|
Migration statistics produced by the Office for National Statistics (ONS) and the Home Office are blunt instruments for measuring, managing, and understanding migration to and from the UK. They are not accurate enough to measure the effect of migration on population, particularly in local areas, and they are not detailed enough to measure the social and economic impacts of migration, or the effects of immigration policy. Current sources of migration statistics were established at a time when levels of migration were much lower than they are today. These sources are not adequate for understanding the scale and complexity of modern migration flows, despite attempts to improve their accuracy and usefulness in recent years.
Annual estimates of immigration, emigration and net migration are primarily based on a sample of around 5,000 migrants identified through the International Passenger Survey, which is a survey of people travelling through UK air and sea ports. The Government must plan to end reliance on the International Passenger Survey as the primary method of estimating migration: it is not fit for the purposes to which it is put. The ONS and Home Office should move as quickly as possible to measuring immigration, emigration and net migration using e-Borders data. The International Passenger Survey was not primarily designed for the purpose of estimating international migration, but to provide economic data on travel and tourism.
In the year to June 2012, immigration was estimated at 515,000. Around 15% of immigration was by British nationals, around 30% was by nationals of other EU countries, and around 55% was by non-EU nationals. Emigration was estimated at 352,000. Around 44% of emigration was by British nationals, around 24% was by nationals of other EU countries, and around 32% was by non-EU nationals. Net migration, the difference between immigration and emigration, was estimated at 163,000.
Because the migration estimates are based on a survey sample they are surrounded by a margin of error. The 95% confidence interval surrounding the estimate of net migration is around plus or minus 35,000. This means there is a 95% chance that the true value of net migration in any twelve month period falls within a range of around 70,000, and a 5% chance that it falls outside this range. This confidence interval represents the potential statistical error in the estimate that arises from the sample size. Other possible sources of error mean the uncertainty surrounding the estimate is even greater. Respondents may be lying and there can be systemic biases in the willingness of particular groups to participate in the survey.
The Government aims "to reduce net migration from the hundreds of thousands back down to the tens of thousands" by the end of the current Parliament.[1] In the period 2006 to 2010, estimates of net inward migration averaged 209,000 a year. So while the Government's target suggests a ten-fold reduction in net inward migration, in practice it only needs to be roughly halved in order for the Government to achieve its aim.
Migration estimates based on the International Passenger Survey are too uncertain for accurate measurement of progress against the Government's net migration target. We are struck by the advice of the Migration Advisory Committee to the Government that it should aim for net migration of only 50,000 as the only means of being certain that net migration is in fact below 100,000. In the longer term the Government should not base its target level of net migration on such an uncertain statistic: doing so could lead to inappropriate immigration policy.
The statistical uncertainty associated with migration estimates increases when the migrant sample is broken down to identify particular sub-groups of migrants, such as those of a particular nationality, or those moving to or from a particular part of the UK. This limits the extent to which the sample can be used to describe the characteristics of migrants. Furthermore, some migrant characteristics are not recorded at all, such as ethnicity. Migration estimates based on the International Passenger Survey do not provide sufficient detail on the characteristics of people migrating to and from the UK to judge properly the social and economic consequences of migration and the effects of immigration policy. They do not provide accurate estimates of international migration to and from local areas.
ONS and Home Office data are incompatible in several respects. ONS migration estimates contain no information on the immigration status of migrants. It is not possible to tell how many immigrants identified by the ONS entered the UK in particular visa categories. Home Office statistics do not indicate the number of visa holders with valid leave to remain in the UK, or the number who overstay their leave to remain. Some aspects of official migration statistics could be considerably improved if the Home Office and ONS properly recorded and linked the data they already gather. But a full and accurate statistical account of migration to and from the UK also requires the ONS to develop new sources of migration statistics.
| 
