One possible explanation for the variability in estimates across the different nonprobability samples is the range of methods that online sample vendors employ. They differ on recruitment, weighting ...

Non-probability Sample: A sampling approach that does not confer every population member a known probability of selection, often necessitating additional statistical adjustments.

This study reports the findings of a comparison between different non-probability sampling methods applied in a WWW-user-survey.

Web surveys can be conducted relatively fast and at relatively low cost. However, Web surveys are often conducted with nonprobability samples and, therefore, a major concern is generalizability. There ...