The statistics has been compiled since 1995, but it can be problems in comparing figures over time. The questionnaire, the sample design and the calculation method have been adjusted a few time, latest in 2017.
To Eurostat the data are provided only for enterprises with less 20 person employed (according to EU's regulation). In the Statistics Database of Eurostat the distributions of the turnover by services and residence of client are published on EUROSTAT's homepage. It is considered that there are good comparability across countries, because the statistics should be produced by common guidelines and principles.
It can be problems in comparing figures over time. The survey was conducted for the first time in 1995. In relation to a pilot study in EU the questionnaire concerning 2001 has been revised which means that the results previous to 2001 are not totally comparable with the results concerning 2001 and forwards. The years 2005 and 2007 are not comparable because of a shift to NACE Rev. 2 activity classification. The years 2007 and 2009 are not comparable because of changes in the questionnaire. Products were adjusted to the EU questionnaire.
From the reference year 2013 the method is changed so the enumeration is based on a new data from the Central Business Register. That means the results before the year 2013 are not directly comparable to the results from 2013 onwards.
In Statistics Bank the data can be found back to 1995. Due to the differences in methods and units the data for the earlier years can't be expected to compare with the current data beginning with year 2013.
At national level the data for the survey are grossed up to the provisional turnover from the statistic Purchases and sales of enterprises ("VAT statistics"). The final turnover is not available at the time when data are grossed up. The VAT statistics provides the total turnover in the sector for Engineering Activities and Related Technical Consultancy, whereas this survey in addition to the total turnover also indicates the breakdown of the turnover by different services. At European level the data for the statistics are grossed up to the level for the Danish Accounts Statistics. As in the VAT statistics the breakdown of the turnover by various services doesn't exist in the accounts statistics but only in this survey.
Not relevant for these statistics.