Question

A website reported that 28 % of drivers 18 and older admitted to texting while driving in 2009. In a random sample of 400 drivers 18 years and older drawn in 2010, 109 of the drivers said they texted while driving. Complete parts a through c below.

a. Construct a 90 % confidence interval to estimate the actual proportion of people who texted while driving in 2010.

A 90 % confidence interval to estimate the actual proportion has a lower limit of _ and an upper limit of _.

b. What is the margin of error for this sample?

c. Is there any evidence that this proportion has changed since 2009 based on this sample?

Because the confidence interval found in part a ___ the reported proportion from 2009, this sample ___ evidence that this proportion has changed since then.?

Answer 1

The statistical software output for this problem is:

One sample proportion summary confidence interval:
p : Proportion of successes
Method: Standard-Wald

90% confidence interval results:

Proportion	Count	Total	Sample Prop.	Std. Err.	L. Limit	U. Limit
p	109	400	0.2725	0.022262286	0.2358818	0.3091182

Hence,

a) 90% confidence interval:

Lower limit = 0.236

Upper limit = 0.309

b) Margin of error = (0.309 - 0.236)/2 = 0.0365

c) Contains; Do not provide