1. South West Public Health Observatory
Key Data Sources for
Public Health
Public Health Information and Evidence Seminar
Mark Dancox
4th
November 2010

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. 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. 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. 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. 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. 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. 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. 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. South West Public Health Observatory
Determinants : Factors affecting health
• Health is affected by many factors, as summarised by
Dahlgren and Whitehead’s diagram…

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. 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. 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. 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. 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. 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. 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. 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. 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. Incidence and prevalence
Sick population
(Prevalence)
Healthy
population
Incidence (new cases)
die (mortality)
recover

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. 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. 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. 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. 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. South West Public Health Observatory
Measures in action….Health Profiles

27. South West Public Health Observatory
Measures in action….NCHOD

28. Thankyou
Mark Dancox
Mark.Dancox@swpho.nhs.uk