An inevitable weakness with psychology research is that so much of it is conducted with people (usually students) who have volunteered. If certain kinds of people routinely opt out of research, it could mean our estimates of what is psychologically average or ‘normal’ are completely off the mark.
Bernd Marcus and Astrid Schūtz at Chemnitz University of Technology tried to find out if people who don’t participate in research have different personalities from people who do. They emailed 685 people, mostly men, who maintained personal web-sites, asking them to participate in an “online study on psychological aspects of personal web pages”. Two hundred and eighty of them agreed to participate.
Over a hundred students, mostly women, then viewed the web-sites of people who had and hadn’t agreed to participate. Without knowing who had volunteered, the students used a web-site’s content to score its owner’s personality on things like sociability, anxiousness, creativity, intelligence, meticulousness and self-adoration – adjectives chosen to tap into the ‘Big Five’ personality factors of neuroticism, extraversion, agreeableness, openness to experience and conscientiousness.
People who volunteered to participate were rated as more agreeable and more open to experience than those who did not volunteer, even though the student raters were unaware of who had and hadn’t volunteered. “To the degree that these ratings are valid, these differences will translate directly into incorrect normative data in personality assessment”, the authors said. Therefore “…a finding that the sample mean in a given study does not deviate from published norms only applies to volunteers and does not generalise to the full population”, they warned.
Marcus, B. & Schūtz, A. (2005). Who are the people reluctant to participate in research? Personality correlates of four different types of nonresponse as inferred from self- and observer ratings. Journal of Personality, 73, 959-984.