Why do we need to understand household mobility?
People move home for all kinds of reasons: to take up a new job, to up-size when they have a child or down-size when they retire, and after some kind of family event like marriage or divorce. Understanding these patterns of household mobility is extremely important for resource allocation and policy decisions: households need roads, parks and bin collections, children need school places, and everyone needs health service provision.
Mobility patterns also impact upon less tangible but equally important elements of our society: having strong community cohesion and a sense of place are important for everyone. When households move, they change the size and composition of the population in local areas. For example, a retired couple selling their house to a family with two children creates demand for additional school places but also changes the demographic composition of the area, severing established community bonds and forging new ones.
Internal migration is the process which delivers the most substantial change in population at a local level, results from the 2011 Census of Population reveal that ten times more people moved within than immigrated from outside the UK: 6.8 million people made an internal move in the year to March 27, 2011. Internal migration patterns are a crucial component in sub-national population projections which inform forward looking policy. We need timely data which provides good coverage to understand mobility patterns.
Isn’t there a register of migration?
There are several sources of data which report migration within the UK, but no single register like, for example, the one in place in Sweden. The most comprehensive (with the largest coverage) is the Census of Population, which askes for information on where every individual lived twelve months ago. These data are extremely valuable, but have limitations:
- they are only available once every ten years;
- data are not released for a substantial period of time after the census is completed;
- data are released at pre-defined administrative boundaries (the smallest being Output Area);
- they only capture transitions for a single year – the question asks ‘where were you living one year ago’ – so multiple movements that people make during the year are not recorded.
There is debate around the future of the conventional census, given the cost of administering the survey (estimated at £480m for 2011) and the current political agenda for austerity.
Official estimates of migration, released annually, are produced using administrative data from the National Health Service. When an individual informs their GP that they have changed their address the migration record is updated accordingly. Again, this is a hugely valuable resource but problems with these data include:
- under reporting, especially amongst certain groups (e.g. young men who don’t regularly visit their GP);
- geography, as the most detailed spatial units available are local authorities;
- timeliness as the data are only released once per year;
- the data only report one year transitions.
Other administrative data exist, for example the Higher Education Statistics Agency data used to improve estimates of student migration in the official statistics. These administrative data cover sub-groups of the population, and are not inherently intended for the measurement of migration.
The third option is the use of commercial or Big Data resources. Some work has been undertaken previously on these emerging forms of data and their utility for migration research. For example, work by Dr Michael Thomas and Professor John Stillwell uses a commercial survey called Acxiom to assess patterns of movement and distances travelled for the population sample. But, to date, work on demonstrating the utility of commercial data as a viable alternative to census or admin data, is fairly limited.
This is why the opportunity to use a large scale commercial dataset, as presented in this series, is so exciting. Commercial data has the potential to enrich our understanding, but we are not yet at a stage where it can be relied upon as the only source of information.
Accessing property and migration data
The Consumer Data Research Centre has partnered with online property search provider Zoopla and data insight consultancy Whenfresh to obtain data about the characteristics of properties which have been sold in England and Wales. For the 2014 calendar year, there were over 900k unique property transactions.
This data is available to researchers via the CDRC Secure Service:
View WhenFresh/Zoopla Property Rentals and Associated Migration Metadata
View Property Transactions and Associated Migration Metadata
About the author
Dr Nik Lomax is a University Academic Fellow at the University of Leeds, his research focuses on the way in which demographic behaviour changes over time and how people interact with the areas in which they live and work. Much of his work focuses on the dynamic processes involved in migration but he is also interested in the social implications of changing demographic composition: household formation, social exclusion and population ageing for example. Areas are shaped by changing economic conditions, policy interventions and social attitudes, which in turn has an impact on demographic behaviour. Modelling and explaining these complex interaction is key to the work which he does.