Selection Bias in Web Surveys and the Use of Propensity Scores
The most obvious potential drawback of web surveys is that they may not be representative of the population of interest because the sub-population with access to Internet is quite specific. In Selection Bias in Web Surveys and the Use of Propensity Scores (SSRN) (RAND Working Paper No. WR-279) the authors investigate propensity scores as a method for dealing with selection bias in web surveys.
Findings. The propensity adjustment works well for many but not all variables investigated. For example, they find that correcting on the basis of socio-economic status by using education level and personal income is not enough to get a representative estimate of stock ownership. This casts some doubt on the common procedure to use a few basic variables to blindly correct for selectivity in convenience samples drawn over the Internet. Alternatives include providing non-Internet users with access to the Web or conducting web surveys in the context of mixed mode surveys.
See also: Are 'Webographic' or Attitudinal Questions Useful for Adjusting Estimates from Web Surveys Using Propensity Scoring? (SSRN)(RAND Working Paper Series No. WR-506). [JH]
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