joint structure plan housing figures

Projecting transient populations - pragmatism or technical correctness?

BSPS Conference Sep 2004

Richard Cooper Research teamNottinghamshire County Council

Joint Structure Plan housing figures

• Regional Planning Guidance (1996-based) – 49,000 dwellings 2001-21

• Joint Structure plan accepts total• Distribution to sub-areas• South Nottinghamshire = 37,000• Nottingham City – supply of 18,500

Population projections for Nottingham City

• Basis is a ‘set’ number of dwellings• Early projections were dwelling-led but –

– Migration levels varied widely– Migration-led projection needed– More robust output– More up-to-date information available

• City wanted age / gender projection

Knowns and unknowns

• How many houses – but not types of house, household or occupants

• Age/gender of residents and migrants – but not future migrants

• Characteristics of residents – but not how those may change

Modelling the population

• Changing housing provision (e.g. more flats)• Assumptions that data in the model will still

pertain - – the migration profile remains the same– characteristics (fertility, household

generation, etc.) of population remain same for age, gender & relationship

Nottingham City – 2001 Census

Nottinghamshire (rest of Plan Area) – 2001 Census

Age profile of some JSP districts

0.0%2.0%4.0%6.0%8.0%

10.0%12.0%

0-- 4

10--

14

20--

24

30--

34

40--

44

50--

54

60--

64

70--

74

80--

84

Nottingham UA

Bassetlaw

Broxtowe

Plan Area

Comparison of 2021 populations using/ not using a transient population: Nottingham City

0

5000

10000

15000

20000

25000

30000

350001 2 3 4 5 6 7 8 9

10

11

12

13

14

15

16

17

182001 Population


0

5000

10000

15000

20000

25000

30000

350000

-- 4

5--

9

10

-- 1

4

15

-- 1

9

20

-- 2

4

25

-- 2

9

30

-- 3

4

35

-- 3

9

40

-- 4

4

45

-- 4

9

50

-- 5

4

55

-- 5

9

60

-- 6

4

65

-- 6

9

70

-- 7

4

75

-- 7

9

80

-- 8

4

85

+

Zero transient pop.

2001 Population


0

5000

10000

15000

20000

25000

30000

350000

-- 4

5--

9

10

-- 1

4

15

-- 1

9

20

-- 2

4

25

-- 2

9

30

-- 3

4

35

-- 3

9

40

-- 4

4

45

-- 4

9

50

-- 5

4

55

-- 5

9

60

-- 6

4

65

-- 6

9

70

-- 7

4

75

-- 7

9

80

-- 8

4

85

+

NCC transient pop

2001 Population

Nottingham city projection – no transient population

2001 2006 2011 2016

20-24 30,800 21,029 21,213 19,96825-29 20,400 29,710 19,974 20,14630-34 21,100 19,605 28,868 19,16935-39 19,900 20,538 19,052 28,27140-44 16,300 19,595 20,238 18,769

Effects of ignoring the transient population

• Age structure would have many more adults 35-44, (and fewer 15-24)– ageing through fertile and household

creation ages• For a set number of dwellings (18,500)

– 8,000 fewer (30% less growth)• For a certain migration level

– 2,500 more dwellings

But why is this a problem (to Notts!) ?

• Decision to use Patient Register data– From ONS & used in mid-year estimates– More up-to-date– More complete than the Census (includes

students)– 3 years data - 1997-2000– More accurate?

Comparison of 1997-2000 Patient Register and 1991 Census migration structure (M&F)

-2000

-1000

0

1000

2000

3000

4000

0-4

5-9

10-1

4

15-1

9

20-2

4

25-2

9

30-3

4

35-3

9

40-4

4

ONS patient register97-00 (3 years)

1991 Census

Total net migration:1991 - -1,9002000 - -2,200

A problem ? (2)

3,000 more net in-migrants 15-19 – but are these all students?

Comparison of gross migration: Patient Register & 1991 Census

PR in

PR out Census inCensus out

0

1000

2000

3000

4000

5000

6000

7000

0-4 5-9 10-14

15-19

20-24

25-29

30-34

35-39

40-44

45-49

50-54

55-59

60-64

65-69

70-74

75+

PR in

PR out

Census in

Census out

Gross each w ay f low s:Census: 28-30,000ONS PR: 17-19,000

A problem ? (3)

• Transient population used where migration data does not handle flows adequately (1991 Census)

• If migration data complete there is no need for a transient population - in theory OK

• However, results did not show sensible outcome – it appeared that some student migrants were being excluded

Determining a transient population• Needed a reality check• Thought that transient population in CPHM was

wrong for application to Patient Register migration• How do you decide on a transient population when

some information is missing?• What should the relevant (20-24) population be

doing?• It does not remain absolutely constant, even though

student numbers may do so – so how does it change?

• Look at births 20 years ago, not for absolute numbers – but for trends

What the 20-24 year old projectionss should be showing

Year of births

20 to 24 years old in:

Births Difference from previous period (A)

1977-1981 2001 17,188 n/a1982-1986 2006 19,687 2,5001987-1991 2011 21,885 2,1981992-1996 2016 20,188 -1,697

Changes to 20-24 yr old population 2001 - 2016

Original projection has no transient adjustment

May 2003 resulted from City suggestion in setting transient population

Mar 2004 accounts for latest information and migration-led projection

From birthsOriginal

projection May 2003 Pr. Mar 2004 Pr.2006 2,500 -9,771 229 8422011 2,198 184 184 1,0172016 -1,697 -1,245 -1,245 -2,006

How does it compare? (1)

JSP DD projection - Nottingham

0

5000

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15000

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25000

30000

35000

0-4

10-

14

20-

24

30-

34

40-

44

50-

54

60-

64

70-

74

80-

84

2001

2006

2011

2016

2021

How does it compare? (2)

ONS 96-based (trend) projection - Nottingham

0

5000

10000

15000

20000

25000

30000

35000

40000

0-4

10-

14

20-

24

30-

34

40-

44

50-

54

60-

64

70-

74

80-

84

2001

2006

2011

2016

2021

NB 1996 trend-based, so unusable for Structure Plan

Methodology incorporated separate student ‘adjustment’

How does it compare? (2)CPHM (default) and JSP DD projections - Nottingham

0

5000

10000

15000

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0-4

10-

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74

80-

84

2001

2021

NCC DD proj

Main difference is higher 35-54 population in JSP

joint structure plan housing figures

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