Edit - Due to numerous requests for the addition of NHL data, I have added a second figure showing the distribution for hockey teams. These data come from http://www.sportingcharts.com/nhl/stats/, where overtime losses were counted as a half win. A normal length NHL season has 82 games.

All-stars and franchise players are a crucial aspect to winning consistency for sports teams. Lack of these players can mean a rough season. But how quickly do these winning (and losing) streaks change?  If your team is at the top of the league, can you expect another good season next year?

This series of graphs shows the percentage of games won during consecutive seasons for three sports: Baseball (MLB), Basketball (NBA), and Football (NFL). Each data point represents the regular season winning percentage of a team during two consecutive years, with the earlier year on the x-axis. The data include the past 14 complete seasons of each team (fewer for expansion teams). The largest magnitude changes in winning percentage in each direction are labeled.

The violin plot echoes the spread of the data in the scatter plots. Baseball has the least change in season-to-season winning percentage; teams that are good tend to remain good and vice versa. Football has the most change from season to season; a mediocre team can make a sudden comeback in just a year.

There are several possible reasons for this result. One is the length of the season. Baseball has by far the longest season (162 games per team). Basketball has 82 games and football, 16 games. The more games, the less impact that a set of fluky wins or losses will have on a team’s overall winning percentage. Another possible factor is the equality of teams in terms of skill. Baseball teams rarely win more than 60% of their games, but this is common in basketball and football, suggesting that baseball teams may be more evenly matched.

So if you are a baseball fan and your team is terrible, you’re likely in for a rough stretch. I suggest switching to football, where your bottom-of-the-barrel team can make a quick turnaround, only to lose in the Super Bowl. Go 49ers!

Data source: http://www.sports-reference.com/

Posted on 5 November, 2013

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    interesting sports data.
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