Comparison between Census and WIPR data

Date: 21 September 2004

• 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 ?

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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

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5000000

6000000

7000000

8000000

9000000

10000000

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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.

Data Challenges ?

•

– 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 ?

– Code and name differences worse at the placename level

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.

Sample table slideThank you