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Projecting transient populations - pragmatism or technical correctness? BSPS Conference Sep 2004 Richard CooperResearch team Nottinghamshire County Council. Joint Structure Plan housing figures. Regional Planning Guidance (1996-based) – 49,000 dwellings 2001-21 - PowerPoint PPT Presentation
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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
Comparison of 2021 populations using/ not using a transient population: Nottingham City
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
Comparison of 2021 populations using/ not using a transient population: Nottingham City
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
10000
15000
20000
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
20000
25000
30000
35000
0-4
10-
14
20-
24
30-
34
40-
44
50-
54
60-
64
70-
74
80-
84
2001
2021
NCC DD proj
Main difference is higher 35-54 population in JSP