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• To provide some background to the projections
• To illustrate why an evaluation of the Markdata projections and the Census is necessary
• To provide a summary of the challenges and the methodology
• To report on progress thus far
• To sketch a possible way forward
Objectives
Background?
• The Department needs to plan water resources and water consumption is partly depend on population growth.
• Markdata was commissioned in 1995 to undertake a set of projections to establish potential water demand over time.
• Geographical areas covered
– Magisterial Districts
– Water Consumption Centres
• At that time census 1996 data were unavailable.
• Base data for this set of projections consisted of “triangulation” between various sources (1991 census data, projected data and Markdata Surveys).
• The 1970 census was also used to inform the base data as this was the last census that covered the whole of South Africa.
Background?
• Various population and economic variables:
– Population growth for the period 1991-1996
– Major indicators of economic growth
– Net migration during 1996
– Indicators of employment and
– Household income during 1996 and
– Gross Geographic Product
• informed future growth potential and individual forecasts was undertaken for each Magisterial District and Consumption Centre up to 2025.
• The purpose of this project would therefore be to assess whether these projections compare favourably to the 2001 census results.
• Boundary changes and migration result in differences at smaller geographical levels especially magisterial district and placenames
Why ?
41
94
50
00
42
07
95
12
44
35
67
63
44
76
79
25
40500000
41000000
41500000
42000000
42500000
43000000
43500000
44000000
44500000
45000000
Nu
mb
er
of
Pe
op
le
1996 2001
South Africa
Comparison between the Census and the IWRP Database
Census IWRP data
Why?
6282
837
6861
886
2797
147
2792
967
8614
608
8358
971
9540
451
9005
558
5042
044
5416
682
3134
758
3033
196
8253
1982
3265
3542
479
3689
968
4544
935
4675
069
0
1000000
2000000
3000000
4000000
5000000
6000000
7000000
8000000
9000000
10000000
Nu
mb
er o
f P
eop
le
Ea
ste
rn C
ap
e
Fre
e S
tate
Ga
ute
ng
Kw
azu
lu-N
ata
l
Lim
po
po
Mp
um
ala
ng
a
No
rth
ern
Ca
pe
No
rth
We
st
We
ste
rn C
ap
e
Provinces
Differences between the Census Data and IWRP data per province (2001)
Adjusted Census Data IWRP adjusted 2001
• Why do we need to compare the projections to the census data ?
– Change over time in demographic trends and in the structure of the economy.
– Most projections rest on assumptions and these assumptions may not hold true for long periods of time. Recent trends are, for instance:
– Any uncertainties associated with an illness such as HIV/AIDS and interventions such as the use of ART - impact difficult to assess.
– Slight errors in the data may be compounded and could deviate majorly in twenty years time
Why ?
Number of households
1996
2001
9.7 m
11.8 m
Average household size
1996
2001
4.5
3.8
• The latter could also be illustrated by the following:
Why ?
Census extrapolated to 2000 Number of People
1950 Prof. Jan Sadie 26,3
1955 Tomlinson Commission
28,7
1973 Prof. Jan Sadie 49,1
1980 JL van Tonder & Willie Mostert
39,4
1988 Prof. Jan Sadie 47,5
1989 Bureau for Market Research
47,6
1995 Prof Charles Simkins 45,4
• At national and provincial level the IWRP data did not differ significantly, but the question remained whether there would be significant differences at magisterial level.
– Differences in the coding system between the 1996 and 2001 census
– Differences in the 2001 Spatial data and the 2001 Alpha-numeric data because of cross-boundary demarcation
Data Challenges ?
– Three data sets were integrated into one:• Population census1996
• Population census 2001
• IWRP Data
– Sorted coding and naming problems and performed data checks
– IWRP data projections obtained for 1995, 2005 and 2015.
– Projected estimates derived for 1996 and 2001 by interpolating.
– Preliminary comparisons performed using adjusted estimates
– Difference measured using the numbers and ratios• Aggregated to National level
• Provincial level and
• Magisterial District
Methodology
Difference per province (2001)
Province IWRP-C IWRP/C % C/IWRP
Eastern Cape 579048.8 1.092164 91.56138
Free State -4180.08 0.998506 100.1497
Gauteng -255637 0.970325 103.0582
Kwazulu-Natal -534893 0.943934 105.9396
Limpopo 374637.8 1.074303 93.08363
Mpumalanga -101562 0.967601 103.3484
Northern Cape -2053.87 0.997511 100.2495
North West 147489 1.041634 96.00297
Western Cape 130133.9 1.028633 97.21643
RSA 411162.4 1.009269 99.08157
– Larger differences possibly mainly attributable to migration
Preliminary Results
– Preliminary analysis indicate a relatively small difference in population size.
– Deviations in 15% of the cases probably still need to be determined since likelihood for larger or smaller population has not yet been established.
– In approximately 5% of the magisterial districts differences would be as a result of the boundary problems.
Ratio IWRP/C Frequency Valid Percent
<= .800000 51 14.44759207
.800001 - 1.439527 283 80.16997167
1.439528 - 8.020000 19 5.382436261
Total 353 100
Way Forward
– Investigate the reasons for differences.
– Refine the analysis.
– The census has not been tested for undercount yet.
– This analysis will inform the next steps where the various components for a changing population need to be investigated looking at fertility, migration, mortality and other factors, etc.
– The placename data need to be integrated to enable a comparison between urban population in the IWRP data.
– Household growth expected to play a significant role in water consumption.