We weigh the severity of each type of problem to create a predicted reliability score for each vehicle, from 1 to 100. We use that information to give reliability ratings for every major mainstream vehicle. (The reliability rating is then combined with data collected from our track testing, as well as our owner satisfaction survey results and safety data, to calculate each test vehicle’s Overall Score.)

https://www.consumerreports.org/cars/car-reliability-owner-satisfaction/who-makes-the-most-reliable-cars-a7824554938/

The issues are weighed by severity. So being left stranded weighs more heavily than a leaky sunroof.