Before purchasing videoconferencing equipment, a company tested its current internal computer network. The tests measured how rapidly data moved through its network given the current demand on the network. Eighty files ranging in size from 20 to 100 megabytes (MB) were transmitted over the network at various times of day, and the time to send the fles (in seconds) recorded. The time is given as the number of hours past 8 A.M. on the day of the test.
(a) Fit the multiple regression of Transfer Time on File Size and Hours past 8. Does the model, taken collectively, explain statistically significant variation in transfer time?
(b) Does either explanatory variable improve the ft of the model that uses the other? Use a test statistic for each.
(c) Find the variance inflation factors for both explanatory variables. Interpret the values that you obtain.
(d) Can collinearity explain the paradoxical results found in parts (a) and (b)?
(e) Would it have been possible to obtain data in this situation in a manner that would have avoided the effects of collinearity?