As an example, for a long time Germany used a way to measure unemployment that yielded consistently higher numbers than most of the rest of the world. So any honest international comparison had to make adjustments.

See https://en.wikipedia.org/wiki/Literacy_in_the_United_States

> In many nations, the ability to read a simple sentence suffices as literacy, and was the previous standard for the U.S. The definition of literacy has changed greatly; the term is presently defined as the ability to use printed and written information to function in society, to achieve one's goals, and to develop one's knowledge and potential.[3]