10.82 Stressed-Out Bus Drivers. An intervention program designed by the Stockhol
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Question
10.82 Stressed-Out Bus Drivers. 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 where published in the article "Hassles on the Job: A Study of a Job Intervention with Urban Drivers" (Journal of Organizational Behaviour, Vol. 20, pp. 199-208). 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? (Note: 1-67.90,s1 - 5.49,72-66.81, s2-9.04.) Page 1 of 2 Intervention 68 74 69 68 64 Control 58 63 73 76 74 52 67 63 77 57 80 77 53 76 54 73 54 60 77 63 60 68 64 66 71 66 55 71 84 63 73 5968 64 82 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 10.88 Stressed-Out Bus Drivers. Refer to Exercise 10.82 and find a 90% confidence interval for the difference between the mean heart rates of urban bus drivers in Stockholm in the two environments.Explanation / Answer
10.82
> intervention=c(68,66,74,58,69,63,68,73,64,76)
> control=c(74,52,67,63,77,57,80,77,53,76,54,73,54,60,77,63,60,68,64,66,71,66,55,71,84,63,73,59,68,64,82)
> mean(intervention)
[1] 67.9
> sd(intervention)
[1] 5.486347
> mean(control)
[1] 66.80645
> sd(control)
[1] 9.038508
a)
> t.test(intervention,control,alt="l")
Welch Two Sample t-test
data: intervention and control
t = 0.46025, df = 25.739, p-value = 0.6754
alternative hypothesis: true difference in means is less than 0
95 percent confidence interval:
-Inf 5.14759
sample estimates:
mean of x mean of y
67.90000 66.80645
Since p-value > 0.05, we accept the null hypothesis and conclude that there is no significant difference in mean heart rate of drivers under two environments.
b) There is not much difference in the sample means of the heart rates of two types of drivers and the pooled standard deviation is quite large.
c) This is a designed experiment since here the explanatory variables are intentionally changed and the value of the response is recorded.
10.88
> t.test(intervention,control,alt="l",conf.level=0.9)
Welch Two Sample t-test
data: intervention and control
t = 0.46025, df = 25.739, p-value = 0.6754
alternative hypothesis: true difference in means is less than 0
90 percent confidence interval:
-Inf 4.218729
sample estimates:
mean of x mean of y
67.90000 66.80645
> t.test(intervention,control,alt="g",conf.level=0.9)
Welch Two Sample t-test
data: intervention and control
t = 0.46025, df = 25.739, p-value = 0.3246
alternative hypothesis: true difference in means is greater than 0
90 percent confidence interval:
-2.031633 Inf
sample estimates:
mean of x mean of y
67.90000 66.80645
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