Question: Injuries are common in football and may be related to a number of factors, including the type of playing surface, the number of years of playing experience, and whether any previous injury exists. A study of factors affecting injury among Canadian football players was recently reported.

The rate of injury to the upper extremity [that is, shoulder to hand] on a dry field consisting of natural grass is 2.73 injuries per 1000 games. Assume this rate is known without error.

The study reported 45 injuries to the upper extremity on a dry field consisting of artificial turf among 10,112 games. What procedure can be used to assess if the risk of injury is different on artificial turf versus natural grass?