If you’ve watched the Premier League for a few seasons you’ve probably noticed that certain teams finish at the top each year. Man City, Man United, Arsenal and all the heavy spending teams usually have a spot in the top five by the time the whistle blows on the 38th game of the season. The same thing is happening this year with City, Arsenal, Liverpool, and Chelsea occupying the top four spots in the table with ten games completed.

This got me thinking about consistency in the Premier League. Are there some teams that finish in about the same position each year, and some that have sporadic performances year to year? To answer this question I looked at the finishing position of current teams that have been in the Premier League at least five of the last ten seasons.

The first thing I looked at was a visualization of each team’s finishing positions in the League the past ten seasons. Here’s a set of box plots for every team that met the above requirements, ordered by current position in the standings.

Looking at these first four plots, it appears Arsenal is by far the most consistent team of the bunch. Chelsea is also looking rather good, but they have two outlier finishes represented by the hollow dots. City’s finishes are all over the place. If you’re not sure how to read a box plot, check out this quick article here.

The next grouping looks to be fairly even across the board. Stoke are particularly interesting as their finishes are fairly consistent but they are all outside of the top five. This could mean that quality of a team doesn’t effect their consistency. For example, a middle of table team could be just as consistent as a top of table team. We’ll come back to this in a bit.

The final group is led by Swansea, who are consistently between the 9 and 12 marks. West Ham is all over the place year to year with a huge middle 50% spread.

Looking at the plots is a good way to visually represent the data, but it’s hard to tell exactly how consistent a team is from the plot. So to answer our question of consistency, I calculated the standard deviation of each team’s finishes as well as their mean finish. Standard deviation is a measure of the amount of variation of data values around the mean. A lower standard deviation means that a team has been more consistent.

The table reaffirms what we thought earlier about Arsenal: that they are the most consistent team. Their standard deviation is almost a full point under the second most consistent team, Swansea. Arsenal’s SD means that on average their finishes are 0.7 places from their mean finish, 3.4. On the other end of the table is Man City (!) with a SD of 4.2. I didn’t expect that at all when I started looking at this question. City have been the most inconsistent team over the past 10 years, missing their mean finishing place by 4.2 places on average each year.

I said I’d be revisiting the idea that the better teams are more consistent too, and now I’m doing that. We can kind of get a gauge of how the better teams fair in terms of consistency by looking at the table, but plotting the data is a much better method of doing this. Here’s a plot of average finishing position against SD of finishing position.

If the better teams were more consistent, we would see a strong positive correlation on this graph. So when SD goes up, average finishing position goes up (re: closer to 20) too. But that’s not what we see. The points seem to be scattered all over the place with no definitive pattern, and the correlation confirms this — the r value of this data is just 0.28.

It’s fairly safe to say from this analysis that the better teams aren’t more consistent than the worse ones. It varies on a team by team basis and trying to predict average finishing position based on a team’s SD of finishing position wouldn’t prove to be very accurate. The limitation to this claim is that nowhere in our data set is there a team that had a mean finish of 15th place or lower. That could be just out of bad luck (we only looked at teams currently in the Premier League) or it could mean that the really poor teams — the ones that finish lower than 15th in the table — aren’t consistent enough to remain in the Premier League year after year.

I would say it’s more likely that we were just unlucky, though. Of the teams that weren’t in the Premier League all ten of the last seasons that we looked at (Stoke, West Brom, Swansea, and Sunderland), none of them had an extremely high SD. West Brom was the outlier of the group with a SD of 3.8, but all of the others had a SD below 2.2. If the teams that got promoted from the Championship and relegated from the Prem were more inconsistent, we would expect to see the SD of these teams to be a lot higher. An alternate explanation is that the four teams we just looked at are more consistent than the “average” promoted Championship team and the bulk of promoted teams would be more inconsistent. We can’t say definitively if either of these explanations are the case or not, but we can say that there’s very little relationship between a quality of a team and the consistency of a team for the top 15 spots and perhaps for the last five spots as well.

This analysis helped to answer the question of consistency in the Premier League while also bringing up more questions to explore in the future. To recap, the key takeaways from this analysis are:

Some teams are definitely more consistent than others

Arsenal are easily the most consistent team year over year

Man City are the least consistent

The quality of a team doesn’t effect their consistency for at least teams with an average finish of 1-15

And some questions that I’d like to look at after doing this analysis:

Are teams that have an average finish in the 15-20 range more inconsistent than the rest of the teams?

Are there certain qualities that the most consistent teams all possess (high passing accuracy or a good shots-on-target ratio, for example)?