2:58 PM Wed Jul 15 7:47 L81% Exit In 2013, researchers in Australia analyzed data from a random sample of bicycle accidents involving collisions with motor vehicles in New South Wales during 2001 2009. One of the variables the researchers analyzed is whether or not cyclists were wearing helmets. The table below includes count of head injuries compared to other, non-head injuries. In this table, the observed count appears above the expected count in each cell. Bicycle accidents in New South Wales, 2001 to 2009 Wearing helmet No helmet Total Head injury Other injury Total Observed 372 4715 5087 Expected 481.9 4605.1 Observed Expected 267 1391 1658 157.1 1500.9 639 6106 6745 Reference: Bambach, M.R., R.J. Mitchell, R.H. Grzebieta, and J. Olivier. 2013. The effectiveness of helmets in bicycle collisions with motor vehicles: A case control study. Accident Analysis and Prevention 53: 78-88. Researchers conducted a chi-square test of independence with this data. Chi-square test results: chi-square test statistic 112.7, P-value < 0.0001. What can the researchers conclude? There is no statistically significant association between wearing a bicycle helmet and head injury. Researchers have strong evidence that not wearing a bicycle helmet and the occurrence of head injury are independent. Nothing, because the conditions for use of the chi-square test are not met. Not wearing a bicycle helmet is associated with higher rate of head injury. The association is statistically significant.