summary measure of the all cause mortality rates in an area in a given period. It is the average number of years a new-born baby would survive, were he or she to experience the particular area’s age-specific mortality rates for that time period throughout his or her life.
Rationale:Public Health Importance All cause mortality is a fundamental and probably the oldest measure of the health status of a population.  It represents the cumulative effect of the prevalence of risk factors, prevalence and severity of disease, and the effectiveness of interventions and treatment. Differences in levels of all-cause mortality reflect health inequalities between different population groups, e.g. between genders, social classes and ethnic groups. Life expectancy at birth is chosen as the preferred summary measure of all cause mortality as it quantifies the differences between areas in units (years of life) that are more readily understood and meaningful to the audience than those of other measures.
Rationale: Purpose behind the inclusion of the indicator To help reduce premature mortality and facilitate planning of health services at local level.
Rationale:Policy relevance There is a national health inequalities target for life expectancy which aims to increase average life expectancy at birth in England to 78.6 years for men and to 82.5 years for women, and to reduce health inequalities by 10% by 2010 as measured by life expectancy at birth (Department of Health PSA priority 1).Also life expectancy is an indicator in the following:Local basket of inequalities indicators – Indicator 13.12.Opportunity for all – Communities – Indicator 39.Quality of life indicators – Health and social well-being – Indicator 33
Interpretation: What a high / low level of indicator value means The higher the life expectancy, the longer the estimated life expectancy for males living in that area at that time.
Interpretation: Potential for error due to type of measurement method The figures reflect the contemporary mortality among those living in the area in each time period. They are not the number of years a baby born in the area in each time period could actually expect to live, both because the death rates of the area are likely to change in the future and because many of those born in the area will live elsewhere for at least some part of their lives.Life expectancy at birth is also not a guide to the remaining expectancy of life at any other given age. For example, if female life expectancy at birth was 80 years for a particular area, life expectancy of women aged exactly 75 years in that area would exceed 5 years. This reflects the fact that survival from a particular age depends only on the mortality rates beyond that age, whereas survival from birth is based on mortality rates for all ages
Interpretation: Potential for error due to bias and confounding Older people living in nursing homes tend to be in poorer health than those not living in nursing homes. As these homes are unevenly distributed across the country, a higher death rate – consequently lower life expectancy level – in one area could simply be the result of migration of frail older people moving into nursing homes in that area.
Confidence Intervals: Definition and purpose A confidence interval is a range of values that is normally used to describe the uncertainty around a point estimate of a quantity, for example, a mortality rate. This uncertainty arises as factors influencing the indicator are subject to chance occurrences that are inherent in the world around us. These occurrences result in random fluctuations in the indicator value between different areas and time periods. In the case of indicators based on a sample of the population, uncertainty also arises from random differences between the sample and the population itself.The stated value should therefore be considered as only an estimate of the true or ‘underlying’ value. Confidence intervals quantify the uncertainty in this estimate and, generally speaking, describe how much different the point estimate could have been if the underlying conditions stayed the same, but chance had led to a different set of data. The wider is the confidence interval the greater is the uncertainty in the estimate.Confidence intervals are given with a stated probability level. In Health Profiles 2007 this is 95%, and so we say that there is a 95% probability that the interval covers the true value. The use of 95% is arbitrary but is conventional practice in medicine and public health. The confidence intervals have also been used to make comparisons against the national value. For this purpose the national value has been treated as an exact reference value rather than as an estimate and, under these conditions, the interval can be used to test whether the value is statistically significantly different to the national. If the interval includes the national value, the difference is not statistically significant and the value is shown on the health summary chart with a white symbol. If the interval does not include the national value, the difference is statistically significant and the value is shown on the health summary chart with a red or amber symbol depending on whether it is worse or better than the national value respectively.

