In a study of driving practices in Strathcona County, Alberta, Canada, 48% of drivers were found not to stop at intersections with stop signs on county roads (Edmonton Journal, July 19, 2000) . Suppose a follow-up study conducted two months later found that 360 of 800 drivers did not stop at intersections with stop signs on county roads. Using the tools learned in the course, perform the required analysis assuming that the goal of the follow-up study is to see if the proportion of drivers who did not obey the stop sign changed, with a 2.5% margin of error.
Sample proportion = 360 / 800 = 0.45
With 2.5% margin of error,
confidence interval = - E < p < + E
0.45 - 0.025 < p < 0.45 + 0.025
0.425 < p < 0.475
Since 0.48 (Or 48% ) does not contained in confidence interval,
We have sufficient evidence to support the claim that the proportion of drivers who did not obey
the stop sign changed.
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