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Accuracy and reliability

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Prices and Consumption, Economic Statistics
Peter Fink-Jensen
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Cost index for refuse collection, sludge removal and freight transport by road

Index weights are established in cooperation with Dansk Transport og Logistik (the Danish Transport and Logistics Association) and Dansk Industri (Confederation of Danish Industry). The indices are deemed representative for refuse collection, slurry pump and freight transport by road performed in Denmark.

Overall accuracy

The quality of data collection and weight basis is continuously monitored. The index is considered to be of high quality, and representative of the general development of costs associated with refuse collection, slurry pump and freight transport by road in Denmark.

Sources of error include faulty price reporting by companies, and the accuracy of the weight basis used to represent contemporary work with refuse collection, slurry pump and freight transport by road in Denmark, which may change over time. This is accommodated by continuous monitoring of prices and data validation, as well as updates of the weight basis approximately every five years.

Figures on the statistical reliability are not estimated.

Sampling error

Some prices are collected from the Price index for Domestic Supply, which selects reporting companies using a "top-down" principle based on company turnover. Other price sources are selected based on data quality and availability. As the data sources have not been randomly selected, an estimation of sampling error cannot be performed.

Non-sampling error

Errors related to price reporting: The index is calculated based on a fixed basket of goods. In reality, goods may be substituted. This may cause discrepancies between price developments in the index and what is actually experienced by companies. This is uncertainty is minimized by running error sampling, quality control and contact with companies. Errors may occur when an enterprises report prices for other commodities than expected. The reason for this is normally misunderstandings e.g. change in staff. Such errors are sought to be minimized by continuous random sampling of prices, as well as dialogue with companies, which are requested to evaluate the validity of their reported wares approximately every two years.

The population sample for Price index for Domestic Supply covers minimum 70 percent of Danish production and import, and is therefore considered to be representative of the actual price development in the population.

Other uncertainties: Changes in the salary agreements often take effect from the month of March. The new agreements, however, are often not publicly available until the second quarter. Thus, they are not included until the calculation of the second quarter. This might produce a slight discrepancy between when the agreement actually take effect and when this effect shows up in the development of the indices.

Errors may occur when questionnaires are recorded in Statistics Denmark. Our error checking procedures normally spot such errors, so recording errors are not regarded to be important. Calculations are performed by routine computer programming, and errors are therefore not considered to occur in that context.

Index calculations are performed in a dedicated calculation software system. The probability of calculation errors is therefore considered to be insignificant.

Quality management

Statistics Denmark follows the recommendations on organisation and management of quality given in the Code of Practice for European Statistics (CoP) and the implementation guidelines given in the Quality Assurance Framework of the European Statistical System (QAF). A Working Group on Quality and a central quality assurance function have been established to continuously carry through control of products and processes.

Quality assurance

Statistics Denmark follows the principles in the Code of Practice for European Statistics (CoP) and uses the Quality Assurance Framework of the European Statistical System (QAF) for the implementation of the principles. This involves continuous decentralized and central control of products and processes based on documentation following international standards. The central quality assurance function reports to the Working Group on Quality. Reports include suggestions for improvement that are assessed, decided and subsequently implemented.

Quality assessment

Overall the Cost index for refuse collection, slurry pump and freight transport by road is assessed to be of high quality and representative of price developments in these industries.

It is not possible to determine a measurement of errors in the index. Coverage and measurement errors may occur if the quality of reported goods changes, or if reporting companies report prices of the wrong goods and services.

To accommodate this, data quality is continuously monitored. Quality upgrades may include increased sampling of new companies, an increase in reported prices by existing companies, or the use of different methods to define and calculate prices. Running dialogue with reporting companies also decrease misunderstandings and faulty reporting.

Data revision - policy

Statistics Denmark revises published figures in accordance with the Revision Policy for Statistics Denmark. The common procedures and principles of the Revision Policy are for some statistics supplemented by a specific revision practice.

Data revision practice

Only final figures are compiled.