Tiffany was founded in 1837, when Charles Lewis Tiffany opened his first store in downtown Manhattan. Tiffany retails and distributes a selection of Tiffany & Co. brand jewelry at a range of prices. Today, more than 150 Tiffany & Co. stores sell to customers in U.S. and international markets. In addition to jewelry, it sells Tiffany & Co. brand merchandise in the following categories: timepieces and clocks; sterling silver merchandise; stainless steel f latware; crystal, glassware, china, and other tableware; custom engraved stationery; writing instruments; and fashion accessories. Fragrance products are sold under the trademarks Tiffany, Pure Tiffany, and Tiffany for Men. Tiffany also sells other brands of timepieces and tableware in its U.S. stores.

Tiffany?s quarterly sales from 2005 to the middle of 2017 are in the file Tiffany 2017. They are shown here.

Build alternative time series models for Tiffany?s sales and forecast future sales. In addition, find supportive economic data, such as gross domestic product (GDP), consumer price index (CPI), disposable income, unemployment, and interest rates over this same time period, and try using them in a regression model. For any model be sure to plot residuals over time and interpret what you see. Comment on any trends in the recent growth of Tiffany?s sales. Compare your models and recommend a model for the executives at Tiffany to use for forecasting their quarterly sales.

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1200000 1000000 800000 600000 2005.0 2007.5 2010.0 2012.5 2015.0 Year Net. Sales