Yes, statistical analysis of their victories and defeats. It's an excellent book. I'd recommend it.
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I've commonly heard that Spartans were good at fighting but bad at war. Turns out that a band of illiterate warriors is largely a bad idea for an army composition. If the war goes on too long, they simply run out of supplies and leave (Or, if they're forced to fight, they run out of supplies and lose)
But there is also the truth and history that we want to learn about sometimes. I think the Spartan mythos was useful to other Greeks, and the Spartan mythos remains useful today (in the form of US Marines).
But the myth is distinct from the real and actual history. It is beneficial to peel back the propaganda sometimes and analyze history for what it is.
Spartans did not win battles more often than others. Spartans couldn't field an army for extended periods of time. Etc. Etc. And yet we have these stories and written history of how great a warrior they were.
Thus: they probably were good at fighting (almost universally accepted). But war is more than just a fight. All the other bits of war were hampered by Spartan society, most noticably their illiteracy.
I don’t care about Sparta one way or another. But simply “looking at numbers” can be deceiving.