Question

Favorite search engine	Internet Explorer users	Firefox users	Other browser users	All users
Google	192	211	31	434
Bing	161	131	22	314
Other	27	18	7	52

Level A 28. A company that advertises on the Web wants to know which search engine its customers prefer as their primary search engine: Google or Bing. Specifically, the company wants to know whether the preference depends on the browser being used. The file P08_28.xlsx con- tains counts of 800 customers' favorite search engine, broken down by the browser used. a. Find a 95% confidence interval for the difference between two proportions: the proportion of Internet Explorer users whose favorite search engine is Google and the similar proportion of Firefox users Repeat part a, replacing Google with Bing. c. Interpret the results in parts a and b. Do the search engine preferences seem to depend on the browser used?

Explicitly using EXCEL (or STAT TOOLS), please do A & B.

Answer 1

(a) The Excel output is:

p1	p2	pc
0.5053	0.5845	0.5439	p (as decimal)
192/380	211/361	403/741	p (as fraction)
192.	211.	403.	X
380	361	741	n
	-0.0792	difference
	0.0366	std. error
	-0.1507	confidence interval 95.% lower
	-0.0077	confidence interval 95.% upper
	0.0715	margin of error

The 95% confidence interval for the difference between the two proportions is between -0.1507 and -0.0077.

(b) The Excel output is:

p1	p2	pc
0.4237	0.3629	0.3941	p (as decimal)
161/380	131/361	292/741	p (as fraction)
161.	131.	292.	X
380	361	741	n
	0.0608	difference
	0.0359	std. error
	-0.0094	confidence interval 95.% lower
	0.131	confidence interval 95.% upper
	0.0702	margin of error

The 95% confidence interval for the difference between the two proportions is between -0.0094 and 0.131.

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