Concerning decathlon, you can start all kinds of statistics.
Of course you can simply put up a list of all decathlon results ever reached and find out, who is among the most successful decathletes of all time.
You could also look at the single events to find out, who is best in pole vault, shot put and any other discipline you like.
Another possibility might be to look separately at throwing / running / jumping events to discover the best throwers / jumpers / runners among the athletes.
These are just some ways to analyse decathlon results.
You can find a lot of statistics already collected on the following pages:

Estonian Decathlon
Tilastopaja