# Fuelled by Data: How to Pace the London Marathon ???? ????????

Basically I want to know how much did a given runner slow down between the 5km mark and the 40km mark.

The formula below gives this number as a percentage.

‘Slowdown factor’ for a runnerAnyway, even if you ignore this formula then just know that the slowdown factor is a number that represents how much a runner’s pace slowed between the beginning and the end of the race.

Pretty chart: how much did different runners slow down?The above chart shows how much runners slowed down over the years.

I’ve split the results into different finishing times (runners who finished in under 3 hours, under 4 hours etc) and then by which year they ran the race.

You can see that fast runners didn’t slow down that much (maybe around 10%) which makes a lot of sense.

These runners are often experienced and know how to pace themselves.

The slower runners experienced a much larger drop in pace however.

Also interesting that 2018 was the worst year for slowing down, no matter the speed of the runner.

Let’s look at the weatherSo when runners complain about the weather, they normally mean its either cold (below 5C), hot (above 18C) or humid.

Running in the rain sucks too, but that’s more of a psychological thing.

Here, I just looked at the temperatures on each race day.

Looks complicated, but it’s just the range of temperatures each yearThe above chart is called a box-and-whisker plot.

It shoes the range of temperatures for the race day each year.

The box shows where the temperature was for 50% of the time.

The whiskers show where the temperature was the rest of the race.

It jumps right out at you — 2018 was not only hotter, but the temperature changed a huge amount during the race.

Much more than any other year!2015: finish times got longer as the temp went upHere’s a chart of different temperatures during the 2015 race vs finish times for each runner.

It’s pretty clear that the hotter it got, the slower the runners were.

The chart even gives the regression equation of the relationship.

More maths: every year seems to have a similar relationship.

The last column in the above table shows the correlation coefficient.

There is definitely a correlation.

Except in 2018.

A mere 600 metres to finish but I was in a dark dark placeHmmm that’s strange.

Didn’t we just show that 2018 was the hottest year?.And didn’t we show that this was also the year where runners slowed down the most?.A potential explanation is that 2018 was so hot from the start that it didn’t matter how the temperature changed during the day.

After regressions, I built a number of classifiers for the data.

If you’re curious about the results there then let’s chat, but I’ll keep it off this page to spare everyone else.

Always pre-prepare your excuse ????So it appears that my defence is reasonably well founded.

2018 was hotter than every other year.

It was also the year when runners slowed down the most.

And even in other years, the hotter the temperature the slower the runners were.

Case closed, right?Felt like that guy behind me, but there’s always energy for a photoWell, perhaps not.

I don’t doubt that 2018 was the hottest year (even the Daily Express agrees, and they are never wrong).

It’s also pretty clear from the data that runners slowed more in 2018 than in any other year before that.

But I’m skeptical about the evidence that in a given race, runners who finished in hotter temperatures were slower.

If they took 5 hours to complete the race then finished later in the day, and the temperature is always higher then — right?Anyway.

Let me know what you think.

Do I have a good excuse or should I just admit I wasn’t fit enough?.This April 2019 I get another chance to break the 3 hour barrier in Brighton Marathon.

Praying for cool air!.????????.. More details