ESENER-PSR 2009 - European Agency for Safety and Health at Work

example (see table 1.3.2.1.), a strictly establishment-proportional sample of 1.000 net
interviews would contain only 1,6% = 16 interviews in size-class 500+. These 16
interviews would on the other hand represent more than a quarter (27%) of all employees
within the defined universe. Such an analysis would be unacceptable.
Applying a strict employee proportional sample has its disadvantages and practical
limitations, too. In several smaller countries it would be practically impossible to meet the
requirements of a strict employee-proportional sample, since the absolute number of
establishments in the largest size-class is not sufficient for realizing a strictly employeeproportional
sample. As can be seen in this table, with a strict employee-proportional
sample in the example of Belgium about a third of all existing establishments (270 of 831)
of the size-class 500+ have to be interviewed 5 .
From practical points of view, such high shares of interviews in the largest size-classes
are not realistic. As response rates in these largest size-classes are certainly far from
100%, an employee-proportional sample would for several countries mean that practically
all establishments larger than 500 employees would have to be contacted. Since
especially the larger establishments are contacted very frequently for surveys of any kind,
their willingness to participate in surveys is often rather limited and should not be
overstressed, as this might lead to a general refusal of all kinds of surveys by this
important-sub-group. All address-providers and field-institutes therefore have a certain
(self-) interest in limiting the share of interviews in these largest size-classes. Apart from
that, in the chosen address-source not all of the large establishments might be listed. This
further restricts the possibilities of achieving the total number of interviews required for a
strict employee-proportional sample.
Another disadvantage of a strict employee-proportional sampling for this study is the fact
that for analysis both perspectives are important - employee-proportional and
establishment-proportional. A strictly employee-proportional sample would lead to
relatively homogeneous weighting factors for the employee-proportional weighting, but
would cause an extremely large variance of the weighting factors for the establishmentproportional
weighting - and vice versa. A large variance in the weighting factors has a
negative impact on the later analysis since it increases the risk that outliers have too much
influence on the findings.
Table 1.3.2.1:
Implications of employee- and establishment-proportional sample-designs at the example of
Belgium
Example Belgium
Number of interviews to be realized: 1.000
Size-class number % of all Cases number of % of all net cases
5 Belgium is not an exceptional case here. The ratio of the distribution of establishments and
employees is in most middle-sized countries comparable to the Belgian one. In smaller countries
which nevertheless have to produce a relatively high number of interviews, an even higher share of
the existing large establishments would have to be surveyed – in Austria e.g. 42%.
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