TABLE 2 – INDICATOR SPECIFICATION

Indicator definition: Variable Life expectancy at birth
Indicator definition: Statistic Number of years
Indicator definition: Gender Females
Indicator definition: age group All ages
Indicator definition: period 2003-2005
Indicator definition: scale
Geography: geographies available for this indicator from other providers England & Wales, SHAAvailable from the Office for National Statistics (ONS)
Dimensions of inequality: subgroup analyses of this dataset available from other providers Social Class.Available from the Office for National Statistics (ONS)
Data extraction: Source Office for National Statistics (ONS)
Data extraction: source URL www.statistics.gov.uk
Data extraction: date Dec 2005
Numerator: definition Estimated number of years of female life expectancy at birth based on a three-year period for 2003-2005.
Numerator: source Office for National Statistics (ONS).
Denominator: definition N/A
Denominator: source N/A
Data quality: Accuracy and completeness Mortality data quality and coverage is extremely high. The figures are three-year averages so as to provide large enough numbers to ensure that the presented figures are sufficiently robust. Two authorities, City of London and Isles of Scilly, are excluded from the results because of small numbers of deaths and populations in these areas.

TABLE 3 – INDICATOR TECHNICAL METHODS

Numerator: extraction Extraction of the completed indicator from ONS
Numerator: aggregation /allocation Deaths were assigned to local authority boundaries by ONS using the National Statistics Postcode Directory.
Numerator data caveats Source material used to calculate LE:The population estimates used for the calculation of figures for this indicator are based on the 2001 Census. The current interim life tables for 2003-05 are the first set published by ONS. These tables are based on the mid-year population estimates for 2003, 2004 and 2005 and corresponding data on births, infant deaths by individual age from those years.
Denominator data caveats Source material used to calculate LEThe population estimates used to calculate these interim life tables are the estimates, or revised estimates, published on the following dates:Mid-year population estimates for 2003 – 9 September 2004; Mid-year population estimates for 2004 – 20 December 2005; Mid-year population estimates for 2005 – 24 August 2006.
Methods used to calculate indicator value The figures are rolling three-year averages produced by aggregating deaths and population estimates for 2003 – 2005.                                                                           Abridged life tables were constructed using standard methods. Separate tables were constructed for males and females. The tables were created using annual mid-year population estimates and deaths registered in each year. All figures presented here are for life expectancy at birth. The Government Actuary’s Department (GAD) compiles data on life expectancy, using data derived from Registrars General on population and deaths. Data are available in the form of life tables on both a period and a cohort basis. For a detailed description of the standard methods and notation associated with the calculation of life expectancy, see the GAD website:http://www.gad.gov.uk/Life_Tables/Interim_Life_Tables.htmFor Regions, County Districts, Metropolitan County Districts, Unitary Authorities and London Boroughs data are presented for 1995-97 to 2003-2005 and are produced by ONS (including confidence intervals). Data for Counties submitted for 2003-2005 included in the spine charts were calculated using the South East Public Health Observatory life expectancy calculator (http://www.sepho.org.uk/viewResource.aspx?id=8943).
Small Populations: How Isles of Scilly and City of London populations have been dealt with City of London and Isles of Scilly are excluded from the results because of small numbers of deaths and populations in these areas.
Disclosure Control Not applicable
Confidence Intervals calculation method The calculation of the confidence intervals was made using the method developed by Chiang. A report which details research undertaken by the Office for National Statistics on comparing methodologies to enable the calculation of confidence intervals for life expectancy at birth has now been published as No 33 in the National Statistics Methodological Series. This report, “Life expectancy at birth: methodological options for small populations”, also presents research carried out to establish if there is a minimum population size below which the calculation of life expectancy may not be considered feasible. It concludes with a summary of methodological conclusions and considers how these could be applied to the calculation of life expectancy at birth for wards in England and Wales. A copy of the report can be found on the NS website at:http://www.statistics.gov.uk/methods_quality/publications.aspThe SEPHO calculator however also includes an adjustment to include a term for the variance associated with the final age interval as developed by Silcocks. Chiang CL. The Life Table and its Construction. In: Introduction to Stochastic Processes in Biostatistics. New York, John Wiley & Sons, 1968: 189-214.Silcocks PBS, Jenner DA, Reza R.  Life expectancy as a summary of mortality in a population: statistical considerations and suitability for use by health authorities.  J Epidemiol Community Health 2001; 55: 38-4

Posted in: Indicators