是的，to which…是定语从句，修饰前面的名词。the extend to which…意思是“在多大程度上”，这是一个常用表达。又如：
The extent to which your diet is successful depends on your willpower. 节食能有多大的成效取决于你的意志。
Languages vary in the extent to which they rely on word order. 语言对词序的依赖程度各不相同。
They experimented on the extent to which parents’ violence has an effect on their children. 他们研究了父母的暴力会对孩子产生多大的影响。
They examined the extent to which (=how much) age affected language-learning ability. 他们调查了年龄会在多大程度上影响语言学习能力。
the amount to which, the level to which 的用法也类似。如：
the amount to which something is filled with people or things 密集程度（侧重从数量上考虑程度）
the level to which something is limited 某事物被限制和程度或范围
