What Is the Relationship between a coin’S Market Capitalization and Its’cost to Attack’?

There is a strong inverse relationship between a coin's market capitalization and the relative 'cost to attack' (as a percentage of market cap). Smaller market cap coins often have a low absolute cost to attack because their total hash rate is small and can be rented cheaply.

While a high market cap coin's absolute cost to attack is high, the relative cost can still be low if the coin's hash rate is shared with other, larger networks (e.g. merged mining).