Something Every Football Fan Knows to Be True May Be False

All of this season's Champions League quarter-finals were won by the teams that played the second leg at home. Most fans won't be surprised: We all know that playing the second leg at home is a huge advantage, right?

I looked at data on all previous CL seasons' two-legged knockout fixtures but excluded all first knockout stage fixtures, because in these cases, whether you play the second leg at home is determined by previous performance in the tournament. (In scientific parlance, assignment to conditions is nonrandom.)

It turns out that exactly half of the fixtures were won by the teams that played at home first, which suggests that one of football's most cherished wisdoms is wrong. Two caveats, however: 1. Obviously, if you'd add the results from this season's quarter-finals, this would alter the outcome - but let's see how the semis go first. 2. The sample is pretty small (n=42). I'd like to collect someone else to collect a much larger data set and repeat the analysis. If you're aware of any such analysis, please let me know.

Earlier: What's a good first-leg result?