Response rates and response bias. A common mistake in research is to evaluate a project s accuracy solely by the number of respondents in the study. Also important is the response rate what proportion of the people who you contact actually provide you answers. Mail surveys usually bring lower response rates, which means the study has a much higher chance of not truly representing the people it s supposed to. There is a much greater danger of this with mail than with telephone.
Response bias is a major part of the problem.
This means that one type of person is more likely to respond than another type of person. Good researchers balance for this type of response bias, or else the accuracy of the study is compromised. In some types of research, however, it s not possible to balance for this, particularly with a mail survey. This is why it s rarely a good idea to use a mail survey to test response to a new product concept, for instance. Let s say your organization is considering introducing a new service to donors, and you want to test donor response to the concept.