Investigators are testing a hypothesis that occupational stress causes high blood pressure. Two major groups of employees are of interest: bus drivers and office workers in the same salary range. The investigators measure the blood pressure of bus drivers from a bus-driving company and of office workers in the same salary range. The mean blood pressure of the bus drivers is compared with the mean blood pressure of the office workers. What study design is applied here? Why do you think so? Give one strength and one limitation of this study design.