REPUBLIC OF SLOVENIA
ANNUAL QUALITY REPORT
FOR THE SURVEY
PUBLIC SEWAGE SYSTEM
FOR
2011
Prepared by: Saša Čuček, Martin Šteharnik
Date: October 2012
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Phone: +386 1 241 51 00; fax: +386 1 241 53 44; E-mail: [email protected]; www.stat.si
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Table of Contents
0
1
2
3
4
5
6
7
Basic Data .......................................................................................................................... 3
Relevance ........................................................................................................................... 4
1.1 Rate of Missing Statistics ............................................................................................ 4
Accuracy............................................................................................................................. 4
2.1 Sampling Errors ........................................................................................................... 4
2.1.1
Sampling Error ................................................................................................... 4
2.2 Non-sampling Errors ................................................................................................... 4
2.2.1
Non-response Errors ........................................................................................... 4
2.2.1.1 Unit Non-Response Rate .................................................................................... 4
2.2.1.2 Item Non-response Rates ................................................................................... 4
2.2.1.3 Imputation Rate .................................................................................................. 4
2.2.2
Coverage Errors .................................................................................................. 5
2.2.2.1 Over-coverage Rates .......................................................................................... 5
2.2.2.2 Misclassification Rates ....................................................................................... 5
2.2.3
Measurement Errors ........................................................................................... 5
2.2.3.1 Editing Rate ........................................................................................................ 5
Timeliness and Punctuality ................................................................................................ 5
3.1 Timeliness .................................................................................................................... 5
3.1.1
Timeliness of the First Release .......................................................................... 5
3.1.2
Timeliness of Final Results ................................................................................ 6
3.2 Punctuality ................................................................................................................... 6
3.2.1
Punctuality of the First Release .......................................................................... 6
Accessibility and Clarity .................................................................................................... 6
4.1 Accessibility ................................................................................................................ 6
4.1.1
Channels used for the dissemination of the results ............................................ 6
4.1.2
Rate of Used Channels ....................................................................................... 6
4.1.3
Means used for the dissemination of the results ................................................ 7
4.1.4
Rate of Means Used ........................................................................................... 7
4.2 Clarity .......................................................................................................................... 7
4.2.1
Results Presented................................................................................................ 7
4.2.2
Level (Detail) of Presentation ............................................................................ 7
Comparability ..................................................................................................................... 8
5.1 Comparability over Time............................................................................................. 8
5.1.1
Length of Comparable Time Series ................................................................... 8
5.1.2
Breaks in Time Series ........................................................................................ 8
5.2 Geographical Comparability........................................................................................ 8
5.2.1
Comparability with Other Members of the European Statistical System .......... 8
5.3 Seasonal Adjustment ................................................................................................... 8
Coherence ........................................................................................................................... 9
6.1 Coherence between Provisional and Final Data .......................................................... 9
6.1.1
Coherence between Provisional and Final Data ................................................. 9
6.2 Coherence with the Results of the Reference Survey.................................................. 9
6.2.1
Reference Survey ............................................................................................... 9
6.2.2
Coherence with Reference Data ......................................................................... 9
Costs and Burdens .............................................................................................................. 9
7.1 Survey Costs of the Office........................................................................................... 9
7.2 Costs and Burden of Reporting Units .......................................................................... 9
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0
Basic Data
Brief Description of the Survey
With the annual questionnaire on the public sewage system we monitor the data regarding the
amount of waste water, the degree of waste water treatment, the amount of undertreated waste
water by place of release and the sewage system.
The statistical survey on the public sewage system is a component part of the surveys from
the field of environment and natural resources.
Observation Units
Observation units are business entities which are according to the 2008 Standard
Classification of Activities (OJ RS No. 69/2007) classified in section E (water supply;
sewerage, waste management and remediation activities), divisions 36 (Water collection,
treatment and supply) and 37, subclass 37.000 (Sewerage) and other entities which took over
the management of sewage systems (treatment facilities of municipalities, public-private
partnerships, etc.).
