Too Much Football: Is There A Connection Between Matches Played and Goals Per Game?

Over the past couple of weeks, I've been writing about league characteristics, including average goals per match and league balance. As we've been digging a little more into the data, Benjamin Leinwand and I have noticed a slightly curious pattern: goals per match seem to be correlated with the number of matches played in a season. We've all heard the common complaint that England's players aren't doing as well in international competitions as their performance in league play would suggest, with fatigue after a long season often cited as one of the factors. Could there be something to this?

So here's what we did: we took the goals data we collected for the six leagues we've been talking about (Bundesliga, EPL, Eredivisie, La Liga, Ligue 1, and Serie A) for the 1995-2010 period and calculated the average number of goals per match for seasons and leagues that saw 34 league matches and compared them to those that involved 38 league matches.

And lo and behold, averaged across the leagues and years, we see that there is a distinct difference between the two season/league formats: leagues where teams play 38 matches see 2.54 goals while leagues with 34 matches see 2.82. And that difference is highly significant, statistically speaking. So could this be behind some of the scoring differences we see across leagues?

To check on the consistency of this pattern, we went one step further. Turns out, during this time, four of the six leagues went through changes in league formats. The English Premiership and La Liga each had two seasons of 42 instead of 38 matches; Serie A had six seasons of 38 instead of 34 matches; and Ligue 1 had five seasons of 34 instead of 38 matches. In contrast, the Bundesliga and Eredivisie consistently played 34 matches the entire time. We would expect to see fewer goals in those seasons when leagues went to a format with more teams and matches.

One caveat: given the relatively small number of seasons involved, it's best not to make too much of any differences, but it's interesting to see nonetheless. So here are goals per match for each league separately, by the number of matches played in the season.

Overall, we do see that goal totals decrease with more matches played in three of the four leagues that experienced seasons of varying length. Goal averages are higher when fewer matches are played in Serie A, the EPL, and Ligue 1, while goal totals were up in La Liga during their 42 match seasons.

But I'm still skeptical, and here's why: the two leagues that have consistently played 34 matches also happen to be the highest-scoring 34 match leagues (the others are Serie A and Ligue 1 during this period), and there may be reasons having nothing to do with season length that drive these outcomes. So there's a good chance the pattern in the first graph is more marked because of their inclusion. And of course, we are not accounting for league quality and the extent to which some teams' seasons are actually much longer than 34 or 38 matches because of European competitions. Still, we thought the pattern was well worth thinking about ...