Handbook of Web Surveys. Jelke Bethlehem

It should be advised that it is not possible to process non‐probability‐based survey data using statistical inference methods to estimate population. Comments about probability versus non‐probability‐based samples and the exclusive advantages of probability‐based samples are in Chapter 14.

      4 4 As stated above, if some units of the target population are not on Internet and/or an adequate online sampling list is available, alternative sampling frames could be available (for instance, ordinary mail addresses), and the sample could be drawn from this sampling list. In this case, sampled units that are not on the Internet could receive the invitation letter either by e‐mail or by ordinary mail.