Origin-Destination Flow data

Question 1

What questions on OD flow are included in the census?

Answer 1

− Question on usual residence (on Census day) and residence one year previously [Migration]
− Also included are questions on address of workplace and daily journey to work [Commuting]
− These questions provide migration and commuting flow data

Question 2

What various migrant variables are there?

Answer 2

− Migrant: person with different usual address one year ago to that at time of Census
− Migrant household: household whose head is a migrant
− Wholly moving household: household all of whose residents aged one and over were moving from the same previous address
− Other moving group: (2001 Census only) one or more people moving from the same previous address together

Question 3

How can you access this data?

Answer 3

UK data service

Question 4

What is SMS/SWS/STS? And which censuses were they included in?

Answer 4

1991 Census
− Special Migration Statistics (SMS)
− Special Workplace Statistics (SWS)
2001/2011 Census
− Special Migration Statistics (SMS) for UK
− Special Workplace Statistics (SWS) for England, Wales and NI
− Special Travel Statistics (STS) for Scotland (include travel to place of study as well as place of work)

Question 5

How did the ONS maintain confidentiality in 1991 census?

Answer 5

Supression

Question 6

Why was suppression not successful?

Answer 6

− It was widespread
− Unnecessary
− Prevented accurate analysis of SMS
− Rees and Duke-Williams (1997) developed a series of methods to ‘recover’ suppressed data and have estimated ‘complete’ SMS matrices

Question 7

What method was used in the 2001 census to maintain confidentiality?

Answer 7

Small Cell Adjustment Method (SCAM)
− Flow counts of 1 and 2 at any one level (e.g. OAs, wards and districts) were adjusted to be either 0 or 3
− Means that at any one level, the flows in different tables will not be equal

Question 8

What are the uses of interaction data?

Answer 8

− Migration data used by Government to produce mid-year population estimates and projections
− Census is only comprehensive source of data on commuting, allowing research on characteristics of commuters or spatial patterns of commuting
− Commuting flows used by Government to define Travel To Work Areas

Question 9

What are some other non-Census data sets for Origin-Destination data?

Answer 9

− Migration Data
− Labour Force Survey (LFS)
− International Passenger Survey (IPS)
− National Health Service Central Registers (NHSCR)
− Other administrative sources
− Commuting Data
− National Travel Survey (NTS)
− Pupil Level Annual School Census (PLASC) for pupil journeys to school
− Hospital Episode Statistics (HES) for patient journeys to hospitals

Question 10

What are Gross Migration flows and intensities?

Answer 10

Total number of people moving from one place to another

Question 11

What is Migration Churn?

Answer 11

Number of people who go in an area, number of people who go out and the number who move within the boundaries

Question 12

What are Net Migration flows and intensities?

Answer 12

− Net migration as a % of the usually resident population

− Standardizes by population

Question 13

What are Indices of migration efficiency/effectiveness?

Answer 13

Tells us how efficient net migration is in redistributing the population in a system
Defined in different ways depending on system involved
− Can be expressed as a zone-specific ratio
MERi = 100 (Di - Oi)/(Di + Oi)
− i.e. net migration as a % of total out-migration plus total in-migration
− Can also be expressed as an origin-destination-specific ratio:
− MERij = 100 (Mji - Mij)/(Mji + Mij)