Household Projections
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Transcript Household Projections
Household Projections
Dorothy Watson
General Register Office for Scotland
Household Estimates and Projections Branch
Four sets of information are used to
produce household projections:
Population Projections
Communal Establishment Rates
Headship Rates
Household Estimates
Overview of Household Projection Process
Population
Projections
Communal
Establishments
Household
Estimates
Private
Population
1991 and 2001
Head of House
Census data
Projected
Headship
Rates
Projected
Households
Household types and age groups
Household projections are produced for each local authority
area, broken down into seven household types (based on the
number of adults and children living in the household and
sixteen age groups.
Household types
1 person households:
1 adult: male
1 adult: female
2 person households:
2 adults
1 adult, 1 child
3+ person households:
1 adult, 2+ children
2+ adults, 1+ children
3+ adults
Age groups
16-19
20-24
25-29
30-34
35-39
40-44
45-49
50-54
55-59
60-64
65-69
70-74
75-79
80-84
85-89
90+
Population Projections
There are three components of population change
Mortality
Fertility
Migration
These three components together with the base population
estimate for the starting year (2008) combine to form a
projection of the population from one year to the next.
Population projections by age group, by gender and by council
area are needed for household projections.
Example:
40 to 44
female
male
2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
7,572 7,486 7,341 7,283 7,268 7,182 7,021 6,816 6,623 6,396 6,323
7,615 7,600 7,540 7,594 7,439 7,455 7,372 7,351 7,302 7,431 7,606
Communal Establishments (CEs)
CEs include residential schools, student halls, adult and children’s care
homes, prisons etc.
The Communal Establishment Rate is the proportion of the population
of a particular age group and gender who are resident in a CE.
40 to 44
female
male
Total
Residents in
Population
CEs
7,572
43.278
7615
85.28
Residents in CEs
Total Population
43.278
7,572
0.005716
CE Rate
CE Rate
0.005716
0.011199
The calculated CE rate for each age group and gender is kept constant for the
entire projection period.
40 to 44
female
male
2008
0.005716
0.011199
2009
0.005716
0.011199
2010
0.005716
0.011199
…
…
…
2016
0.005716
0.011199
2017
0.005716
0.011199
2018
0.005716
0.011199
Private Population
The private population is calculated by subtracting those who live in
CEs from the projected population.
Private Population = Projected Population x (1 – CE rate)
= 7,572 x (1 – 0.005716)
= 7,529
Population Projections
40 to 44
2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
female
7,572 7,486 7,341 7,283 7,268 7,182 7,021 6,816 6,623 6,396 6,323
male
7,615 7,600 7,540 7,594 7,439 7,455 7,372 7,351 7,302 7,431 7,606
Communal Establishment Rates
40 to 44
2008
2009
2010 …
2016
2017
2018
female
0.005716 0.005716 0.005716 … 0.005716 0.005716 0.005716
male
0.011199 0.011199 0.011199 … 0.011199 0.011199 0.011199
Private Population
40 to 44
2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
female
7,529 7,443 7,299 7,241 7,226 7,141 6,981 6,777 6,585 6,359 6,287
male
7,530 7,515 7,456 7,509 7,356 7,372 7,289 7,269 7,220 7,348 7,521
Headship Rates
The proportions of households by council area, household type and age
group of the head of household are known for each of the 1991 and
2001 Census years.
Example
Number and proportion of heads of household aged 40-44 by
household type: Aberdeen City, 2001
1 adult, male
1 adult, female
2 adults
1 adult, 1 child
3+ adults
1 adult, 2+ children
2+ adults, 1+ children
People not head of household
Total people in group
Number
1565
847
1180
390
623
376
4189
6167
15337
Proportion
0.10204
0.05523
0.07694
0.02543
0.04062
0.02452
0.27313
0.40210
1.00000
Projected Headship Rates
The headship (and non-headship rates) are projected forward using the
modified two-point exponential model.
yi k ab
a y1991 k
where:
yi headship rate in year i
k 1 if y2001 y1991
k 0
xi
if
y2001 y1991
y2001 k
b
y1991 k
i 1991
xi
2001 1991
Projected Headship Rates
Example:
The headship rate for 2008 is calculated from the known headship rates
for 1991 and 2001.
Household type
2+ adults, 1+ children
y1991
y2001
0.28227
0.27313
Since 0.27313 < 0.28227 then k = 0 and the equation becomes
20081991
y 2001 20011991
y 2008 y1991
y1991
1 .7
0.27313
0.28227
0.28227
0.26691
Headship rates for other years are calculated in a similar way.
Projected Headship Rates
Age group of head of household = 40 to 44
Household type = 2+ adults, 1+ children
0.5
0.4
Projected headship rates
0.3
0.2
1991 and 2001 Census
headship rates
0.1
0
1991
1996
2001
2006
2011
2016
2021
2026
2031
Constrained Headship Rates
The projected headship (and non-headship) rates are
constrained in two ways
they cannot individually go above1 or below 0
they sum to 1 within an area and age group
householdtype
1 adult 2+ children
1 adult, 1 child
1 person female
1 person male
2 person all adult
2+ adult 1+ children
3+ person all adult
Non-heads
Total
projected headship constrained headship
0.03382
0.03343
0.03364
0.03325
0.06984
0.06903
0.12781
0.12634
0.07492
0.07405
0.26691
0.26382
0.02580
0.02550
0.37896
0.37458
1.01170
1.00000
0.03382 1.01170 = 0.03343
Projected Households
The household projections are calculated by applying the constrained
projected headship rates to the total private population projections.
Total Private Population
40 to 44
2008
TOTAL
15,058
2009
14,958
2010
14,755
…
…
2016
13,805
2017
13,707
2018
13,808
Constrained projected headship rates
40 to 44
2008
2009
1 person female
0.06903 0.07092
2+ adult 1+ children
0.26382 0.26238
2010
0.07279
0.26093
…
…
…
2016
0.08358
0.25190
2017
0.08531
0.25036
2018
0.08702
0.24882
15,058 x 0.06903 = 1,040
Projected households
40 to 44
1 person female
2+ adult 1+ children
2008
1,040
3,973
2009
1,061
3,925
2010
1,074
3,850
…
…
…
2016
1,154
3,478
2017
1,169
3,432
2018
1,202
3,436
Final Adjustments
The projected numbers of households are controlled so that figures
for local authorities sum to the total for Scotland.
The total numbers of households within each local authority are
adjusted to equal the latest annual household estimates. To preserve
trends, projections are also adjusted by the same proportion.
Finally figures are adjusted to ensure that the minimum number of
adults required to fill the projected households is not greater than the
projected private adult population and a similar check is carried out for
children.
The most recent 2008- based household projections for Scotland can
be found on the GROS website
http://www.gro-scotland.gov.uk/