Wednesday, March 13, 2013

What's Age Got to Do With It? Can 37-Year-Old Jimmie Johnson Beat the Odds?

Let's take a look at how driver performance changes throughout the course of their careers. Is there an age at which drivers are at their highest potential? Do they peak?

We will examine an aging curve to try to answer this question.

We've already seen a lot of work with aging curves in baseball, specifically by Bill James and others who followed him. We can apply this same concept in NASCAR.

Top Speed
First, let's focus on the statistics that represent the most extreme end of high performance: wins, poles, and laps led.

We see in Figure 1 that driver wins peak at age 30. Based on this plot, a typical driver shows consistent improvement through their 20s, peaks at 30, remains steady in their 30s, and then drifts slowly downward after 40.

The amazing thing about Figure 1 is how poles, wins, and laps led are so closely interrelated: They appear and disappear exactly at the same ages.

Also relevant is the slope from 20 to 30, relative to the slope from 30 to 50. Drivers show rapid improvement in their 20s, and a much more gradual decline as they grow older.

Just to be clear with more supporting evidence, you see the same age characteristic for Top 5s and Top 10s, here in Figure 2, again both peaking around age 30.

Driver Examples
Jimmie Johnson demonstrates performance consistent with our aging curve. He won his first title in his age 30 season, his highest win total came at age 31, and his most poles came at age 32. In the past two seasons (ages 35+36), he did not win titles, and averaged 3.5 wins and 2.0 poles. That's a decrease from his average of 7.0 wins and 3.4 poles per year in his five title seasons aged 30-34. Has Johnson peaked? It's hard to imagine how that could actually be possible given how much of a threat he still is every week, but the past two seasons statistically may foreshadow a downward trajectory in career performance as Johnson approaches his 40s.

On the contrary, Mark Martin, who defies all age-related statistics, peaked in wins (7) when he was 39, with his next two best seasons (5 wins each) coming at ages 34 and 50.

Matt Kenseth, who won this past weekend on his 41st birthday, peaked in wins (5) when he was 30, exactly as the aging curve suggests. Accordingly, is it too much to ask to expect a career resurgence from him?

Looking to the Future
Look to the young guns, who still in their 20s, should keep getting better: Ricky Stenhouse, Aric Almirola, Joey Logano, Brian Vickers. We haven't seen a lot from them in the past, but there is so much upside to their careers still. Even true stars like Kyle Busch and Brad Keselowski, as excellent as they have been already, still have near-term upside in the next couple years.

Hope is Not Lost for the Veterans
The conventional wisdom about veteran drivers is they know how to get things done, save their equipment, and get to the end of the race. They are smarter about how to handle situations because they can use their mind and experience, not just pure speed. Well, the good thing about all that wisdom is seeing the numbers match up:

Figure 3 shows that a driver's ability to be running at the finish increases all the way until about the age of 40, and only barely drops off until the age of 45. This is a very different profile than the winning curve. Older drivers are actually better about getting their equipment to the end of the race.

Figure 4 says the same thing, that drivers in their 40s are doing a good job of getting Lead Lap Finishes. They know how to stay in the race until the end, and be around for a decent finish. Again, the peak for Lead Lap Finishes is near age 40, with decent performance into the mid 40s. These older drivers may not be able to win as much, but they still find ways to drive smartly, avoid crashes, and make it to the end of the race.

The Summary
If you are looking for extreme high-performance, look for drivers aged around 30. The potential upside comes from the young guns in their 20s. Drivers who have hit 40 should not be expected to do better than their past glory days. But they can still drive well enough to get their car to the finish line.