The report "Wireless Substitution: Early Re- lease of Estimates from the National Health Interview Survey" (Center for Disease Control, 2009) gave the following estimates of the percentage of homes in the United States that had only wireless phone service at 6-month intervals from June 2005 to December 2008.
Percent with Only
6 800 320
3 1190 420
Date Wireless Phone Service
2 1090 120
5 570 290
3.5 1215 285
2.5 1160 390
0 520 140
2.5 1120 330
1 240 120
3 650 180
1 1620 340
4 660 380
3 840 300
1.5 1050 490
3 1440 380
9 750 560
1 500 230
1.5 1200 370
2.5 1200 330
3 1250 330
0 1040 220
0 760 260
2.5 780 220
3 500 230
a. Construct a scatterplot using y = calories and x = fat. Does it look like there is a relationship between fat and calories? Is the relationship what you expected? Explain.
b. Construct a scatterplot using y = calories and x = sodium. Write a few sentences commenting on the difference between the relationship of calories to fat and calories to sodium.
June 2005 7.3
December 2005 8.4
June 2006 10.5
December 2006 12.8
June 2007 13.6
December 2007 15.8
June 2008 17.5
December 2008 20.2
Construct a time-series plot for these data and describe the trend in the percent of homes with only wireless phone service over time. Has the percent increased at a fairly steady rate?