DataNet is an Internet service through which clients can find information and purchase various items such as airline tickets, stereo equipment, and listed stocks. DataNet has been in operation for four years. Data on monthly calls for service for the time that the company has been in business are in the data file called DataNet.
a. Plot these data in a time-series graph. Based on the graph, what time-series components are present in the data?
b. Develop the seasonal indexes for each month. Describe what the seasonal index for August means.
c. Fit a linear trend model to the deseasonalized data for months 1 through 48 and determine the MAD value. Comment on the adequacy of the linear trend model based on these measures of forecast error.
d. Provide a seasonally unadjusted forecast using the linear trend model for each month of the year.
e. Use the seasonal index values computed in part b to provide seasonal adjusted forecasts for months 49 through 52.