4. A study of nonfatal occupational injuries in the United States found that about 31% of all injuries in the service sector involved the back. The National Institute for Occupational Safety and Health (NIOSH) recommended conducting a comprehensive ergonomics assessment of jobs and workstations. In response to this information, Mark Glassmeyer developed a unique ergonomic handcart to help eld service engineers be more productive and also to reduce back injuries from lifting parts and equipment during service calls. Using a sample of 382 eld service engineers who were provided with these carts, Mark collected the following data. Find 95% condence intervals for the difference in average call times and difference in proportion of back injuries. What conclusions would you reach? Year 1 (Without Cart) Year 2 (With Cart) Average call time 8.05 hours 7.84 hours Standard deviation call time 1.39 hours 1.34 hours Proportion of back injuries 0.018 0.01