What is volunteer bias?
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Volunteer bias can be defined as the bias that comes from the fact that a particular sample can contain only those participants who are actually willing to participate in the study or experiment (Heiman, 2002). There are apparent differences between those people who are willing to participate in a study or experiment and those who do not wish to do so. According to Heiman (2002), volunteers tend to have a higher social status and intelligence, exhibits an increased need for approval, and have a tendency to be less authoritarian and conforming. Also, those who participate and find the topic particularly interesting are more likely to volunteer for that study, same to those who are expected to be evaluated on a positive level (Heiman, 2002).
Example / Application
Application: Surveys are very prone to contain volunteer bias. Those who are not willing to participate have a particular attitude or characteristics (e.g., especially busy or laziness). Those who are willing to participate have a different type of attitude toward a survey (e.g., inactivity or bored) (Heiman, 2002). Some research has found that more motivated participants do give better data to certain kinds of questions (Chang & Krosnick, 2009) due to less 'satsficing' which is the practice of giving any answer to satisfy the questionner.
Heiman, G. W., (2002). Research Methods in Psychology. 3rd Edition. Boston & New York. Houghton Mifflin Company.
Also see: Robert Rosenthal and Ralph L. Rosnow (1975), The Volunteer Subject, which reviewed and summarized the copious research up until that time. Their book appeared in the Wiley Series on Personality Processes (John Wiley & Sons, New York).
Chang & Krosnick (2009). "National Surveys Via Rdd Telephone Interviewing Versus the Internet Comparing Sample Representativeness and Response Quality" Public Opin Q (2009) 73 (4): 641-678.doi: 10.1093/poq/nfp075 First published online: December 1, 2009