The impact of the DP on MLS Playoffs

Get your team a DP if you want the best chance at this hardware.

In previous posts I have shown how the designated player (DP) in MLS is driving up league payrolls, and how team payroll has zero correlation to how you finish in the MLS regular season table. As I mentioned in the payroll/table post, there are many reasons for the lack of correlation. One of the more prominent ones is the roll of the playoffs, with the logical question being:

• If team payroll is being pushed by teams with DP's, do teams with DP's at least have a better chance at winning the MLS cup?

The Data

To determine if there is an effect from the DP, I must answer the two following questions:

1. Is there a statistically significant greater proportion of teams with a DP that qualify for the MLS Cup playoffs?
2. Once in the playoffs, do teams with a DP win more of the first round series?

Admittedly, the statistics that will be calculated here will be a bit limited as the DP has only been in place for three MLS seasons. This means there will be three proportions for two data sets for each of the two questions.

To create the data to answer the questions, I must create proportions based upon teams with and without DP's. Figure 1 shows such proportions for each season. Note that the denominators in each proportion change as teams were added to the league each of the years, and the number of teams taking advantage of the DP rule has increased over time. The two data sets test as normal, so two sample t-tests can be used to evaluate the statistics.

Figure 1: Proportion of teams in playoffs by team type

For the purposes of this analysis, teams with DP's were identified based upon those listed in the Wikipedia article on the topic. Compiled data can be found here.

Getting into the playoffs

When a two sample t-test is performed on this data, it becomes clear that teams with a DP have a distinct advantage in qualifying for the MLS Cup playoffs. See Figure 2 for the results of the test.

Figure 2: Results of two sample t-test of teams with and without DP

The p-value of 0.008 indicates that their is a low risk of incorrectly concluding that teams with DP's qualify in a statistically significantly greater proportion for the playoffs than teams without DP's. In fact, the estimated gap is 41%, with the lower 95% confidence of that gap being nearly 21%. The DP may not be causing this directly - perhaps having a DP is a sign of a club that has a higher overall commitment to quality soccer than those who don't. Nevertheless, having or not having a DP on a team is a good indicator of a club's chances for the postseason.

It should then come as no surprise then that the first team to qualify for the playoffs in their inaugural season in nearly a decade - Seattle Sounders FC - had a designated player on their team in 2009.

Making the conference finals

The statistics are even bleaker for non-DP teams once the playoffs start. From 2007-2009, 83% of the teams who have made it through to the second round of the playoffs have had a DP on them. The only team to win a first round series without a DP was Real Salt Lake in 2008 and 2009, with their run in 2009 leading to an MLS Cup trophy by upsetting the team with the ultimate DP - the LA Galaxy and David Beckham. Until that point, MLS Cups had been contested between two teams that each had a DP.

Conclusions

While spending on the DP and other players varies wildly from club to club, the impact of the DP cannot be underestimated. Whether it is an outsized impact on the pitch, or that they represent an increased level of commitment to the entire team by the ownership, having a DP on one's team goes a long way to predicting postseason qualification and performance. The Philadelphia Union do not have a DP, and thus will likely not repeat Seattle's performance in qualifying for the postseason in their expansion year. The Vancouver Whitecaps and Portland Timbers should heed the numbers, and look to spend a modest amount of money on a DP in their first season in MLS in 2011.

It will also be interesting to watch how the addition of a second and third DP to teams will impact the results of playoff qualification and first round outcomes. This will surely be a topic I revisit at the conclusion of each season.