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16a. OBESE ADULTS INDICATOR Upper Tier Local Authority

TABLE 1 – INDICATOR DESCRIPTION

Information component Pg 4 Health Summary – Indicator Number 16
Subject category / domain(s) The way we live
Indicator name (* Indicator title in health profile) Prevalence of obese adults (*Obese adults)
PHO with lead responsibility SEPHO
Date of PHO dataset creation 15/12/2006
Indicator definition Prevalence of obesity, percentage of resident population, adults, 2000-2002, persons
Geography England, GOR, County.
Timeliness Updated annually.
Rationale:What this indicator purports to measure Prevalence of adult obesity
Rationale:Public Health Importance Obesity in adults is defined for epidemiological purposes as body mass index (BMI) > 30 kg/m2. There is an association between all cause mortality and obesity.  Obesity decreases life expectancy by up to nine years. Obesity causes insulin insensitivity, which is an important causal factor in diabetes, heart disease, hypertension and stroke. Obesity is associated with the development of hormone-sensitive cancers; the increased mechanical load increases liability to osteoarthritis and sleep apnoea. Obesity carries psychosocial penalties.  Thus there are many routes by which obesity is a detriment to wellbeing. All these penalties as outlined in the table below (except the risk of gallstones and hip fracture) decrease with weight loss.

Proportion of various diseases attributable to obesity (BMI >27 kg/m2)
Disease
Relative Risk
Attributable proportion (%)
Obesity 100.0
Hypertension 2.9 24.1
Myocardial infarcation 1.9 13.9
Angina pectoris 2.5 20.5
Stroke 3.1 25.8
Venous thrombosis 1.5 7.7
NIDDM 2.9 24.1
Hyperlipidaemia 1.5 7.7
Gout 2.5 20.0
Osteoarthritis 1.8 11.8
Gall-bladder disease 2.0 14.3
Colorectal cancer 1.3 4.7
Breast cancer 1.2 3.2
Genitourinary cancer 1.6 9.1
Hip fracture 0.8 -3.5

Source:  http://hcna.radcliffe-oxford.com/obframe.htmlIt is estimated that obesity costs the NHS over £1 billion per year and society as a whole up to £3.5 billion per year.  Effective interventions exist to prevent and treat obesity.  See NICE guidance – Obesity: the prevention, identification, assessment and management of overweight and obesity in adults and children. http://guidance.nice.org.uk/CG43

Rationale: Purpose behind the inclusion of the indicator To estimate the proportion of obese adults in local authorities.To help reduce the prevalence of obesity.
Rationale:Policy relevance Choosing Health:  Making healthy choices easier.http://www.dh.gov.uk/en/Publicationsandstatistics/Publications/ PublicationsPolicyAndGuidance/DH_4094550 Obesity: Defusing the Health Time Bomb (from the Annual Report of the Chief Medical Officer, 2002).Tackling Obesity:  A Toolbox for Local Partnership Action.Tackling Obesity in England, 2001.
Interpretation: What a high / low level of indicator value means A high indicator value (red circle in health summary chart) represents a statistically significant higher level of estimated adult obesity prevalence when compared to the national value.A low indicator value (yellow circle in health summary chart) represents a statistically significant lower level of estimated adult obesity prevalence when compared to the national value.However obesity at any prevalence level greater than 0 is undesirable, and therefore a low indicator value should not mean that PH action is not needed.
Interpretation: Potential for error due to type of measurement method For each participant in the Health Survey for England, height and weight was recorded by a nurse.  BMI was then calculated for all informants who had valid height and weight measurements, those considered to have unreliable measurements were excluded from the analysis (e.g. pregnant, chair-bound, unsteady or those who could not stand straight).  Those who weighed more than 130kg were asked for an “estimated weight” because the scales were unreliable above this level.  These were included in the analysis.In some sections of the population, applying the BMI classification described above is not always straightforward e.g. when looking at the elderly or different ethnic groups.  For example, in certain Asian populations a given BMI equates to a higher percentage of body fat than the same BMI in a white European population.  In some Black populations, however, the converse is true.  A definition based on waist-hip ratio is often considered a better measure of obesity.  However, BMI is most commonly used and easier to measure routinely.There may also be a discrepancy between these estimates and the lower tier synthetic estimates (districts) which are based on modelled data.  This has lead to inconsistencies between lower tier and county estimates for some areas as the datasets are derived using different methods.
Interpretation: Potential for error due to bias and confounding The Health Survey for England under-samples younger people, people in employment, ethnic minorities, women, those who are healthier but exhibit less healthy behaviour.These data have not been age-standardised and, therefore, variation between area values may be a result of differences in population structure.
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 Prevalence of obesity.Obesity in adults is defined for epidemiological purposes as body mass index (BMI) > 30 kg/m2.
Indicator definition: Statistic Percentage of resident adult population aged 16 and over
Indicator definition: Gender Persons
Indicator definition: age group Adults (aged 16 and over)
Indicator definition: period 2000-2002
Indicator definition: scale
Geography: geographies available for this indicator from other providers Strategic Health Authority. http://www.dh.gov.uk/en/Publicationsandstatistics/ PublishedSurvey/HealthSurveyForEngland/index.htm
Dimensions of inequality: subgroup analyses of this dataset available from other providers Age, gender, ethnicity, social classhttp://www.dh.gov.uk/en/Publicationsandstatistics/ PublishedSurvey/HealthSurveyForEngland/index.htm
Data extraction: Source Health Surveys for England, National Centre for Social Research (NatCen).
Data extraction: source URL Data received directly from NatCen.
Data extraction: date February 2006
Numerator: definition The number of persons aged 16+ who are obese in a sample survey of the health of the population of England.
Numerator: source Health Survey for England (HSE), commissioned by the Department of Health and carried out by the Joint Health Survey Unit of Social and Community Planning Research and of the Department of Epidemiology and Public Health at University College, London.
Denominator: definition Total number of respondents (with valid measurements for height and weight) aged 16+ in the Health Survey for England 2000-2002.
Denominator: source Health Survey for England (HSE), commissioned by the Department of Health and carried out by the Joint Health Survey Unit of Social and Community Planning Research and of the Department of Epidemiology and Public Health at University College, London.
Data quality: Accuracy and completeness The Health Survey for England was designed to provide data at both national and regional level about the population living in private households in England.   It uses a clustered, stratified multi-stage sample design. Each year, 720 postcode sectors were selected as the primary sampling units (PSUs). Before selection, postcode sectors are stratified in order to maximise the precision of the sample. Two stratification levels are used in the selection of PSUs. Postcode sectors are first sorted by Local/Unitary Authority, ensuring correct regional balance. Within each Local Authority, sectors are listed in order of the percentage of households with a head of household in a non-manual occupation.  Those living in institutions were not covered.  One of the effects of using this complex design is that standard errors for survey estimates are generally higher than the standard errors.The numerator and denominator counts used to estimate prevalence are based on a sample of the population in each area and, as such, are not true counts.  For this reason the numerator and denominator data are not shown in the data sheet.

