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Duffy refers us to a couple of studies by J. R. Mureika (unfortunately, the links to those studies are no longer valid).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.)