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Ivo Dinov
UCLA Statistics, Neurology, LONI, Math/PIC

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STAT 13 (1a, 1b, 1c)	*Introduction to Statistical Methods for the Life and Health Science*
Department of Statistics	Instructor: Ivo Dinov
Homework 2	Due Date: Wednesday, Oct. 20, 2004

Please, submit your homework right after lecture on the due date. See the HW submission rules. On the front page include the following header.

(HW_2_1) Backpacks are commonly seen in many places, especially university campuses, schools, shopping malls and airplanes. In 1997, a US consumer magazine conducted a study on backpacks. Some of the data from the study is reproduced in the table below. The price of the backpacks is to the nearest US dollar, volume is measured in cubic inches and number of books is the number of 5-inch by 7-inch by half-inch books that the backpack easily holds.

Calculate the average volume used per book (i.e. the volume divided by the number of books) for each backpack.
Following the guidelines for tabular presentation (Section 2.2.2 of the text), redraw the table with the information from (a) added to it. Note: Assume that we are primarily interested in the price of the backpacks.

Add averages to the table as appropriate.
You may use Stata to draw the table.

Use either SOCR, Excel or Stata to create three separate scatter plots – volume vs price, number of books vs. price and number of books vs volume. Print out the three plots. Note: Each axis of the plots should be appropriately labelled. If possible, try to print the three plots on one sheet of paper.
Write a short report (from 150 to 250 words) about the data. Your report should include a discussion on the data (comments on trends, problems or interesting features in the data and what other data could be collected to help consumers compare backpacks) and a recommendation for consumers (which backpack(s) do you recommend buying and why). Are we missing some factors that may effect our purchasing decision? If so, give examples.

Backpack Code	PM	MM	BL	DS	CM	MR	MP	RP	JC	CB	EW	EA
Price($)	38	40	50	48	35	35	45	50	35	95	40	40
Volume	1586	1810	2200	1874	1810	1950	1670	1500	1635	1102	1700	1500
Number of Books	41	45	46	52	48	49	49	40	73	38	49	51

(HW_2_2) Describe/Address the following terms in your own words:

Outlier
Skewed Distribution
Sampling and Non-sampling errors
Give two examples of each of the three basic ways for data collection (surveys, designed experiments and observational studies).

(HW_2_3) On Friday, June 25, 1993, Spartanburg Herald-Journal classified section listed 13 Honda Accords for sale. The ages of the vehicles are given below in years, and the advertised price of each vehicle is given below in thousands of dollars.

Age: x	0	1	1	1	2	3	4	5	5	9	11	12	12
Price: y	16.2	17.1	16.0	16.2	11.7	12.8	10.0	9.0	6.0	2.5	2.0	1.9	1.5

a. Construct a scatter plot of the paired data (Age vs. Price).
b. What does the scatter plot convey to you about the price of a vehicle in relation to its age?
c. If you were to draw a line showing the trend in the relationship you described in (b), what would be its direction as you move from left to right? What could you say about its slope?
d. Draw the line that you believe fits the data the best.

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