Expected number of secondary cases versus number of contacts. The boxplots show the distribution of the expected number of secondary cases that are induced by one infector that is introduced into a fully susceptible population. The values are grouped by the number of contact partners of the infectors. The boxes represent the interquartile range (IQR) with the median values marked as horizontal line. The whiskers are defined as max. ± 1.5·IQR. Circles are outliers and asterisks are extreme outliers. The subfigures represent the following basic reproduction numbers: a) R0 = 1.5; b) R0 = 3.0; c) R0 = 4.5; d) R0 = 6.0. Subfigures a-c are cropped such that one outlier lies outside the displayed range. The corresponding person day had 28 reported contacts and amounts SC = 14.15 for subfigure a, SC = 24.00 for b, and SC = 27.76 for c. The rationale for this outlier is presumably a reporting bias from the participant; i.e., the participant stated that she or he had close contact lasting for hours with a large number of persons at a festivity. Interacting closely with a large number of persons at a festivity over long time is almost impossible when the rigid contact definition in the diary is used.