The data is from the National Office for Statistics and “estimates are prepared using data from former Health Authority patient registers and these are combined with migration data from the National Health Service Central Register to give internal migration estimates. The mid-2001-mid 2002 to mid-2007 to mid-2008 internal migration estimates by local authority were revised on 13 May 2010 to include the student adjustment.”
As can been seen from the above chart the estimated number of those leaving (outflow) or moving to (inflow) Anglesey is roughly equal each year (shown in thousands in chart a). For the period 1999 to 2009, the total difference between inflow and outflow was a net gain of 400.
If we look at the age groups this shows a consistent net outflow in the 16-24 group (shown in thousands in chart b) and a net inflow in the 45-64 group.
In contrast, the figures for Gwynedd are more varied, you could not compare the two directly for various reasons, Gwynedd in example has the National Park.
As with Anglesey the outflow, inflow each year are broadly similar, however in Gwynedd over the 10 years there has been a greater variation (again figures shown in thousands in chart c).
For the Age group 16-24 whereas in Anglesey the net balance is a constant outflow, for Gwynedd it varies over time, in some years there is a net inflow, as shown in thousands in chart d below
For clarification - net outflow or net inflow is based on the balance of the yearly inflow minus the yearly outflow for a particular age group.