Accuracy and reliability
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Science, Technology and Culture, Business Statistics.Christian Törnfelt
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The statistics cover the majority of book sales in Denmark, purchased new. The metadata coverage is considered satisfactory for Danish publications, although coverage is lower for foreign publications. Coverage is also lower for books/book products where the primary purpose is not reading, such as coloring books, board books, activity books, calligraphy books, books with music notation, songbooks, and puzzle books like Sudoku. ISBN errors may occur, but they are not deemed to be a widespread issue.
The figures are preliminary, and future revisions may occur as book sales data expands and metadata quality improves.
Overall accuracy
The statistics cover the majority of book sales of Danish books, but not all. For example, sales of used books (antiquarians, second-hand stores, flea markets) or small independent bookstores and self-published books online are not included.
It is possible that an ISBN number has been registered incorrectly, either in the transaction data or on the Book Portal and/or Publizon. This could potentially result in books being categorized incorrectly in the statistics, but it is not considered to be a widespread issue.
Sampling error
Not relevant for this statistic.
Non-sampling error
The statistics do not cover the sale of used books, sales from small independent bookstores or self-published books online. Additionally, the metadata coverage is lower for foreign publications and certain types of hobby books, such as activity books and sheet music.
The statistics also do not include sales through streaming services, i.e., books purchased via subscription.
The statistics will continuously be expanded with additional sources and content. Efforts will be made to establish a robust data foundation on book streaming, with the aim of covering all forms of book sales in the market.
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 statistics are based on data from large booksellers and supermarket chains, as well as metadata from the two leading distribution platforms in Denmark. This ensures a high coverage of book sales in Denmark.
However, the statistics do not cover the sale of used books, sales from small independent bookstores or self-published books online.
The coverage is satisfactory for Danish publications but lower for foreign publications and certain types of hobby books. Since 2019, it has been mandatory for book releases to be registered with Thema codes on the Book Portal and Publizon. Therefore, it is expected that the quality of metadata for books published from 2019 onwards is higher than for publications released before 2019.
Future revisions of the figures may occur as metadata improves and data sources expand.
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
The figures are provisional, and future revisions may occur.