<p>12 monthly samples of 1,250 telephone numbers constitute the "incoming" fraction, with each unit surveyed for three consecutive months.</p>
<p>However certain households are not surveyed : impossibility to contact them, refusals... In general about 1,700 questionnaires are completed each month.</p>
<p>A methodological operation was carried out in April 2008 to measure the impact of survey base coverage bias.</p>
<p>The result was that the survey provides data of sufficient quality for short-term analyses.</p>
Datalift
