Tuesday, May 14, 2013

Kyle Busch and Kasey Kahne are NASCAR's Most Volatile Drivers

(This is a cross-post with StatsInsights)

A driver's average finish is often discussed in the media as a benchmark for how well that driver performs. However, this statistic only gives part of the picture; to really get a complete sense of a driver's performance, we also need to consider the volatility of those finishes.

What do we mean by volatility? Let's start with an example.

If driver A finishes 10th and 10th in two races, that's an average finish of 10.  But if driver B finishes 1st and 19th in two races, that's also an average of finish of 10. However, driver B shows a lot more volatility in getting to the same average.

Drivers with higher volatility are more likely to have extreme finishes. Lower volatility means the drivers consistently finish around the same spot. The statistical parameter that we'll use to help us make this assessment is the standard deviation of a driver's race results.

Looking at the Data

Figure 1 shows all the drivers who have run at least 100 races since 2005 (when Loop Data statistics became available) and who have had an overall average finish better than 22 (to discard teams with consistently bad results, start-and-park teams, etc).

We see here that Kyle Busch, Kasey Kahne, and Kurt Busch are the three most volatile drivers. They have a history of extreme finishes, which means that they are more likely than other drivers to either finish way up front or way in the back.

Notice that championship drivers are generally in the upper half of the volatility scale. Jimmie Johnson, Kurt Busch, Jeff Gordon, Tony Stewart, and Brad Keselowski all show above-average volatility compared to other drivers. This suggests that volatility is a good thing, not a bad thing: In order to win championships, you need some volatility (but not too much).

Figure 2 shows the most volatile individual driver seasons since 2005:

What observations can we make?

Notice we see many of the top drivers on this list.  In fact, drivers like Matt Kenseth, who don't normally seem to have extreme finishes, still appear on this list.

Also notice in Figure 2 we see Mark Martin's 2009 season. This season is interesting because he was 34th in points after 4 races, but got all the way to second in the final points standings. That's because of high volatility: engine failures and crashes early in the year, followed by a string of wins later in the year.

Jimmie Johnson has three seasons on this list, but in two of them, he didn't win the title. And in 2010, he had to come from behind in the final race of the year to win the cup. Other than Johnson in 2010, there are no championship seasons shown in Figure 2.

This data helps reinforce the idea that there's an "ideal" level of volatility, an above-average amount that can help a driver have a great season.


How can people use this info? If you are a fantasy league player or team owner, it's important to look beyond just the average finish when you pick which drivers you think are going to do well. Look at their volatility too, because that suggests the ability to get race wins (but also an increased tendency to crash out of races). High volatility drivers give you more risk and more upside. Low volatility drivers are consistent, but the numbers suggest they probably won't win you many races.

Look at the example below in Figure 3. You see that Kyle Busch has about the same average finish as Mark Martin, Greg Biffle, and Clint Bowyer (similar sized magenta bars). But if you were betting on who would win a race, you'd want to go with Busch because he has a much higher volatility.

The key is adding this second datapoint for every driver to get a better picture for how they are driving. A driver needs to have some volatility to have a great season. Not too much, but just the right amount.