We consider the algorithmic challenges behind a novel interface that simplifies consumer research of online reviews by surfacing relevant comparable review bundles: reviews for two or more of the items being researched, all generated in similar enough circumstances to provide for easy comparison. This can be reviews by the same reviewer, or by the same demographic category of reviewer, or reviews focusing on the same aspect of the items. But such an interface will work only if the review ecosystem often has comparable review bundles for common research tasks.
Here, we develop and evaluate practical algorithms for suggesting additional review targets to reviewers to maximize comparable pair coverage, the fraction of co-researched pairs of items that have both been reviewed by the same reviewer (or more generally are comparable in one of several ways). We show the exact problem and many subcases to be intractable, and give a greedy online, linear-time 2-approximation for a very general setting, and an offline 1.583-approximation for a narrower setting. We evaluate the algorithms on the Google+ Local reviews dataset, yielding more than 10x gain in pair coverage from six months of simulated replacement of existing reviews by suggested reviews. Even allowing for 90% of reviewers ignoring the suggestions, the pair coverage grows more than 2x in the simulation. To explore other parts of the parameter space, we also evaluate the algorithms on synthetic models.