In: Statistics and Probability
Suppose that insurance companies did a survey. They randomly
surveyed 440 drivers and found that 330 claimed they always buckle
up. We are interested in the population proportion of drivers who
claim they always buckle up.
NOTE: If you are using a Student's t-distribution, you may
assume that the underlying population is normally distributed. (In
general, you must first prove that assumption, though.)
Construct a 95% confidence interval for the population proportion who claim they always buckle up.
(i) State the confidence interval. (Round your answers to four decimal places.)
,
(ii) Sketch the graph.
(iii) Calculate the error bound. (Round your answer to four decimal places.)
Solution:
(i) State the confidence interval.
Answer: The formula for finding the 95% confidence interval is:
Where:
is the sample proportion of drivers who always buckle up.
is the critical value at 0.05 significance level
is the sample size
Therefore, the confidence interval is:
Therefore, the 95% confidence interval estimate for the population proportion who claim they always buckle up is
(ii) Sketch the graph.
(iii) Calculate the error bound.
The error bound is: