Is it Possible to Accurately Measure Migration?

A few days ago, Britain’s premier right-wing tabloid, the Daily Mail, ran a story entitled ‘Disney World can keep better track of its visitors than Britain’. The story reported on a recent report by a group of British MP’s criticising the inaccuracy and bluntness of the UK’s migration statistics produced by the Office for National Statistics (ONS, the UK government’s statistical bureau). Even for relatively experienced demographers, the report was startling in its findings. For example, the International Passenger Survey (IPS), a voluntary survey for travellers entering and leaving the UK, generated samples that were estimated to be around 0.6% of total migrants. This sample size is barely useful for social scientific research, let alone basing government policy on. The British press were quick to point out the shortcomings of the ONS’s migration statistics, along with the usual mass expression of dismay found on social media. So what’s the root cause of inaccurate statistics? Is this simply an example of poor social research? Or is it the case that measuring migration accurately is a challenge too great for even the finest statisticians?

The report from the Public Accounts Select Committee of the House of Commons summarised the current state of UK migration statistics as being ‘not accurate enough to measure the effect of migration on population’ and ‘not detailed enough to measure the social and economic impacts of migration, or the effects of immigration policy’. This, by any account, is damning stuff. The key culprit being the, now tired, IPS which interviews too few migrants that leave the UK.  Indeed, the data that is squeezed out of these passengers is often too little and not necessarily reliable. This shouldn’t necessarily be read as a criticism of ONS methodology. The IPS was introduced at a time when migration in and out of the UK was much lower than it is today. However, the problem is that the IPS hasn’t been able to keep up with today’s migration levels.

It seems to me that those in the press and the world of social media, who were quick to condemn the integrity of British statistics, probably do not realise the scale of the challenge faced by those whose job it is to keep a tab on those travellers. The study of migration, a seemingly simple concept to understand, is in fact a hugely complicated demographic process to get a grasp on. People migrate for different reasons, for different timescales and to places that are geographically different by an almost infinite amount of measures. Even the process of migration can change the identity, legal or social, of the individual and place that hosts the migrant. Therefore, accounting for all the facets of migration into a single piece of research is a stretching task.

Migration researchers and policy makers are faced with regular headaches when trying to disseminate migration data. A common problem is whether or not international student migration has been accounted for in the statistics. Most of the time they are, even though they are normally regarded as temporary visitors and have a very different social and economic impact on a place compared to families that have moved to a place for work or to escape persecution. Moreover, there is an inherent challenge of properly accounting for ex-pats who have returned to the UK after years of living abroad, immigrants who have chosen to leave there host country for their home country and for immigrants who have adopted British citizenship before leaving again. This comes all before the guesswork that is associated with estimating illegal migrants.

Measuring migration adds several more layers of complexity to the process as every methodology has their disadvantages. The British census is a decadal event which is not regular enough to base any short term policy decisions on. The questions asked by IPS interviewers often do not get enough detail for a proper understanding of the migration process. Even out of the data they do collect, some self-reported migration intentions fail to materialise. Other sources of data such as the Labour Force Surveys, medical statistics and foreign censuses are useful but do not always correlate with the primary sources of data due to discrepancies in the data collection. This is made even more difficult as freedom of movement between EU countries has reduced the imperative to collect migration data.

The proposals by MP’s in this week’s report suggested the ONS should utilise e-Borders data collected by electronic passport machines at UK borders. Admittedly, I was surprised to read that this wasn’t already being utilised. Even so, whilst it will help build a more accurate picture of how many people are passing through UK borders. The demographic data it collects will only be able to tell us so much. It will still be unable to tell the researcher whereabouts in the country the immigrant is going to settle, what their education level is, how healthy they are and how they might change the social fabric of their host community. All of which are facets of migration that are of concern to policy makers and public planners.

Is it possible to accurately measure migration with enough certainty and with enough detail to be relied on? Yes, but it’s likely to be challenging, expensive and not without its faults. A future IPS with more questions is likely to test the patience of the most willing interviewee at an air or ferry port and collecting a greater sample size is likely to generate spiralling costs. Even if something of this order were achievable, it is likely to generate datasets that are too complex to analyse, communicate to the public and base policy on. In any case, because migration is a constant phenomenon, the data would go out of date immediately.

There are no easy answers to the question. The task for the ONS now is to not just address the challenge of measuring migration, but to work on communicating to the public the shortcomings of the current datasets both now and in the future, even if the reliability of the data improves. Many demographers accept that measuring population accurately is an almost impossible task. However, as this week’s report demonstrates, work is being done to improve its accuracy and reliability.

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Edward Morgan

About Edward Morgan

Edward Morgan is an ESRC-PIC funded master's student (starting October 2013) at the London School of Economics studying Population and Development. Edward has specialist interests concerning the way in which global demographic change is shaping the macrogeography of the world as well as the geographies of our everyday lives. Edward is a Geography graduate of the University of St Andrews and a former public health consultant to the Met Office.

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