Groupon Inc.’s mobile app is an anomaly in today’s app economy.

The retailer rarely make mistakes when it releases a new version of its mobile app, says Ben Gray, digital experience analyst at the Application Resource Center, the research arm of app quality and testing company Applause App Quality Inc.

And shoppers notice. Groupon, No. 26 in the Internet Retailer 2016 Top 500 Guide, has immensely positive app store ratings and reviews, which is why the retailer of daily deals and physical goods has clinched the top retail app spot in ARC’s annual retail app report, “How Customers Rate the Mobile Retail App Leaders,” released today.

ARC reviewed the Android and iOS app quality of the top 43 retailers that derive more than 40% of their 2015 mobile sales from apps, according to Internet Retailer’s 2016 Mobile 500.

The research firm analyzed the app store ratings and consumer reviews for those apps in both the Apple App Store and Google Play. Apps were required to have more than 150 reviews to qualify for the study.

In addition to the reviews, ARC weighed several other app metrics, including usability, encouragement of repeat purchases, and performance under heavy or unexpected demand, such as during sales, says Gray, the author of the report. The firm then applied a rating between 0 and 100 for both the retail company’s Android app and iOS app. The app’s final score was an average of the two scores.

The 43 apps in the survey averaged a score of 52 out of 100, which is lower than ARC’s average of 67.3 across all verticals including, travel apps, restaurant apps, dating apps and healthcare apps.

While retail apps as a whole may leave consumers wanting, Groupon shoppers are pleased, Gray says. Out of 151,562 Android reviews and 220,473 iOS reviews, Groupon’s app achieved a score of 83.0.

“Groupon’s iOS mobile sentiment level hasn’t dipped below 80 since March 2011 and its Android score has never seen below 80 in its four years of existence,” Gray says.

The retailer’s teams collaborate to respond quickly to in-app feedback, which is why it has such a high user sentiment score, Gray says.

No. 2 on the list is home furnishings retailer One Kings Lane, No. 104 in the Top 500, with an app score of 82.0. The retailer blends content with commerce well, Gray says.

“The app reminders alert customers to new sales,” he says. “Its alerts drives a sense of urgency, its high-quality images engender confidence that the product is the perfect home companion and it embraces social to spread the wealth among friends.”

Other apps that ranked high on the list include ModCloth Inc. (No. 187) at 79.7;, REI (No. 74) at 79.9; Rue La La (No. 80) at 77.6; Gilt Groupe (No. 69) at 75.9; and JackThreads (No. 209) at 75.8.

Several retailers had large swings in sentiment scores comparing this year to last year, including Staples Inc. (No. 5) and Peapod LLC (No. 65).

Staples moved up 9.3 points this year to achieve a score of 35.4. Staples made extensive investments in its app, including in-store maps, order tracking, an expedited ordering Visa Checkout button and barcode scanning.

Peapod scored 40.5, a decline of 11.5 points from the previous year. Shoppers continually give its iOS and Android apps one- and two-star reviews, citing freezes, slow performance, blank screens, error messages, disruptive ads and limited payment support options.

Toys R Us. Inc. (No. 35) ranked near the bottom  of the list with a score of 13.4. The toy retailer can likely improve its score if it updates its app more frequently, Gray says.

“It last released an Android update in January 2015,” he says. “And before its minor May 2016 update, its previous iOS release was in February 2015. That’s a long time in the digital world.”