2.30 Stopping traffic with a smile! Throughout Europe, more than 8000 pedestrians are killed each year in ro accidents, with approximately 25% of these dying when using a pedestrian crossing. Although failure to stop for pedestrians at a pedestrian crossing is a serious traffic offense in France, more than half of drivers do not sron when a pedestrian is waiting at a crosswalk. In this ex periment, a female research assistant was instructed to stand at a pedestrian crosswalk and stare at the driver's face as a car approached the crosswalk. In 400 trials, the research assistant maintained a neutral expression, and in a second set of 400 trials, the research assistant was instructed to smile. The order of smiling or not smiling was randomized, and several pedestrian crossings were used in a town on the coast in the west of France. Re- search assistants were dressed in normal attire for their age (jeans/T-shirt/trainers/sneakers).23 (a) In the 400 trials in which the assistant maintained a neutral expression, the driver stopped in 229 out of the 400 trials. Find a 95% confidence interval for the proportion of drivers who would stop when a neutral expression is maintained. p) In the 400 trials in which the assistant smiled at the driver, the driver stopped in 277 out of the 400 tri- als. Find a 95% confidence interval for the propor- tion of drivers who would stop when the assistant is smiling

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Chapter10: Statistics
Section10.6: Summarizing Categorical Data
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con
always be careful
about the relevant population.
accidents, with approximately 25% of these dying when
22.30 Stopping traffic with a smile! Throughout Europe,
more than 8000 pedestrians are killed each year in re
using a pedestrian crossing. Although failure to ston for
pedestrians at a pedestrian crossing is a serious traffic
offense in France, more than half of drivers do not srOn
when a pedestrian is waiting at a crosswalk. In this ev
periment, a female research assistant was instructed to
stand at a pedestrian crosswalk and stare at the driver's
face as a car approached the crosswalk. In 400 trials, the
research assistant maintained a neutral expression, and
in a second set of 400 trials, the research assistant was
instructed to smile. The order of smiling or not smiling
was randomized, and several pedestrian crossings were
used in a town on the coast in the west of France. Re-
search assistants were dressed in normal attire for their
age (jeans/T-shirt/trainers/sneakers).23
(a) In the 400 trials in which the assistant maintained
a neutral expression, the driver stopped in 229 out
of the 400 trials. Find a 95% confidence interval
for the proportion of drivers who would stop when
a neutral expression is maintained.
(b) In the 400 trials in which the assistant smiled at the
driver, the driver stopped in 277 out of the 400 tri-
als. Find a 95% confidence interval for the propor-
tion of drivers who would stop when the assistant
is smiling.
Transcribed Image Text:con always be careful about the relevant population. accidents, with approximately 25% of these dying when 22.30 Stopping traffic with a smile! Throughout Europe, more than 8000 pedestrians are killed each year in re using a pedestrian crossing. Although failure to ston for pedestrians at a pedestrian crossing is a serious traffic offense in France, more than half of drivers do not srOn when a pedestrian is waiting at a crosswalk. In this ev periment, a female research assistant was instructed to stand at a pedestrian crosswalk and stare at the driver's face as a car approached the crosswalk. In 400 trials, the research assistant maintained a neutral expression, and in a second set of 400 trials, the research assistant was instructed to smile. The order of smiling or not smiling was randomized, and several pedestrian crossings were used in a town on the coast in the west of France. Re- search assistants were dressed in normal attire for their age (jeans/T-shirt/trainers/sneakers).23 (a) In the 400 trials in which the assistant maintained a neutral expression, the driver stopped in 229 out of the 400 trials. Find a 95% confidence interval for the proportion of drivers who would stop when a neutral expression is maintained. (b) In the 400 trials in which the assistant smiled at the driver, the driver stopped in 277 out of the 400 tri- als. Find a 95% confidence interval for the propor- tion of drivers who would stop when the assistant is smiling.
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