Coverage
There is full coverage, so the survey covers the entire population, i.e. all the reporting units
which perform the public services of discharge of waste water and of cleaning the communal
waste water and run-off rain water or took over the management of the sewage system.
In case the manager of the sewage system manages more systems (within one municipality or
several municipalities), s/he fills in a questionnaire for each sewage system.
The list of reporting units is being supplemented with data on the managers of the sewage
system from the database of the Ministry of the Environment and Spatial Planning (MESP). In
2011 101 reporting units conducted the survey.
Key variables
In the survey on the Public sewage system, the key variables are as follows:
- The waste water in view of the source of pollution
- The degree of waste water treatment
- The release of waste water by place of release.
Key statistics
In the survey on the Public sewage system, the key statistics are:
- The quantity of waste water by source of pollution
- The amount of treated waste water by degree of treatment
- The amount of released waste water by place of release.
Sewage waste water originates from several activities. We present it by the source of pollution
which is by the following activities: agriculture, forestry and fishing, industrial activities
(mining and quarrying, manufacturing, electricity supply, construction), other activities and
households. The sewage system is filled with other waters as well, e.g. run-off rain water,
water from the hinterland, etc. Waste water is purified during physical and chemical
procedures in the treatment plants and therefore it is divided by the degree of purification into
the primary, secondary and tertiary treatment. Discharged waste water is divided by the
location where it is discharged (indirectly or directly), into the groundwater, into water
courses, into accumulations, into lakes and into the sea.
Questionnaire
The questionnaire is available in Slovene on the web site:
http://www.stat.si/doc/vprasalniki/VOD-K_2011.pdf
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1
Relevance
1.1
Rate of Missing Statistics
The rate of missing statistics is 0.
2
Accuracy
2.1
Sampling Errors
Sampling Error
The survey is not conducted on the basis of a random sample; therefore there is no sampling
error.
2.2
Non-sampling Errors
Non-response Errors
Unit Non-Response Rate
The indicator illustrates the share of units which did not send us any of the requested data.
This share is determined as the ratio between the number of units for which we received no
data and the number of all adequate units. The table below presents indicators for the 20062011 period.
Table 2.1: Unit non-response rate
2006
Number of adequate
92
units
Number
of
non0
responses
Non-response rate
0%
2007
96
2008
96
2009
98
2010
98
2011
98
0
0
0
0
0
0%
0%
0%
0%
0%
Item Non-response Rates
In the survey there is no case of unit non-response if the reporting unit managed the sewage
system in the observed year. In fact we verify already in the phase of data editing whether the
key variables are completed in the questionnaires. If they were not, we contact the reporting
unit by phone and acquire the missing data.
Imputation Rate
In the VOD-K survey we do not impute (fill in) the missing data, but we rather provide (by
phone, in writing) that we receive all the key data.
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Coverage Errors
Over-coverage Rates
The table below presents the over-coverage rate for all the units in the frame. We can see that
since 2006 the over-coverage rate is falling, as the number of the reporting units (in view of
the concession awarded for the implementation of the public service of draining and treating
the communal and run-off rain water) became stable. Namely, when preparing the frame still
prior to 2006, we did not have sufficient information on the units which were awarded the
concession for managing the sewage systems, or these were no longer active as they
terminated the activity (due to various reasons).
Table 2.2: Over-coverage rate
2005
Number of units in
103
frame
Number
of
8
inadequate units
Over-coverage rate
8%
2006
103
2007
105
2008
102
2009
101
2010
101
2011
101
11
9
6
3
3
3
12%
9%
6%
3%
3%
3%
Misclassification Rates
The survey VOD-K does not monitor the correctness of the classification of units in a certain
classification; therefore misclassification rates cannot be calculated.
Measurement Errors
Editing Rate
The editing rate is the ratio between the number of units for which the initially submitted data
had to be corrected and the number of all the units that submitted their replies.
