Home advantage is a factor in sports. We all know that, even if the why isn’t always clear (there are lots of ideas). I’ve been doing a fair bit of academic research on the subject as it pertains to volleyball. That’s destined to get published before too long (I hope!). When it does, I’ll share the findings in a separate post (thus the Part 1 in the title of this one).
As a sort of aside to that other work, however, I did a quick bit of analysis looking at a potential aspect of home advantage causation. That’s referee bias.
There are two areas where we can point to potential bias. One is line and block touch calls. Whether the ball is in or out, or touched the block, is entirely objective. Any time borderline calls have to happen in a split second, though, bias can creep in. Unfortunately, I’m not aware of any data on that particular part of the game, making it hard to analyze. This leaves me to focus on the other area of potential bias. That’s ball-handling, which boils down to mainly double contacts on sets.
So I looked at the frequency of ball-handling errors (BHEs) called on the home team vs. the away team. In particular, I ran the numbers based on the 2019 NCAA Division I women’s season. It works out to a little over 4000 matches. Here’s what I found.
In the average match, the ref called the home team for a BHE on 0.62% of rallies. For visiting teams it was 0.70%. That difference is statistically highly significant, but we’re talking a difference of 0.12 points per match. So not something that’s determining the outcome.
Of course, this is a very basic analysis (comparison of means), and it’s a very narrow sample. Eventually, I’ll probably expand the study to multiple years and NCAA divisions, plus add in the men. There are also a number of potential influencing factors to examine (e.g. how refs call ball-handling can very from conference to conference).
If you’re interested in this kind of stuff, here’s some of the other volleyball statistical analysis I am working on.