Let's consider the following histogram:
The bell-shaped shape is the typical finish distribution you would expect for a marathon: a few finishers are very fast, a few one are among the slowest. Most runners are in the middle. One can also see extra runners around 3:30 and 4:00 ; human beings like round numbers, and pacers target for round times.
Now, let's compare this with the distribution of finish times at Boston marathon 2014:
Notice the difference ? It looks like the histogram has been pushed towards the left, ie towards the fastest times. Indeed, Boston is one of the few marathons in the world you have to qualify for.
If we look closer at the results for each age division, we can see that times are more or less distributed around the qualifying time standard:
- Statistics for Boston marathon 2014
- Statistics for Paris marathon 2014
- Boston qualifying times for 2015