3.8 Sample size
Sample size was calculated based on somewhat similar study done in Hanoi, Vietnam (Hung, Stevenson & Ivers, 2008) titled “Barriers to, and factors associated, with observed motorcycle helmet use in Vietnam”, whereby among other things, it looked at the proportion of commercial motorcyclists who wear helmets and their attitudes towards helmet wearing. It was found that 23.1% of motorcyclists were reported wearing helmets. The formula for sample size calculation was as follows (Kirkwood, 2003):