Accuracy and reliability

Overall accuracy

The ability of the statistics for cooperative housing to precisely describe the true price development depends on model assumptions and the uncertainty of the date sources.

The price development for cooperative housing units is calculated using a hedonic regression where there is limited information on the individual cooperative housing units and the associated cooperative housing association. Using this method the price is modeled as a function of e.g. size, age and geographical location as well as information on the association.

For the period 2015Q1 - 2021Q2 the statistics is not revised as no new data is collected for this period.

Sampling error

For the period 2021Q3 and onwards the survey is based on mandatory reports from andelsboliginfo.dk and thus, there is no sampling error.

For the period 2015Q1 - 2021Q2 the statistics is based on a voluntary survey and some sampling error is to be expected. The development in the valuation principles is assessed to be accurate.

Non-sampling error

Some reports on andelsboliginfo.dk may be reports of previous sales but with slightly different data. These duplicates are identified and only the sale with the most accurate data is kept for the calculation. Duplicates are when two or more sales with identical addresses have sales dates within 30 days of each other. In total 0,6 pct. of the reported sales are duplicates.

The reported data can be erroneous, as very little data validation is carried out at andelsboliginfo.dk, The purpose of the website is to support the cooperative housing associations' obligation to report at transfers of cooperative housing units. It is the cooperative housing associations' responsibility that the key figures are correctly calculated and reported. The data belongs to the cooperative housing associations and they are responsible for the data quality. When Statistics Denmark receive the data from andelsboliginfo.dk extensive controls are carried out on the information to be used in the statistics for cooperative housing. 11 essential variables have been selected to receive the most attention.

The address (e.g. street name and postal code) along with the cooperative housing associations' central business register ID can be reported erroneously with can cause problem when connecting the sales information with the association information and information from the Dwellings and Buildings Register. Thus, these sales will not be included in the calculation of the price index. This presents an element of error on the calculated price development in comparison to the actual price development.

For the period 2021Q3 and onwards the data comes from mandatory reports through andelsboliginfo.dk. It is possible that some sales are not reported or they may reported too late to be included in the calculation of the most recent quarter.

The price index for cooperative housing units is calculated as a hedonic priceindeks using a rolling time dummy (RTD). This method assumes that the coefficients for the different characteristics are unchanged in four consecutive quarters. When the prices of the characteristics are limited to being unchanged, the quality adjusted price development between two periods is caught by a time dummy that takes on the value 0 i period 1 and 1 in period 2.

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

The calculation of the price index for cooperative housing units is complicated by the fact that cooperative housing units with different characteristics are sold from quarter to quarter

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

Figures from the period 2015Q1 - 2021Q2 are final and will not be revised. Figures from the period 2021Q3 and onwards will be revised continuously.