Data issues

• Migration and commuting data sets are very important resource for research and planning since there is no population registration system in the UK and there are no alternative sources that provide data of similar reliability or spatial coverage

• Large and complex data sets with which the user needs to gain some familiarity before using them with confidence

• Shortcomings include problems because of the requirement for the census agencies to preserve confidentiality and lower the risk of disclosure

• In 2001, the approach of ONS to reduce the risk of disclosure was a small cell adjustment method (SCAM), in which values of 1 and 2 were adjusted to either 0 or 3

• Another problem is that geographical boundaries change from year to year, thus obscuring the easy comparison of data over time

• The results of boundary change have prompted the CIDS team to produce estimates of flows from the 1991 and 1981 censuses for 2001 geographical areas