Fabo, B., & Kahanec, M. (2018). Can a voluntary web survey be useful beyond explorative research?, International Journal of Social Research Methodology, DOI: 10.1080/13645579.2018.1454639

In this paper, we compare the estimates of earnings determinants based on the non-probabilistic WageIndicator web survey with those based on the widely used, representative EU Study of Income and Living Conditions survey. Using 10 years of Dutch data, we show that there exists an established segment of predominantly junior workers from which the respondents of the WageIndicator survey are disproportionally drawn. In consequence, the composition of WageIndicator sample tends to retain key characteristics over the years, even though it lacks a probabilistic sampling frame. We show that the estimates produced on the basis of an extended Mincerian earnings model using the two data sources are qualitatively similar. In line with much of the literature, however, the two sets of estimates do not pass the formal statistical test of equality. Nonetheless, when we examine only the subsample of junior workers, the statistical testing does not detect a statistically significant difference between the two datasets in many instances. To our knowledge, ours is the first paper showing such statistical evidence for comparability of a web survey based with a widely used representative data source.