household projections dorothy watson general register office for scotland household estimates and...
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Household ProjectionsDorothy Watson
General Register Office for ScotlandHousehold 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
Private Population
Projected Headship
Rates
Projected Households
Household Estimates
1991 and 2001 Head of House Census data
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 types1 person households: 1 adult: male 1 adult: female2 person households: 2 adults 1 adult, 1 child3+ person households: 1 adult, 2+ children 2+ adults, 1+ children 3+ adults
Age groups16-1920-2425-2930-3435-3940-4445-4950-5455-5960-6465-6970-7475-7980-8485-8990+
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 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018female 7,572 7,486 7,341 7,283 7,268 7,182 7,021 6,816 6,623 6,396 6,323male 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.
005716.0
572,7
278.43
Population Total
CEsin Residents Rate CE
The calculated CE rate for each age group and gender is kept constant for the entire projection period.
40 to 44 2008 2009 2010 … 2016 2017 2018female 0.005716 0.005716 0.005716 … 0.005716 0.005716 0.005716male 0.011199 0.011199 0.011199 … 0.011199 0.011199 0.011199
40 to 44 Total
PopulationResidents in
CEs CE Ratefemale 7,572 43.278 0.005716male 7615 85.28 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
40 to 44 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018female 7,572 7,486 7,341 7,283 7,268 7,182 7,021 6,816 6,623 6,396 6,323male 7,615 7,600 7,540 7,594 7,439 7,455 7,372 7,351 7,302 7,431 7,606
Population Projections
40 to 44 2008 2009 2010 … 2016 2017 2018female 0.005716 0.005716 0.005716 … 0.005716 0.005716 0.005716male 0.011199 0.011199 0.011199 … 0.011199 0.011199 0.011199
Communal Establishment Rates
40 to 44 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018female 7,529 7,443 7,299 7,241 7,226 7,141 6,981 6,777 6,585 6,359 6,287male 7,530 7,515 7,456 7,509 7,356 7,372 7,289 7,269 7,220 7,348 7,521
Private Population
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 Proportion1 adult, male 1565 0.102041 adult, female 847 0.055232 adults 1180 0.076941 adult, 1 child 390 0.025433+ adults 623 0.040621 adult, 2+ children 376 0.024522+ adults, 1+ children 4189 0.27313People not head of household 6167 0.40210Total people in group 15337 1.00000
Number and proportion of heads of household aged 40-44 by household type: Aberdeen City, 2001
Projected Headship Rates
The headship (and non-headship rates) are projected forward using the modified two-point exponential model.
19912001if
19912001if
yearin rate headship
0
1
yyk
yyk
iiy
ii
xabky
where:
19912001
1991
1991
2001
1991
i
x
ky
kyb
kya
i
Projected Headship Rates
Example:The headship rate for 2008 is calculated from the known headship rates for 1991 and 2001.
2+ adults, 1+ children 0.28227 0.27313
Household type 1991y 2001y
Since 0.27313 < 0.28227 then k = 0 and the equation becomes
26691.0
28227.0
27313.028227.0
7.1
19912001
19912008
1991
20011991 2008
y
yyy
Headship rates for other years are calculated in a similar way.
Projected Headship Rates
0
0.1
0.2
0.3
0.4
0.5
1991 1996 2001 2006 2011 2016 2021 2026 2031
Age group of head of household = 40 to 44
Household type = 2+ adults, 1+ children
Projected headship rates
1991 and 2001 Census headship rates
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 projected headship constrained headship1 adult 2+ children 0.03382 0.033431 adult, 1 child 0.03364 0.033251 person female 0.06984 0.069031 person male 0.12781 0.126342 person all adult 0.07492 0.074052+ adult 1+ children 0.26691 0.263823+ person all adult 0.02580 0.02550Non-heads 0.37896 0.37458Total 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.
Constrained projected headship rates40 to 44 2008 2009 2010 … 2016 2017 20181 person female 0.06903 0.07092 0.07279 … 0.08358 0.08531 0.087022+ adult 1+ children 0.26382 0.26238 0.26093 … 0.25190 0.25036 0.24882
Total Private Population40 to 44 2008 2009 2010 … 2016 2017 2018TOTAL 15,058 14,958 14,755 … 13,805 13,707 13,808
15,058 x 0.06903 = 1,040
Projected households40 to 44 2008 2009 2010 … 2016 2017 20181 person female 1,040 1,061 1,074 … 1,154 1,169 1,2022+ adult 1+ children 3,973 3,925 3,850 … 3,478 3,432 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/