Flow Data Information System

2001 Census: Special Migration Statistics (Level 2)

Contains migration flows within and between wards in the UK. The set of wards used are as follows:

ST and CAS wards are identical for the most part; however in a few cases small CAS wards have been merged with larger neighbours in order to satisfy output thresholds. No such merging was necessary for Northern Ireland, so there is no distinction between ST and CAS wards there.

The mixture of wards is unique to the 2001 interaction data, and the set have therefore been referred to as interaction data wards.

All the 2001 SMS data have been derived from the 100% sample and include imputed households. Where migrant origins were unknown, these were also imputed.

Disclosure control

Data associated with destinations in England, Wales and Northern Ireland have been modifed via a process known as Small Cell Adjustment Methodology (SCAM). The SCAM process is a disclosure control mechanism. For all tables process using SCAM, interior cells with a 'small' value have been adjusted. 'Small' values are understood to be in the range 0-3. Cells with an initial value of 1 have been rounded to either 0 or 3, with 0 being the more likely result. Cells with an initial value of 3 have also been rounded to either 0 or 3, but with 3 being the more likely result. Cells with initial values of either 0 or 3 have retained these values although in each case it is impossible to distinguish between rounded values and 'genuine' 0s or 3s. All sub-totals and totals have been re-calculated from the rounded cells.

There are three noticeable effects of SCAM

  1. Within-table modification. For the majority of outputs, it will be apparent that a large proportion of cells within any table are either 0 or 3, and that sub-totals and totals within the table are multiples of 3.
  2. Between-table variation. SMS Levels 1 and 2 contain several output tables, with the result that a number of values (e.g. 'total migrants') can be found in more than one table. Due to SCAM, these values may not be consistent between tables.
  3. Between-level variation. The three spatial levels for which the SMS are available were independently subject to SCAM. Thus, if a particular value (e.g. 'total migrants') is calculated by aggregating from one spatial level to a higher one, and compared to the value found in the SMS data set for that higher level, those values are unlikely to be consistent.

Users are advised to ensure that data they use has been calculated by summing the minimum number of base values.

Citation information

The following statements should be attached to all output produced using this data set

Data from this set should be cited in a bibliography as:

Office for National Statistics, 2001 Census: Special Migration Statistics (Level 2) [computer file], UK Data Service

Further information

The following pre-defined totals are available from this data set:

There are 5 tables defined for this data set:

The data are available for the following geographies:

Geographies of origin areasGeographies of destination areas
Supported directly
[i]2001 SMS other origin categories
[i]UK interaction data wards 2001
[i]UK interaction data districts 2001
[i]CIDS 1991/2001 common geography - 'districts'
[i]CIDS 1991/2001 common geography - 'intermediate'
[i]CIDS 1991/2001 common geography - '100 zones'
[i]CIDS 1991/2001 common geography - 'city regions'
[i]UK interaction data wards 2001
[i]UK interaction data districts 2001
[i]CIDS 1991/2001 common geography - 'districts'
[i]CIDS 1991/2001 common geography - 'intermediate'
[i]CIDS 1991/2001 common geography - '100 zones'
[i]CIDS 1991/2001 common geography - 'city regions'
Supported via aggregation
[i]UK Government Office Regions (1999-)
[i]UK Standard Table Wards 2001
[i]United Kingdom - member countries
[i]Great Britain and Northern Ireland
[i]2004 ONS Rural and Urban Area Classification, 2001 CAS Wards
[i]2001 ONS ST Ward Classification Supergroup
[i]2001 ONS ST Ward Classification Group
[i]2001 ONS ST Ward Classification Subgroup
[i]2001 ONS ST Ward Demographic Indicator Deciles
[i]NUTS 2 UK Regions
[i]United Kingdom
[i]2001 CIDER Migration Classification
[i]2001 GB Districts plus Northern Ireland
[i]Great Britain Districts (plus Northern Ireland) 2009-
[i]Travel To Work Areas (TTWAs) 2001
[i]UK Government Office Regions (1999-)
[i]UK Standard Table Wards 2001
[i]United Kingdom - member countries
[i]Great Britain and Northern Ireland
[i]2004 ONS Rural and Urban Area Classification, 2001 CAS Wards
[i]2001 ONS ST Ward Classification Supergroup
[i]2001 ONS ST Ward Classification Group
[i]2001 ONS ST Ward Classification Subgroup
[i]2001 ONS ST Ward Demographic Indicator Deciles
[i]NUTS 2 UK Regions
[i]United Kingdom
[i]2001 CIDER Migration Classification
[i]2001 GB Districts plus Northern Ireland
[i]Great Britain Districts (plus Northern Ireland) 2009-
[i]Travel To Work Areas (TTWAs) 2001

Output for geographies that are only supported via aggregation will take longer than for those supported directly

Table frameworks


Table 1: Age by sex
Total Male Female
Total 1 2 3
 
0 4 5 6
1-2 7 8 9
3-4 10 11 12
5-9 13 14 15
10-11 16 17 18
12-14 19 20 21
15 22 23 24
16-17 25 26 27
18-19 28 29 30
20-24 31 32 33
25-34 34 35 36
35-44 37 38 39
45-59 40 41 42
60-64 43 44 45
65-74 46 47 48
75+ 49 50 51

Table 2: Moving groups
Wholly moving households Other moving groups
Groups 1 2
 
Migrants 3 4

Table 3: Ethnic group by sex
Total Male Female
Total 1 2 3
 
White 4 5 6
All other ethnic groups 7 8 9

Table 4: Moving groups by NS-SEC of group reference person
Wholly moving households Other moving groups
Total 1 2
 
Large employers and higher managerial occupations 3 4
Higher professional occupations 5 6
Lower managerial and professional occupations 7 8
Intermediate occupations 9 10
Small employers and own account workers 11 12
Lower supervisory and technical occupations 13 14
Semi-routine occupations 15 16
Routine occupations 17 18
Never worked and long-term unemployed 19 20
Full-time student 21 22
Not classifiable for other reasons 23 24

Table 5: Moving groups by tenure
Wholly moving households Other moving groups
Total 1 2
 
Owner occupied 3 4
Social rented 5 6
Private rented 7 8