It seems to me that they fall into false positive - people visiting the site are most likely considering to change the job, that's what they are looking there f

It seems to me that they fall into false positive - people visiting the site are most likely considering to change the job, that's what they are looking there for. But how can they include in the poll the people who are happy at their current job and don't look for a new one (read, don't visit the job/recruitment site)? The survey doesn't seem to be representative.