An intervention program designed by the Stockholm Transit District was implemented to improve the work conditions of the city’s bus drivers. Improvements were evaluated by G. Evans et al., who collected physiological and psychological data for bus drivers who drove on the improved routes (intervention) and for drivers who were assigned the normal routes (control). Their findings were published in the article “Hassles on the Job: A Study of a Job Intervention with Urban Bus Drivers” Following are data, based on the results of the study, for the heart rates, in beats per minute, of the intervention and control drivers.a. At the 5% significance level, do the data provide sufficient evidence to conclude that the intervention program reduces mean heart rate of urban bus drivers in Stockholm?

b. Can you provide an explanation for the somewhat surprising results of the study?

c. Is the study a designed experiment or an observational study? Explain your answer.

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Intervention 68 74 69 68 64 66 58 63 73 76 74 52 77 53 60 77 Control 67 63 76 63 66 71 66 55 63 73 59 77 57 73 54 68 64 71 84 68 64 82 54 60 80