Pew recently revisited the question of how survey modality can influence survey responses.  In particular, this survey used both web and telephone based surveys to ask participants about their attitudes towards politicians, perceptions of discrimination, and their satisfaction with life. As summarized in the article, the big differences are: "1)  People expressed more negative views of politicians in Web surveys than in phone surveys."  "2)  People who took phone surveys were more likely than those who took Web surveys to say that certain groups of people – such as gays and lesbians, Hispanics, and blacks – faced “a lot” of discrimination ."  "3)  People were more likely to say they are happy with their family and social life when asked by a person over the phone than when answering questions on the Web ."     The social psychologist in me likes this as an example of the Social Desirability Bias. When spea...