Calculating Rank Ordering Error Metric for implicit recommendation
I found a video called "Evaluating Implicit Ratings Models" by Datacamp. It is an explanation of evaluation of recommendation engines that use Implicit Ratings. Although they refer to the metric differently by calling it Rank Ordering Error Metric, the formula they give is identical to the one defined in the paper I linked in my question. Following along with the examples in the video and plugging in the values from their examples, I get the same result they do. I guess it seems slightly less than intuitive but I appear to be understanding how it works correctly anyway.