An online travel agency is performing market analysis to determine how their sales have impacted brick-and-mortar travel agencies in key cities since launch ten years ago.
The data contain the monthly number of airline tickets sold by a local travel agency in Grand Rapids, Michigan during the first four years of the online travel agency's business.
(A) Is this time series random? Perform a runs test and compute a few autocorrelations to support your answer.
(B) Does a linear trend appear to fit these data well? If so, estimate and interpret the linear-trend model for this time series
(C) Is there evidence of some seasonal pattern in these sales data? Explain how to forecast future values with the linear model.