The records on data editing are kept according to the number of units for which some of the
submitted data had to be corrected, whereas the records on the corrections of the key variables
are not kept and maintained. In 2011, during the first control phase of the questionnaires
VOD-K, 24 % missing data was acquired by phone, e-mail and telefax. Having received all
the complete questionnaires, the data editing rate during the control phase was 48 %
Prior to entry of the data in the computer database, all the questionnaires are ultimately
verified and the majority of data is edited.
3
Timeliness and Punctuality
3.1
Timeliness
Timeliness of the First Release
Timeliness of the first release of survey data is determined as the difference between the date
of the first release and the end of the reference period (in this case the last day of the year, to
which the data refer). The data on timeliness of the first release are presented in the table
below, in the form T+x, where T means the end of the reference period and x the number of
days.
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Table 3.1: Timeliness of the First Release
Reference period
31. 12. 2007 31. 12. 2008
Date of publishing 21. 8. 2008 10. 8. 2009
Time lag
T+233
T+222
31.12.2009
10.8.2010
T+222
31.12.2010
18.10.2011
T+291
31.12.2011
18. 10. 2012
T+292
Timeliness of Final Results
The data that are first published in the First Release are final data. Simultaneously they are
published also in the SI-STAT database.
3.2
Punctuality
Punctuality of the First Release
Punctuality of the first release of data is calculated as the difference between the announced
and the actual date of publication.
Table 3.2: Punctuality of the First Release
Reference period 31. 12. 2007 31. 12. 2008 31.12.2009 31.12.2010 31.12.2011
Announced date 21. 8. 2008 10. 8. 2009 10.8.2010 18.10.2011 18. 10. 2012
Publishing date
21. 8. 2008 10. 8. 2009 10.8.2010 18.10.2011 18. 10. 2012
Difference
0
0
0
0
0
4
Accessibility and Clarity
4.1
Accessibility
Channels used for the dissemination of the results
Table 4.1: Dissemination channels
No.: Channel
1
Web Site
Ad hoc prepared data for users according to their
2
specification
3
Digital media (data on diskettes, CD ...)
4
Data, available through telephone answering machine
5
Data presented at the News Conference
6
General printed publications
7
Thematic printed publications
8
Data bases (e.g. Social Science Data Archives )
9
Statistically protected micro data
Used
YES
YES
NO
NO
NO
YES
YES
NO
NO
Rate of Used Channels
The share of used channels was 44, 4 %.
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Means used for the dissemination of the results
Table 4.2: Means of dissemination
No.:
Mean
1.1
SORS Web Site
Web Sites of the institutions within the Slovene
1.2
statistical system
Data bases, accessible through internet (SDB, SISTAT –
1.3
PC AXIS)
1.4
Web Sites of international organisations
1.5
Thematic Web Sites (e.g. Census 2002)
2.1
Written requests
2.2
Telephone requests
3.1
CD, diskettes, disks
3.2
Mediation of data via the net (e-mail, protocols)
4.1
Data, available from the telephone answering machine
5.1
Data, presented at the News Conference
6.1
Yearbook
6.2
Slovenia in Figures
6.3
Some Important Data on the Republic of Slovenia
7.1
First Release
7.2
Rapid Reports
7.3
Results of Surveys
Special (e.g. Review on transport movements) and
occasional (e.g. Censuses in Slovenia 1948-1991)
7.4
publications
7.5
Eurostat publications
Publications of other international organisations (OECD,
7.6
IMF)
8.1
Data bases, intended for internal use at SORS
Bases, accessible also to other users than those within
8.2
SORS
Used
YES
NO
YES
NO
NO
NO
NO
NO
NO
NO
NO
YES
YES
YES
YES
NO
NO
NO
YES
NO
NO
NO
Rate of Means Used
The share of used dissemination means amounted to 32 %.
4.2
Clarity
Results Presented
The survey results were presented as absolute figures.
