Over the past few years, smartphones have almost entirely occupied the mobile phone market. As a result, smartphone manufacturers have to face fierce competition to enter the market and increase, or even maintain, market share. The file Smartphone contains the global market share (in percent) held by two smartphonemanufacturer, Huawei and OPPO, between the first quarter of 2015 and the second quarter of 2018.

For each of the two time series,

a. plot the data.

b. compute the linear trend forecasting equation and plot the trend line.

c. compute the quadratic trend forecasting equation and plot the results.

d. compute the exponential trend forecasting equation and plot the results.

e. determine the best-fitting autoregressive model, using \(\alpha=0.05\).

f. Perform a residual analysis for each of the models in (b) through (e).

g. Compute the standard error of the estimate \(\left(S_{Y X}\right)\) and the \(M A D\) for each corresponding model in (f).

h. On the basis of your results in (f) and (g), along with a consideration of the principle of parsimony, which model would you select for purposes of forecasting? Discuss. i. Using the selected model in (h), forecast the market shares for the third quarter of 2018.