In an interesting twist, fast-food giant McDonald's (NYSE:MCD) has evolved into one of the fast-food industry's hot stocks while former Wall Street darling, Chipotle (NYSE:CMG), has seen its stock dive lower over the past few years. During the past three years, McDonald's stock is up 90% and Chipotle stock is down 53%.

Their divergent stock prices are the result of the continued strength and consistency of McDonald's comparable sales growth and the company's execution on its strategic transformation plans. Meanwhile, Chipotle has suffered from public relations missteps and unimpressive comparable sales growth.

But can McDonald's stay in the spotlight in 2018? Its first test for the year will come when the fast-food giant reports fourth-quarter results later this month. Management is scheduled to share an update on the quarter on Jan. 30. Ahead of the results, here's an overview of some the key areas investors should watch.

A group of young people eating fast food

Image source: Getty Images.

Systemwide sales growth

Since McDonanld's reported total revenue each quarter is meaningfully impacted by its ongoing strategic-refranchising initiative, growth in systemwide sales is arguably a better representation of the company's total operational growth than revenue growth.

In McDonald's most recently reported quarter, or its third quarter of 2017, systemwide sales increased 7% year over year in constant currencies. Management said the metric was driven by strong growth in comparable sales and restaurant expansion.

For Q4, look for McDonald's to deliver systemwide sales growth close to the 7% increase it reported in Q3.

Comparable sales growth

Probably the most watched metric in McDonald's quarterly reports its comparable sales (also called same-store sales) growth, or sales growth at stores open more than a year. McDonald's has been on quite a streak with its comparable store sales growth, reporting positive growth for nine quarters in a row.

In McDonald's third quarter, same-store sales increased 6% year over year, slightingly below the 6.6% growth in the metric in Q2, but still strong. McDonald's said the strong growth in comparable sales was driven by positive growth in guest counts across all geographic segments.

Showing why investors love McDonald's growth in same-store sales so much, consider how much higher the metric is than Chipotle's recent same-store sales growth. In its third quarter, same-store sales increased just 1%. Wendy's same-store sales during the same period were up 2% year over year. 

Digital efforts

Last, investors should look for an update on McDonald's important digital efforts.

A woman using a smartphone

Image source: Getty Images.

In a new growth plan revealed last March, McDonald's committed to enhancing its digital capabilities and technology "to dramatically elevate the customer experience."

Early efforts in this area have been promising, but McDonald's is just getting started.

Several areas to watch regarding McDonald's digital efforts are its monthly active digital users, total app downloads, and the number of restaurants it has rolled out mobile order to during 2017. As of its most recent quarter, McDonald's had 9 million monthly active users for its digital products and its app had 30 million downloads. Further, management was planning to roll out mobile ordering to 20,000 restaurants by the end of the year.

Look for significant growth in active users and mobile app downloads, as well as the achievement of its 20,000-restaurant target for mobile ordering.

Daniel Sparks has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Chipotle Mexican Grill. The Motley Fool has a disclosure policy.