There are many factors that influence people's willingness to wear a mask. In a study by Tang and Wong [14] a total of 1,329 . The arrows that connect the boxed groups represent the movement of individuals from one group to an adjacent one. Nonmask wearing susceptible individuals (S) can either become exposed (E) or susceptible wearing a mask (S m ). Non-mask wearing exposed individuals (E) can either become infectious non-mask wearing (I) or mask wearing exposed (E m ). Non-mask wearing infectious individuals (I) can either recover (R), die (D), or become infectious wearing a mask (I m ). Mask wearing susceptible individual (S m ) can either become an exposed mask wearer (E m ) or a non-mask wearing susceptible (S). Mask wearing exposed individuals (E m ) can either become an infectious mask wearer (I m ) or a non-mask wearing exposed individual (E). A mask wearing infectious individual (I m ) can either recover (R), die (D), or stop wearing the mask while they are still infectious (I). doi:10.1371/journal.pone.0009018.g001