The bad news is that only 77% of men regularly wash their hands after using a public restroom (93% of women do so). The good news is that according to Maria Knight Lapinski from Michigan State University and her colleagues from the University of Pennsylvania, West Chester University and North Central College, those numbers can be improved upon with a little messaging.
The researchers observed the hand-washing behavior of 252 men who entered a university bathroom alone. Confederates outside the bathroom prevented other men from entering and disrupting the experiment by hanging ‘Out of Order’ signs on the door. Inside the bathroom, each subject was presented with one of six different combinations of messaging and privacy. Posters on the walls indicated either that four out of five students wash their hands after using the restroom (high prevalence) or that only one out of five do so (low prevalence). There was also a no poster control. Some of the time, the observer was hidden (private), whereas in other tests the observer was clearly visible (public). To be clear, in either case, the observer was watching the sinks, not the stalls or urinals so it wasn't at all creepy.
The observers noted both whether or not the subject washed his hands at all (liquid hitting the subject’s hands for one or more seconds was counted as a ‘yes’) and how thorough the washing had been (duration, use of soap, etc).
Interestingly, 88% of men who saw the low prevalence posters washed their hands, but only 81% of men in bathrooms with high prevalence posters washed their hands. Either poster was better than nothing, because only 70% of the men who weren’t exposed to any of the posters washed their hands. The no poster group also washed for one third less time than the people who saw posters (though almost everyone fell well short of CDC guidelines). The men were more virtuous when they thought someone might be watching. 86% washed in front of a visible observer whereas only 75% washed when they thought they were alone.
Putting up posters is a lot less expensive, not to say antagonistic, than installing sink monitors in every public restroom. The tactic also seems to be surprisingly effective. When queried, male college students believe that only about half their cohorts regularly wash their hands after using the bathroom, even though they themselves do wash their hands. Apparently, hygiene posters remind people to continue using good bathroom practices.