“…For example, students with high grade point averages are more likely to participate in surveys and are better reporters of their grade point average than low grade point average students, even in studies where the topic is not academic achievement (Olson, 2007; Olson and Kennedy, 2006). Demographic characteristics of the sampled person such as education, age or sex are other ‘personal characteristics’ that may be related to both a person's response propensity and quality of data (Armenakis and Lett, 1982; Cannell and Fowler, 1963; Kaminska et al ., 2006; Mason et al. , 2002; Olson, 2006; Olson and Kennedy, 2006; Safir and Tan, 2009).…”