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3.1 Paired data

Are textbooks actually cheaper online? Here we compare the price of textbooks at UCLA’s bookstore and prices at Amazon.com. Seventy-three UCLA courses were randomly sampled in Spring 2010, representing less than 10% of all UCLA courses.³⁰³⁰When a class had multiple books, only the most expensive text was considered. A portion of this data set is shown in Table 3.1.

	dept	course	ucla	amazon	diff
1	Am Ind	C170	27.67	27.95	-0.28
2	Anthro	9	40.59	31.14	9.45
3	Anthro	135T	31.68	32.00	-0.32
4	Anthro	191HB	16.00	11.52	4.48
$\vdots$	$\vdots$	$\vdots$	$\vdots$	$\vdots$	$\vdots$
72	Wom Std	M144	23.76	18.72	5.04
73	Wom Std	285	27.70	18.22	9.48

Table 3.1: Six cases of the textbooks data set.

3.1.1 Paired observations and samples

3.1.2 Inference for paired data