Background and Purpose of ASSIGN
In partnership with researchers at Queen Mary University of London’s Clinical Effectiveness Group, Endeavour Health has developed an address-matching algorithm to link patient health records to geospatial information. Linking people to places can help researchers understand how health is impacted by social and environmental factors, like the characteristics of a household, green space or air pollution. But patient addresses are entered into GP records as free text so the same address can be written in different ways, making data linkage very difficult.
The algorithm, known as ASSIGN (AddreSS MatchInG to Unique Property Reference Numbers), allocates a Unique Property Reference Number (UPRN) to patient records. Every property in the UK already has a UPRN. They are allocated by local authorities and made nationally available by Ordnance Survey. A UPRN gives every address a standardised format, enabling pseudonymised linkage to other sources of data.
ASSIGN compares addresses in the NHS record with the Ordnance Survey's "Address Base Premium" UPRN database, one element at a time, and decides whether there is a match. The algorithm mirrors human pattern recognition, so it allows for certain character swaps, spelling mistakes and abbreviations. After rigorous testing and adjustments, ASSIGN correctly matches 98.6% of patient addresses at 38,000 records per minute. It also includes patients’ past addresses, making it possible to study addresses across the life span.
Researchers at Queen Mary are using the pseudonymised UPRNs to study:
· how the health of household members impacts childhood obesity
· whether overcrowded or multi-generational households are at greater risk from Covid-19
· how to support GPs to identify people living in care homes so they can provide more effective care.
As ASSIGN is open source, it is hoped the algorithm will also be used by other researchers to link data, inform policy and improve population health across England.
Component services
ASSIGN supports two main services
- A Web application that people can use to upload a list of addresses and obtain a list of matched addresses and UPRNs (this article)
- A REST API that systems can use to request a matched address and a UPRN for an address.
UPRN data source
Unique Property Reference Numbers (UPRNs) are property identifiers for every property in Great Britain. Ordnance Survey provides access to these in a number of products, but their AddressBase Premium product is the most comprehensive database. It is derived from local government's NLPG (National Land and Property Gazetteer) as created and maintained by GeoPlace, Ordnance Survey’s OS MasterMap Address Layer 2 and the Royal Mail’s PAF (Postcode Address File). It adheres to British Standard for addressing BS7666, and every property has its Unique Property Reference Number (UPRN) and geographical co-ordinates. It is updated every 6 weeks.
Furthermore, there is an assured link between all addresses associated with a property over its life cycle, and from local authority and Royal Mail sources.
That being the case, if there was a service or application that matched the address from someone's health record to at least ONE of the addresses supplied by Address Base Premium then the UPRN can be derived and linked to the person.
Application Functionality
To access the application the user must either be a user of Discovery, or must create their own account in line with level 1 authentication process. An authenticated user has authority to access the UPRN match user interface. In addition to address matching, if the user wishes to have additional data, the user must have rights to access the OS ABP data, usually via the open Government license.
Inputting an address
There are two main functions available to the user:
- Enter an address of some kind and attempt to get a match
- Upload a list of addresses (between 1 and 100,000) and attempt to get a list of matches
An additional flag entered by the user indicates whether to match only on residential properties or include commercial matches.
A match is presented in one of three forms and the user can select either/ or:
- Plain English address : Simply displaying the address fields and their value,together with information
- JSON structure. This is a machine readable structure which includes the same information and can be processed by a computer more easily than plain English
- CSV file. Suitable for importing into Excel (with a note on converting UPRNs to text) or to a database.
The matching details for an address are described in more detail below
Address match response
The following table explains the information returned following a match attempt.
The term 'Candidate address' is the address entered by the user or submitted in the file. The 'authority address' is an address provided by the Ordnance survery address based premium and may be a post office address or a local authority address.
No match responses
| No match message | Value | Explanation |
|---|---|---|
| Address format | Null address lines | No address lines submitted |
| Insufficient characters | The address format does not appear to contain enough characters to attempt to match (<9) | |
| Post code quality | invalid post code | The post code is an invalid format |
| missing post code | Post code is missing. The address may be matched without a post code but normally a post code is necessary even if incorrect in order to simply narrow down the potential matches | |
| Out of area | The post code is valid but unrecognised and appears to be out of area It should be noted that there will still be an attempt to match the address without a post code or a partial match on a post code. | |
| Matched | false | No match |
Match responses
Whenever there is a positive match, the response includes the qualifier of the match and the pattern of match,
The following information is provided when there is a match.
| Field | Value | Description |
|---|---|---|
| Address format | good | Sufficient characters and if there is a post code it is valid |
| See unmatched | The address quality may still be poor (post code etc) even though there is a match | |
| Matched | True | There was a match. Note that this may not be an exact match |
| UPRN | The unique property reference number provided by the Ordnance survey via the Address Based Premium service | |
| Match qualifier | See values in match algorithm article | The qualifier of the match i.e. whether exact or close etc |
| Classification | The classification code of the property | |
| ClassTerm | The term of the code of the property | |
| Algorithm | the code of the algorithm that ended up with the best match. For example 1-match1 indicates an exact match | |
| ABPAddress | Address components as below: | The Address Base Premium address that match to the candidate address |
| Flat | flat number | |
| Building | name of building | |
| Building number | number of building in street | |
| Dependent thoroughfare | A sub-street or something that is dependent on the street to get to the address | |
| Street | The street the building is on | |
| Dependent locality | An area smaller than a localitu | |
| Locality | A locality or area within a town or village | |
| Town | town | |
| Post code | post code | |
| Organisation | name of organisation if recorded by ABP | |
| Match pattern | see values in article on match algorithm | For the purposes of match pattern reporting the 9 main address fields are rationalised to 5 and the match pattern indicates the approximation of the match and any field manipulation that took polace |
ASSIGN algorithm
main article UPRN address matching algorithms
the algorithms used to match addresses are described in more detail by the UPRN address matching algorithms article.