This is why the most cited whole-population studies have come from Australia and New Zealand where there was a quite sudden and dramatic increase in helmet usage as a result of well-publicized and enforced mandatory helmet laws. And there were traffic surveys conducted both before and in the years following the MHLs so that the numbers of fatalities and hospitalizations could be normalized based on changes in the number of riders. These studies have failed to find the hoped for benefits of increased helmet usage and even showed a slight increase in injury risk when the drop in ridership was taken into account.