Several quantitative variables were recorded for each in a sample of 28 geography journals: cost of a 1-year subscription (dollars); Journal Impact Factor (JIF) - the average number of times articles from the journal have been cited; number of citations for the journal over the past 5 years; and Relative Price Index (RPI). The data for the 28 journals are saved in the file. (Selected observations are listed below.)

a. Fit a straight-line model relating cost (y) to JIF (x). Find an estimate of σ, the standard deviation of the error term, and interpret its value.
b. Fit a straight-line model relating cost (y) to number of citations (x). Find an estimate of σ, the standard deviation of the error term, and interpret its value.
c. Fit a straight-line model relating cost (y) to RPI (x). Find an estimate of σ, the standard deviation of the error term, and interpret its value.
d. Which predictor of cost-JIF, number of citations, or RPI-leads to a regression line with the smallest errors of prediction?
For Information: Refer to the Geoforum (Vol. 37. 2006) study of whether the price of a geography journal is correlated with quality. Exercise 2.127.

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Journal Cost (S) JIF Cites RPI I. Econ. Geogr. Prog. Hum. Geog. T. I. Brit. Geogr Econ. Geogr. A. A. A Geogr. Geogr. Anal. Geogr. J Appl. Geogr 468 624 90 2.388 544 116 1.11 499 2.325 31 0.88 0.902377 0.30 81 0.94 74 3.38 3252490.77 698 213 223 646 2.1153770.93 0.902 106 0.88 0.857 0.853