A Spanish Continuous Volunteer Web Survey: Sample Bias, Weighting and Efficiency*

Abstract

Using micro data from a continuous volunteer web
survey (CVWS), the WageIndicator (WI), this paper
firstly analyses the type of bias that such a survey
method produces. Secondly, following a «modelbased
» approach, two alternative data weighting
methodologies are implemented. Thirdly, in order to
test whether weighting corrects the bias, thus
making it possible to obtain conclusions applicable to
the whole labour force, the efficiency of the weighting methodologies is evaluated. Since the WageIndicator
is a labour market oriented survey, weighting
efficiency is evaluated by calculating mean salaries,
inequality indices and salary regressions before and
after applying weights to WI data, and by comparing
the results obtained with those achieved using the
Structure of Earnings Survey (SES), a wage survey
run by the Spanish National Statistics Institute. It is
concluded that, after weighting, estimated statistics
and parameters move in the right direction.