Measuring Referee Bias in BPL

Ask any fan their opinion of BPL referees and the responses will range from "mediocre" on the positive side of the spectrum to "#$%&..." on the more negative side.  These fans make their feelings known every match day, often vociferously.  It is possible that certain referees may hold biases against certain clubs, players or managers, but- in particular- the home/away bias has been noted in a multitude of prior studies.

Perhaps the most subjective decisions, and therefore most susceptible to bias, a referee makes is determining when a card should be shown to an offending player.  These decisions can often appear maddeningly inconsistent.  Indeed, we looked at the number of fouls committed per card for each BPL team (home and away) and found a pretty significant difference.  On average it takes a home team 6.6 fouls before they receive a card while for away sides it only takes 5.6 fouls.  Perhaps, just as a player might be said to "see red" in a fit of madness, a "yellow mist" might besiege a referee in front of thousands of baying fans.

See below for a team by team breakdown.  Chelsea is subject to the largest disparity in home/away fouls per card.