Level (Detail) of Presentation
Due to confidentiality, survey results are disseminated at the national level only. On the
SORS website (in the SI-STAT data portal, subject area Environment, area Water, subarea
Public savage network) there are the following tables for Slovenia:
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-
Waste water generated by source of pollution (1000 m3)
Waste water by level of treatment (1000 m3)
Waste water discharged by water sources (1000 m3)
Waste water by hydrographic basins (1000 m3)
Sewage system, connections to the sewage system and street gutters.
5
Comparability
5.1
Comparability over Time
Length of Comparable Time Series
Comparable time series are available from 2003.
Breaks in Time Series
The beginning of the sewage system survey dates back to 1982, when the SORS started with
the collection of the sewage system data, then entitled VOD-2K. Until 1992 data processing
was run without the assistance of computers: in the summary tables, data were calculated
manually. In that period the comparability of data and the methodology were often changed.
Survey data are thus accessible from 1993 on. In 2001 the survey was given its current title:
VOD-K. Due to the diminishing of the administrative burden related to the collection of data
for statistical purposes, the survey was entirely renewed in 2003. The VOD-K questionnaire
was changed both visually and contents-wise. The contents of all the tables were defined
anew. Due to rationalisation of data collection, the table on the capacity of the treatment plant
for treatment of the sewage waste water was omitted, as these data were monitored by the
Environmental Agency of the Republic of Slovenia. The table on use of mud from the
treatment plants was also omitted, as the data were monitored by the statistical survey in the
field of water (VOD-UVI). In order to acquire data on the level of development of the sewage
system infrastructure, a table was introduced containing a list of the municipalities and
settlements connected to the sewage system. The 2003 review of the questionnaire thus
contributed to diminishing the burden of the reporting units, as some of the questions were
omitted and also the number of the tables to be completed diminished from 7 to 5. Therefore
the time series can be observed in detail from 2003 on.
5.2
Geographical Comparability
Comparability with Other Members of the European Statistical System
As the majority of EU Member States, SORS also collects data on public sewage with a
special annual survey. Survey results are comparable to those of similar surveys on the public
sewage system conducted by other EU Member States, as they are required to complete the
joint EOCD/Eurostat questionnaire on inland waters; part of this questionnaire relates also to
formation and release of waste water from the public sewage system. The basis for
submission of data in the said questionnaire is based on the Decision No 2367/2002/EC of the
European parliament and of the Council of 16 December 2002 on the Community statistical
programme 2003 to 2007.
5.3
Seasonal Adjustment
This survey does not use the seasonal adjustment method.
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6
Coherence
6.1
Coherence between Provisional and Final Data
Coherence between Provisional and Final Data
Provisional data are not disseminated.
6.2
Coherence with the Results of the Reference Survey
Reference Survey
There is no similar survey, thus there is no source for comparison and the data cannot be
compared.
Coherence with Reference Data
See 6.2.1.
7
Costs and Burdens
7.1
Survey Costs of the Office
Table 1: Survey costs at the Statistical Office
Number of working hours spent
Number of reporting units that had to fill questionnaires
Period
Number of questionnaires (total)
265
101
annual
304
Comments: In calculating the costs of the Office for carrying out the survey, only the costs
arising from the number of working hours spent by the Office’s workers are considered.
7.2
Costs and Burden of Reporting Units
The average amount of time spent by a reporting unit to complete the questionnaire VOD-K
was estimated on the basis of a survey, conducted among the small, medium-size and large
reporting units. It revealed that a reporting unit spends on average 14 hours per year to acquire
and fill in the data that are collected with the VOD-K questionnaire.
Table 2: Burden and costs of the reporting units
Number of reporting units
that submitted their data
Annual number of
questionnaires per unit
Time spent to fill in a
questionnaire (hours)
Total time spent
(hours)
98
31
14
2881
Comments: Average time spent by the reporting unit to complete the questionnaire VOD-K
was estimated with a survey for selected small, medium and large reporting units. Reporting
1
If the manager of the sewage manages several sewage systems in the municipality or in several municipalities,
a questionnaire has to be filled in for each sewage system.
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unit spent an average 14 hours per year to obtain and enter the data we gather by a
questionnaire VOD-K.
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