[we'd like to thank Prof. Paul Jakus, @paulj, for yet another thought-provoking statistical analysis of Phish.net data - ed.]

Phish.net show ratings are meant to convey Phish fans’ collective perception of how good a show was, but these ratings are subject to a number of biases. For example, .net ratings do not come from a random sample (sampling bias), and people tend to rate the shows they’ve attended quite highly (attendance bias).

Another possible bias, which the .net Cognoscenti have termed “Recency Bias”, is the tendency to rate a show during the first few days after the performance, if not immediately after the show. It is believed that ratings posted in the immediate aftermath of a concert will reflect the warm glow of that experience. People have not taken the time to reflect on the quality of that show relative to the performances immediately before or after, or within the context of an entire Phish tour. Recency bias implies that a show’s rating will decline as its warm glow dissipates.

It occurred to me that I could estimate the magnitude of recency bias using a Phish show database I’ve periodically updated since Summer 2018. We’ll look solely at the 21-show Summer 2018 tour, which started at Lake Tahoe on July 17 and ended at Dick’s on September 2. For each show, we can use snapshots of .net ratings taken on October 2, 2018, on May 5, 2019, and on April 2, 2020. Thus, we have ratings taken one month after the conclusion of tour, 8 months after tour, and 19 months after tour.

Here are the ratings time paths of three Summer 2018 shows [Gorge Night 3 (7/22/18), Bill Graham Civic Auditorium Night 2 (7/25/18), and The Forum Night 1 (7/27)]:

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