# What is the point estimate for p1-p2?

• December 7th 2011, 09:24 PM
Genevieve03
What is the point estimate for p1-p2?
Ok this is the last one I am struggling with. All of this is new to me just learned over the past few days but I really want to get it down. Any help will be appreciated. Thank you!

Kelly wanted to estimate the difference between the percentages of users of automobiles who would never change car brands. She took a sample of 500 users of Toyota (100 of who said they would never switch) and 400 users of Ford(68 of who said they would never switch).

A.) Let p1-p2 represent the two groups that use the above automobiles. What would the point estimate for p1-p2?
B.) Construct a 97% confidence interval for the difference between proportions of all users of the two automobiles who will never switch.
• December 7th 2011, 09:37 PM
pickslides
Re: What is the point estimate for p1-p2?
Try $\displaystyle p_1-p_2\pm Z_{0.97}\times \sqrt{\frac{p_1(1-p_1)}{n_1}+\frac{p_2(1-p_2)}{n_2}}$