Analysis: Immigration impact 'hard to predict'
The effects of immigration are nuanced and difficult to predict, depending on who is arriving and what state Britain is in when they turn up.
That is the conclusion of a report, revealed by Newsnight, showing a weaker link between immigration and unemployment among British people than the government has previously claimed.
In 2012 Home Secretary Theresa May said: "There is a clear association between non-European immigration and employment in the UK.
"Between 1995 and 2010... for every additional 100 immigrants, they estimated that 23 British workers would not be employed."
But the report suggests the effects of immigration are much more complicated.
It says there is "relatively little evidence that migration has caused significant displacement of UK natives… in periods when the economy is strong".
It notes "evidence of some labour market displacement, particularly by non-EU migrants in recent years when the economy was in recession", but adds that where this has happened, it is a short-term effect "likely to dissipate over time".Narrowly drawn
That difference between the effects of migration during growth or recession explains why the research cited by Mrs May was so pessimistic - it had included data from the 2009-10 recession.
When those years were excluded from the analysis, the impact of non-EU migrants became difficult to pick out.
The new report also notes that academics have yet to be able to spot impacts from EU migrants on jobs.
The authors note, however, this may be because of a lack of useable data - just one of the practical problems in examining the impact of immigration.
This kind of research is also difficult to interpret.
Academics may find small impacts because the effects of immigration are weak and spread over the whole country or because they are strong but concentrated on to some sectors, regions or people.
The report also notes serious problems with the techniques used to examine these questions, which means that much of the research can only be used "tentatively".
There is a very big question mark over a major part of the statistical modelling.
Furthermore, the research is very narrowly drawn - the issues it looks at are just some of the impacts of immigration.
It does not seek to cover all of the economic impacts, let alone the cultural or social effects of large movements of people.
Even so, this report is of some significance in Whitehall - the coalition is not expected to meet its target of reducing immigration to below 100,000 people a year by 2015.
New measures to cut the inflow of migrants, however, may be opposed by Liberal Democrats - and the new research findings will replace more downbeat ones when civil servants attempt to add up the costs of immigration.