Public Health Key Data Sources

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  • Social marketing being increasingly used in applications such as
    Mosaic, People and Places.
    Fee attached to using some of these. Some of them are free however.
  • Using this set of health indicators we can construct a number of measures summarising the health of a population.
  • There are many factors that can affect health.
    At the biological level, our genetic heritage may make us susceptible to specific conditions such as hypertension, sickle cell anaemia, cancer and haemophilia.
    Then there is how we live – how much we exercise, what we eat, what we drink and what we might smoke. That people in some societies seem to live longer than in others probably reflects differences in the interaction of these factors.
    Then there is the environment. Hippocrates, ‘the father of medicine’, was one of the first to identify the environment as determinant. He noted that the seasons had an impact and the influence of where people lived. It was a prophetic suggestion, later borne out in modern society. Along with the innovations of Industrial Revolution came urbanisation and in particular problems of squalid housing, poor sanitation and polluted water supplies. Concern at the combined effect of these factors gave rise to the first Public Health Act of 1848.
    More latterly, the ‘shrinking’ of the earth through advances in transport has now made it easier than ever for individuals - and diseases – to move freely across the globe. Whilst economic progress has many advantages there can be positive and negative impacts on health.
  • Prevalence is a measure of the population affected by a specific condition at a specific point in time. As such, it is a measure of the probability that a an individual in the population will suffer from the condition of interest.
    Other examples of prevalence are point, period an lifetime prevalence.
    Point prevalence: relates to prevalence with respect to a specific point in time - Did you have an asthma attack on Monday?
    Period prevalence: related to prevalence over a defined period of time - Did you have an asthma attack in January?
    Lifetime prevalence: Have you ever had an asthma attack?
    The Quality Outcomes Framework (QOF) data collected by GPs contains information on the prevalence of specific conditions.
  • Incidence can be thought of as the rate at which new cases are recorded in a specific unit of time amongst the population at risk of developing it. Consequently, people who already have the condition would not be included in the denominator as they are no longer ‘at risk’ as such.
    Note that it is important to specify the time period being used since the number of incident cases can be made arbitrarily large or small depending on the length of the time period being considered.
  • The relationship between incidence and prevalence can also be pictured using the ‘tap’ diagram.
    Here we can see that the number of incident case contribute to the reservoir of those in the population with the condition.
    This reservoir may be depleted by natural means such as death or cure from the condition.
    If the person recovers, they become disease free and so can be legitimately be judged to be a potential incident case once again.
    Note that those who are cured once again become eligible for entry to the ‘at risk of being an incident case’ population.
  • Dividing the total number of cases by the total population at risk during a specific time period provides an estimate of the crude rate.
    As well as being straightforward to understand it also provides a measure of the disease experience in a population. However, the simplicity of the calculation of crude rates is also a shortcoming as it does not take into account the age structure of a population.
    A high crude rate in one area and low crude rate in another may simply reflect differences in age structure between areas rather than any real differences in the occurrence of disease.
  • One approach to looking at the disease experience of a population is by looking at age specific rates.
    This in effect removes the confounding effect of factors such as age and gender and can allow comparisons to be made between populations.
    However, it is not always easy to establish what is going on if there are many different specific rates to consider. The next slide will show what I mean….
  • The method of standardisation provides a method for adjusting for the effects of differing age structures.
    There are two main flavours – indirect and direct – though there are other more specialised methods that could be used.
    Which of these methods is used in practice will depend on what data is to hand and what sort of comparisons are going to be made.
    Comparisons should only be made on a disease-by-disease basis. It is not meaningful to use standardised rates to make comparisons between different diseases.
  • The method of standardisation provides a method for adjusting for the effects of differing age structures.
    There are two main flavours – indirect and direct – though there are other more specialised methods that could be used.
    Which of these methods is used in practice will depend on what data is to hand and what sort of comparisons are going to be made.
    Comparisons should only be made on a disease-by-disease basis. It is not meaningful to use standardised rates to make comparisons between different diseases.
  • There are various different ways in which the extent of disease in a population can be quantified. The Health Profiles published by APHO and the Department of Health include measures such as crude rates and standardised rates.
    Of course, there are numerous other sources of information that can be used such as the National Clinical Health Outcomes database. The aim of this session is to provide some background to the measures that each of these sources use.
  • There are various different ways in which the extent of disease in a population can be quantified. The National Clinical Health Outcomes Database includes various measures such as crude rates and standardised rates for a range of conditions.
    Two versions of NCHOD are available. On is aimed at users in the NHS and the other is intended for consumption by
    The general public. The difference between each of this is principally suppression of low counts in the generally accessible version.
    The aim of this session is to provide some background to the measures that each of these sources use.
  • Public Health Key Data Sources

    1. 1. South West Public Health Observatory Key Data Sources for Public Health Public Health Information and Evidence Seminar Mark Dancox 4th November 2010
    2. 2. South West Public Health Observatory In this session • Main sources of data used in Public Health • Over-view of special methods used to measure the health of a population • Specific data sources for the South West
    3. 3. South West Public Health Observatory First things first • In public health we are often interested in the frequency, distribution and determinants of health problems and disease in populations. • The unit of interest is the POPULATION not the individual.
