In this database, domestic employment, labour volume (hours worked) and the wage costs of wage earners are broken down per industry (A38 of Nace rev. 2) according to gender, age group and education level. The breakdowns of employment and labour volumes are available for domestic employment as a whole and for wage earners and self-employed people separately. The database provides annual results for the period 1999-2018 and corresponds with the last edition of the national accounts (October 2019).
The methodology used still corresponds broadly with the one described in Working Paper 02-07 of the Federal Planning Bureau  apart from the fact that, besides persons employed, labour volumes and wage costs  are now processed this way as well. For estimating wage costs by education level, a new methodology was developed.
The industry totals per status (wage earners/self-employed) in the last edition of the national accounts (October 2019) are the starting point for the database. In a first stage, these figures are further broken down using administrative data from social security institutions . Thus, for wage earners, the number of persons employed, the labour volume and the wage costs per national accounts industry are split according to gender, age group, sub-status (blue collar workers, white collar workers and civil servants) and working-time regime (full-time and part-time workers) on the basis of social security data. For the self-employed, the number of persons employed per national accounts industry is split according to gender, age class and sub-status (self-employed in the strict sense, paid and non-paid assistants).
The social security data are merged with the NBB’s company register at the firm/institution level, which guarantees a match with the industry classification used in the national accounts. Furthermore, raw social security data are cleaned of time series breaks as much as possible and where possible adjusted to concepts that are commonly used in the national accounts. Every remaining discrepancy with the national accounts is removed by proportionally raising the figures to the industry totals of the national accounts.
In a second stage, breakdowns that are not available in administrative data are generated by using survey data. For example, the labour force survey (LFS) was used to break down the labour volumes of the self-employed according to age group and gender. The split of persons employed and labour volumes according to education level was also based on this survey, both for wage earners and self-employed.
The LFS is a survey among 1% of the working age population. Regression techniques, not averages, were used to get stable results for all subgroups. The number of persons employed per education level was assessed through logistic regression. The labour volume of the self-employed and the average labour volume per education level were assessed by using OLS.
All estimates were made separately per gender and A38-industry for four sub-statuses (blue collar workers, white collar workers, civil servants & contract workers, self-employed & assistants) and for six large age groups (15-19,20-24,25-39,40-49,50-59,60+). When there was a lack of observations, subgroups were merged.
Finally, the wage costs of wage earners were broken down according to the highest education level attained. The education levels concerned are primary or lower secondary education, higher secondary education, higher short-type education, and higher long-type or university education. The calculation, made in two steps, was based mainly on the Wage Structure and Distribution Survey.
First, the gross wages of wage earners by industry were detailed by combining the previously calculated labour volumes with education level premiums. These education level premiums for gross wages were estimated using the results of the Wage Structure and Distribution Survey for the 2000-2017 period. By using regression techniques, annual education level premiums could also be generated for a number of industries that were polled only every four years in the survey , as well as education level premiums for the years 1999 and 2018.
In a second stage, wage costs based on previously determined totals per gender, age group, industry, working-time regime and sub-status of wage earners were proportionally split between education levels according to the breakdown of gross wages. Since employers’ contributions in Belgium are proportionally lower for lower gross wages , the wage cost of the less qualified is overestimated. However, the global overestimate is limited due to the level of detail of the calculations. Indeed, the breakdowns of wage costs that were calculated using administrative data are fully respected.
Three industries are not incorporated in the Wage Survey: Agriculture, forestry and fishing (A), Public administration and defence; compulsory social security (O) and Activities of households as employers (T). Education level premiums were calculated for the net wages in these industries in LFS data. As regards the industry Public administration and defence; compulsory social security (O), which gave work to 11.1% of wage earners in 2015, an additional adjustment was made for the conversion of net wages into gross wages. This adjustment is based on the net/gross wages ratios for comparable subgroups within the industry Education (P).
The database does not yet contain any breakdown of the mixed income of self-employed people per gender, age class or education level.
 The National Social Security Office (NSSO), the National Social Security Office for Provincial and Local Public Services, and the National Institute for the Social Security of the Self-Employed (NISSE).
 Bresseleers, e.a. Kwalitatieve werkgelegenheidsdata voor België, een SAM-aanpak voor de periode 1999-2005. Working Paper 02-07, Federal Planning Bureau, 2007.
 A bottom-up approach is followed for wage costs. Totals per industry for different components of wage costs (gross wages; employers’ social contributions) are broken down separately using administrative data. The results for the wage costs follow from aggregation.
 As regards the industries Education (P), Human health activities (QA), Social work activities (QB), Arts, entertainment and recreation (R) and part of Other service activities (S), the Wage Structure and Distribution Survey has observations for the years 2006, 2010 and 2014 only.
 The employer’s contribution is a fixed percentage of the gross wage, from which a “structural reduction” is deducted. This structural reduction is higher for the lowest and (to a lesser extent) the highest wages. Social security contributions reductions for specific target groups (such as less qualified, younger or older wage earners) are regarded as wage subsidies in the ESA2010. They are not deducted from employers’ social contributions but are part of the other subsidies on production in the national accounts. Therefore, social security contributions reductions for target groups have no impact on wage costs in the Qualitative employment data of 1999-2018.