adverb
Used to indicate that something is more or less than expected when compared to a standard or other things. Often translates to 'for a ...' or 'considering ...'.
See also: 割合
この冬は割合に暖かい。
This winter is comparatively warm.
試験は割合に簡単だった。
The exam was relatively easy.
Adverbial form of the noun 割合 (わりあい, 'ratio, proportion'), with the particle に. The comparative sense developed from the idea of 'in proportion to'.