    4. 4. South West Public Health Observatory What data do we use? • Raw data, only available to NHS employees with appropriate role-based permissions: – Births – Deaths – Hospital Admissions – Cancer Registrations – GP consultations – Prescriptions – A&E attendances – Population • Need to aggregate data so that it can’t be identified
    5. 5. South West Public Health Observatory What’s the distribution? • Often want to tie in frequency information to location. • Consideration of geography is therefore important: – Postcode – Lower Super Output Area – Local Authorities – Primary Care Trusts – Strategic Health Authorities • Need to link geography information to births and deaths data • Social Marketing datasets linkage
    6. 6. South West Public Health Observatory • Mortality – All cause – Specific cause – Place of death • Life Expectancy – General measure of health – At birth – Disability Free • Births – Birth Rate – Infant Mortality Some common types of measures:
    7. 7. South West Public Health Observatory – Widely accepted system of classifying diseases and causes of death developed by the World Health Organisation. – Updated every 10 years or so to keep up with advances in medical knowledge and improvements in methods of diagnoses. – Changes in coding can present problems when looking at the occurrence of specific causes of death through time. – ONS regularly produce data on mortality statistics using the ICD-10 system. ICD-10
    8. 8. South West Public Health Observatory – Infectious and parasitic diseases – Neoplasms – Diseases of the blood and blood forming organs – Endocrinal and Nutritional diseases – Mental and behavioural disorders – Diseases of the circulatory system – Diseases of the respiratory system – Injury, poisoning and certain other causes of external consequences ICD-10 Headings include:
    9. 9. South West Public Health Observatory Hospital Admissions (HES) • Principal source of data on all admissions to NHS hospitals in England. • Data warehouse containing details of all admissions to NHS hospitals in England. • Includes private patients treated in NHS hospitals, patients who were resident outside of England and care delivered by treatment centres (including those in the independent sector) funded by the NHS. • Contains details of all NHS outpatient appointments in England
    10. 10. South West Public Health Observatory Determinants : Factors affecting health • Health is affected by many factors, as summarised by Dahlgren and Whitehead’s diagram…
    11. 11. South West Public Health Observatory What are the determinants ? • Age, sex and constitutional factors • Lifestyle • Agriculture and Food production • Education • Work Environment • Unemployment • Water and Sanitation • Health Care Services • Housing
    12. 12. South West Public Health Observatory Deprivation • Prepared by DCLG • Area based measure based on seven ‘domains’ – Health and Disability – Income – Employment – Education skills and Training – Barriers to housing and services – Crime – Living Environment • Applies to England • IMD2004 and IMD2007 available
    13. 13. South West Public Health Observatory Surveys • Established surveys can provide information on the determinants of health – Health Survey for England – General Household Survey – Longitudinal Study – Active People – National Child Measurement Program
    14. 14. South West Public Health Observatory Health Survey for England • Annual • Questionnaire-based answers with physical measurements and analysis of blood samples. • Blood pressure, height and weight, smoking, drinking and general health are covered every year. • An interview with each eligible person in the household is followed by a nurse visit.
    15. 15. South West Public Health Observatory General Household Survey • Information from people living in households in England • Annual • Data collected on – household and family information – housing tenure and household accommodation – consumer durables including vehicle ownership – employment – education – health and use of health services – smoking and drinking – family information including marriage, cohabitation and fertility – income – demographic information about household members including migration.
    16. 16. South West Public Health Observatory South West Observatory Modules • Further information on the determinants of health can be found via the modules of the South West Observatory: – Economy – Skills and Learning – Planning – Environment – Crime – Culture • State of the South West
    17. 17. South West Public Health Observatory Special methods of measuring public health • Published sources of Public Health data use different methods of measuring the health of a population: – Incidence – Prevalence – Crude Rate – Standardised Rates – (confidence intervals)
    18. 18. South West Public Health Observatory Prevalence Prevalence quantifies the proportion of individuals in a population who have the disease at a specific instant. Total number of cases at a given time Prevalence = Total population at that time Note: No time period is involved here.
    19. 19. South West Public Health Observatory Incidence Incidence quantifies the number of new cases of disease that develop in a population of individuals at risk during a specified time period. Number of new cases in period of time Incidence = Population at risk The denominator, “population at risk” , should consist of the entire population in which new cases can occur.
    20. 20. Incidence and prevalence Sick population (Prevalence) Healthy population Incidence (new cases) die (mortality) recover
    21. 21. South West Public Health Observatory Crude Rate • Is the number of cases in a population divided by the total population during a specific time interval. • Provides information on the experience of the population. • Useful for the allocation of health resources and public health planning. • However if comparing heart disease rates between two populations where one population had a larger proportion of young people then differences in rates might simply reflect the relationship between heart disease and age.
    22. 22. South West Public Health Observatory Category-Specific Rates • To account for different population distributions of a factor of interest we can present and compare category-specific rates. • These are calculated on a subgroup of the population which is defined by stratifying the populations into categories e.g age. • They permit comparisons between different categories within the same population.
    23. 23. South West Public Health Observatory Age standardisation • Occurrence of disease in one area may appear to be higher than in another because: – Population structures are different – One area is older than another • Standardisation used to adjust for the effects of age on mortality rates or other rates • Direct or Indirect • Involves the calculation of numbers of expected events which are then compared with numbers of observed events
    24. 24. South West Public Health Observatory Two Methods of standardisation • Different methods available but ‘Direct’ and ‘Indirect’ methods are most common • Can calculate confidence intervals for each • Which method used depends on the comparisons to be performed and the availability of data
    25. 25. South West Public Health Observatory When to use which? • No right or wrong approach, but… – Direct standardisation useful to compare different areas or through time – Indirect Standardisation useful to determine if disease incidence is high or low in one area.
    26. 26. South West Public Health Observatory Measures in action….Health Profiles
    27. 27. South West Public Health Observatory Measures in action….NCHOD
    28. 28. Thankyou Mark Dancox Mark.Dancox@swpho.nhs.uk
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