The interviews for the sample survey of industrial and service firms with 20 employees and over for the year 2008 were conducted in February and April 2009.
The sample consists of 2,901 non-construction industrial firms, 1,051 non-financial private service firms and 476 construction companies, representing 7.9, 3.6 and 6.0 per cent of their respective reference populations. The largest firms are over-sampled as this produces more accurate estimates of the totals of the main aggregates (employment, turnover, and investment) and of their fluctuations over a period of time. This imbalance is then taken into account during estimation. As a result of the bigger sampling fraction of large firms, the three samples account respectively for 27.9, 21 and 21.2 per cent of payroll employment in the reference populations; firms with 20 employees and over represent a substantial share of the sectoral aggregates.