This document provides data on monthly bicycle-related head injury rates in percentages from January 2018 to December 2022 in Tasmania and Western Australia. It requires calculating the critical values and confidence intervals for the difference in mean injury rates between the two states/territories at the 95% and 75% confidence levels. Australia was the first country to mandate bicycle helmets and such legislation was introduced in Victoria in 1990 and other states/territories by 1992.