Tuesday, September 04, 2007

Track and field: wind-adjusted 100-metre records

Here’s an article by K. Duffy on how wind affects times in the 100-metre sprint.

According to the article, the IAAF won’t recognize a world record in this event if it was run with a tailwind of more than 2 meters per second (which is a gentle wind indeed, at less than 4.5 mph). Is that an overreaction? Just how much does the wind assist a runner in this event?

Duffy refers us to a couple of studies by J. R. Mureika (unfortunately, the links to those studies are no longer valid). He then uses Mureika’s method to correct every annual top-20 performance from 1998 to 2002.

From the charts provided, it seems like every 1 m/s of wind speed is worth about .05 seconds. Maurice Greene’s 1999 world record, 9.79 seconds, was run with the assistance of an 0.1 m/s wind. That means his “adjusted” time is about 9.80 seconds (probably slightly less, but apparently high enough to round to 9.80). That’s still good enough for the best adjusted time ever.

Going by the data provided, it seems the method does indeed have something going for it. Duffy lists every 100-metre race that clocked under 10.00 seconds, and does all the adjustments. And it turns out that the best times did in fact occur in favorable wind conditions.

If wind had nothing to do with speed, you’d expect the best “adjusted” times to be better than the unadjusted times. That’s because if the adjustment is random, then, just by luck, you’d have expect at least some of the best times to have adjustments that make them even better. But adjusting all the times actually makes the best performances look worse – and, in fact, it reduces the number of “extremely good” times.

With the adjustments, there were only 19 times at 9.89 or better. However, if you look only at the raw, official times, there were 32 such races. This difference would be quite unlikely if the wind adjustment wasn’t measuring something real. (Caveat: since Duffy lists only the top-20 times for each year, it’s possible that there’s some selection bias affecting the “adjusted”count – a mediocre time run into a strong headwind might not have been good enough on a “raw” basis to make the list. But that’s fairly unlikely, since the list goes pretty far down, and contains no winds strong enough to cause that large an effect.)

Still on that list of the best 100 races, Duffy reports that 75% of them were run with a tailwind. Again, that strongly suggests the wind is a major factor.

Up until 2002, there were three instances of races won in less than 9.80 seconds: Ben Johnson (9.79 in 1988), Maurice Greene (9.79 in 1999), and Tim Montgomery (9.78 in 2002). All those adjust to worse figures (9.85, 9.80, and 9.89 respectively) when you consider wind. Since 2002, there have been
four times of 9.77. All of those were run with tailwinds of at least 1.0 m/s, which would result in an adjustment to at least 9.82 seconds.

So it looks like the 9.80 mark is yet to be broken, on a wind-adjusted basis.

(Thanks to Alan Reifman for the link.)



At Thursday, September 06, 2007 2:53:00 AM, Anonymous Anonymous said...

Working links to download the Mureika articles cited by Duffy are 9.84 vs 9.84: A Matter of Time and The Legality of Wind and Altitude Assisted Performances in the Sprints"
The adjustments used are both wind and altitude adjusted. Altitude adjustments can be a significant portion of the overall adjustment. There are selection biases. Very fast times with illegal tailwinds are omitted from Duffy's adjusted list (notably Obadele Thompson's 9.69 at 1200 m altitude with a 5.7 m/s tailwind), and insufficiently fast raw times produced into strong headwinds are also left off Duffy's list [Duffy notes 3 or 4 exceptions just over 10.00 which he personally added to his charts, but others could be found ]. Mureika has a calculator which includes at least some of these performances in more extreme conditions.

At Thursday, September 06, 2007 8:33:00 AM, Blogger Phil Birnbaum said...

Thanks, Joe!

At Thursday, September 06, 2007 8:34:00 AM, Blogger Phil Birnbaum said...

First link didn't work for me.

At Thursday, September 06, 2007 10:36:00 AM, Anonymous Anonymous said...

Sorry, try this for the first link. Playing around with the tool Mureika provides (backed by a database through 2006) shows that when the top 500 adjusted times (by his method) are considered, something like 263 were performed with a tailwind and 192 with a headwind [45 with no wind]. When raw unadjusted times are considered, around 80% of the top 500 had a tailwind.

There are some factors involved here which will not even out. The benefits of a tailwind are obvious and have been known for a long time. Consequently, when feasible, tracks are oriented (and meets are scheduled at times of day) when favorable legal winds are more likely. Everyone (athletes, fans and thus meet organizers and sponsors) have an interest in fast legal times. In general the highly competitive meets which produce these top times should have more favorable conditions than would occur randomly. There are difficulties with the data collection as well. Historical lists focus on the legal times, so fast but illegal times will be under-represented. I checked several years' worth of annual lists on the IAAF website, and they do not systematically record illegal wind-aided times before 2003. Fast illegal times before that may be underrepresented ...

As Duffy and Mureika note, electronic timing is far more accurate and precise than the environmental data used to make the adjustments. The average adjustment by Mureika is on the order of a tenth of a second, or 1%.

At Sunday, September 09, 2007 10:20:00 AM, Blogger Jon said...

Hi, Phil! It was nice to see you in Saint Louis.

Maybe Andy Beyer should come up with speed figures for human runners as well as horses.

At Sunday, September 09, 2007 11:08:00 AM, Blogger Phil Birnbaum said...

Hey, Jon,

Ha! I have to admit, I'm surprised by how much more consistent the humans look after you correct for speed. Someone should calculate the odds of runner X beating runner Y if he's (for instance) usually .05 seconds faster on average. I bet the probability would be pretty high.

At Sunday, September 09, 2007 3:24:00 PM, Blogger alan said...

Asafa Powell just lowered his world record to 9.74.


I'll be interested to see what the wind/altitude adjusted time turns out to be. It would seem likely that, even if some hundredths of a second get added on, his adjusted time would still be below the adjusted record of 9.80.

At Sunday, September 09, 2007 5:11:00 PM, Anonymous Anonymous said...

Using Mureika's calculator, Powell's 9.74 world record today in a semifinal at Rieti, Italy [400 meters altitude] with a 1.7 m/s tailwind adjusts to 9.83 in neutral conditions. However his 9.78 in the final with zero wind converts to 9.79, now the fastest adjusted time ever. Incidentally, Tyson Gay who won the world championship 2 weeks ago, has twice run "adjusted" times of 9.82 this year. Powell and Gay are expected to race head-to-head again next week in Belgium.

At Monday, September 10, 2007 11:26:00 AM, Blogger Phil Birnbaum said...

My local paper didn't mention the idea of adjusted times at all, just that the 9.74 will count since the wind speed was low enough to make it legal.

At Monday, September 10, 2007 11:17:00 PM, Blogger alan said...

Wind/altitude adjusted times tend to attract interest only in sabermetric circles. The only thing that seems to get mainstream sportswriters thinking along these lines is when world records get broken at extreme altitude, such as all the records that fell at the 1968 Mexico City Olympics.


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