TABLE 3 – INDICATOR TECHNICAL METHODS

Numerator: extraction Not applicable.
Numerator: aggregation /allocation Residency by local authority of each respondent is allocated by postcode of residency.
Numerator data caveats Body mass index is defined as weight (kg) divided by height squared (m2). For adults, four groups are defined according to their BMI: · Underweight – under 20kg/m2; · Desirable weight – 20 to 25kg/m2; · Overweight – 25 to 30kg/m2; · Obese – over 30kg/m2 BMI was calculated for all informants who had valid height and weight measurements. The height of informants who were chair-bound, unsteady, or could not stand straight was not measured. Data for those who were considered by the interviewer to have unreliable measurements (e.g. wearing a wig, turban) were excluded from the analysis. The weight of informants who were pregnant, chair bound, unsteady, or could not stand was not measured. Those who weighed more than 130 kg were asked for an “estimated weight” because the scales were unreliable above this level. These have been included in the analysis.These data have not been age-standardised and, therefore, variation between area values may be a result of differences in population structure.
Denominator data caveats The HSE is a series of annual surveys that began in 1991 with the aim of monitoring the health of the population. It was designed to be representative of the general, non-institutional population living in England. The current “full” sample size of the HSE comprises about 16,000 adults aged 16 and over. For each participant, the survey included an interview and a physical examination by a nurse, at which various physical measurements, tests, and samples of blood and saliva were collected. These measurements provided biomedical information about known risk factors associated with disease and objective validation for self-reported health behaviour.
Methods used to calculate indicator value Estimates are based on pooling together three consecutive years of Health Survey for England data (2000-2002). The general population sample size in 2000 and 2002 was about half the sample size in 2001 owing to the sampling of specific population groups – namely, elderly living in institutions (2000) and children and young adults (2002). To ensure that each year’s sample was given an approximately equal weight in the calculation of the 2000-2002 estimates, respondents in 2000 and 2002 were weighted up by two.
Small Populations: How Isles of Scilly and City of London populations have been dealt with Isles of Scilly are excluded from the dataset; City of London is included in the dataset.
Disclosure Control Not applicable.
Confidence Intervals calculation method The standard errors, and 95% confidence intervals, have been calculated using STATA’s survey module (the svy:mean commands), further details can be obtained from Shaun Scholes at NatCen (s.scholes@natcen.ac.uk).One of the effects of using a complex design is that standard errors for survey estimates are generally higher than the standard errors that would be derived from a simple random sample of the same size.

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