Jakob Kiplimo’s sensational world record half marathon (56:42) in the eDreams Barcelona Half Marathon immediately recalled last year’s most incredible road performance–the 2:09:56 marathon that Ruth Chepngetich ran in Chicago. It also marks the starting line for discussions of his possible sub-two-hour marathon in London this April.
Kiplimo, a 24-year-old Ugandan running prodigy, erased the previous half-marathon record of 57:30 set by Ethiopian Yomif Kejelcha last October in the Valencia Half Marathon. Prior to Kejelcha, Kiplimo had himself held the record. In November, 2021, he ran a then-world-record 57:31 in Lisbon.
The eDreams Barcelona Half Marathon course follows a figure-8 design with the start and finish very close to each other. Overall, the course rises 25 feet from start to finish. This should make it a fully legal road course according to World Athletics regulations.
While Kiplimo broke Kejelcha’s record by a whopping 48 seconds (and his own best by 49 seconds), those numbers pale compared to what Chepngetich achieved last October in Chicago. There, the 30-year-old Kenyan star beat the previous world record (Tigist Assefa, 2:11:53, Berlin 2023) by almost 2 minutes (117 seconds) and her own personal best (2:14:18) by 4 minutes and 22 seconds.
When we put Kiplimo and Chepngetich side by side, it’s natural to ask two simple questions: Which performance was superior? Which performance was more surprising?
That’s what I’ll do in the following paragraphs and tables.
In the first case, we turn to World Athletics newly updated (last month) scoring tables. These tables–700 pages long–attempt to compare performances in any event with performances in every other event. They give every performance, whether by a male or female athlete, a single “score.” The maximum allowable score is 1400.
On these tables, Kiplimo scores 1323 points and Chepngetich 1312.
Now, let’s look at the second question. Which performance was more predictable, and therefore less surprising? This analysis isn’t usually applied to endurance performances, but there is a powerful logic to it. The more predictable and less surprising a runner’s time, the more we tend to believe that the runner’s performance was unassisted by course differentials, pacers, wind and other weather factors, and of course doping.
To answer this predictability/surprise question, I looked at Kiplimo’s and Chepngetich’s two best performances in each of the three years prior to their eye-popping world record. I gave them credit for their best races, and didn’t penalize them for their less impressive days.
This isn’t a perfect system–none are–but it’s simple and mathematical. I averaged their two best performances for each of the three years, and then averaged the averages. (I used the World Athletics scoring table.)
This gave each of them an average score prior to their recent world record. I then divided the score for the new world record by the average score of the three recent years. This gives us a “surprise” rating. The bigger this number, the more surprising the world record performance, because it substantially exceeded performances that had come before.
By definition, every world record will have a “surprise score,” as I’m now calling it, that is greater than 1.0. Otherwise it wouldn’t be a new world record. Beyond 1.0, the higher the score, the less expected (more surprising) the outcome.
Here, Kiplimo has a score of 1.056 for his half marathon record, and Chepngetich a score of 1.058 for her marathon record. So Chepngetich’s race was more surprising and less predictable when compared to her prior performances.
As a footnote, I’ll also note that Kiplimo did some fast road racing toward the end of last year that was not included in this analysis. At the same time, Chepngetich’s relatively weak running in 2024 (before the Chicago Marathon) was not used to penalize her.
Nice analysis Amby. A simpler perusal of each of their performances over the past few years suggests that Chepngetich’s marathon was considerably more surprising than Kiplimo’s Barcelona Half – which was also beyond surprising. May future improbable performances not subsequently be called Chepngetichesque? 🙂