Fig. 2

Venn diagrams of the relationships across the three reasons mostly associated with (non)participation in a hypothetical health study among participants (a) and nonparticipants (b) of the influenza vaccination study. The data are based on the number of individuals who responded with “very important” or “important” to the questions on time demand and medical interventions, and “not important” or “not at all important” to the question on receiving health information (see Fig. 1, Table 2). Abbreviations: imp. = important; unimp. = unimportant