Combining Information from Web Based Survey and Telephone Survey

An on-line survey on the Internet, a web survey, is a new way of collecting data from the users of a web site. However, if answering is voluntary, a low response rate can be expected, and an analysis based on the observed data alone may give biased and misleading results due to self selection. The research question we address in this paper is; what solutions can be recommended to correct for the possible bias due to non-response? Our suggestion is to perform an additional survey, with better quality with respect to the response rate and self selection bias, to combine the two surveys by statistical modelling. This approach is used to study a specific web site, where data were collected both by web and telephone surveys.