Gerry Nicolaas (of Natcen) has just written a good review on the nonresponse workshop we both attended this year. See http://natcenblog.blogspot.com/2011/10/challenges-to-current-practice-of.html#comment-form The Nonresponse Workshops are a great place to meet and discuss with survey researchers in a small setting. The next workshop is to be held early september 2012 at Statistics Canada. See www.nonresponse.org
Mixed mode surveys have shown to attract different types of respondents. This may imply that they are succesful. Internet surveys attract the young and telephone surveys the old, so any combination of the two can lead to better population estimates for the variable you’re interested in. In other words, mixed-mode surveys can potentially ameliorate the problem that neither telephone, nor Internet surveys are able to cover the entire population.
The bad news is that mode-effects (see posts below) coincide with selection effect in mixed-mode surveys.
Mode effects - the fact that respondents respond differently to a survey question, solely because of the mode of interviewing - are hard to study. This is because mode-effects interact with nonresponse effects. An Internet survey will atract different respondents than a telephone survey. Because of this, any differences that result from this survey, could be either due to differences in the type of respondents, or because of a mode effect.
One of the most interesting issues in survey research is the mode effect. A mode effect can occur in mixed-mode surveys, where different questionnaire administration methods are combined. The reasons for mixing survey modes are multifold, but usually survey researchers mix modes to limit nonresponse, reach particular hard-to-reach types of respondents, or limit measurement error. It is more common today to mix modes than not mix them, for some good reasons: