ogrisel/scikit-learn — comment on commit b866ef92e2d5c785e0fa65856d670d34d97f40fe
File: doc/faq.rst line 121
By satra:

this is a perfect place to point out that just like beauty, "accuracy is in the eyes of the application" - i.e. there is no absolute standard. we can define chance performance and perfect performance and everybody understands higher is better, but few people consider what the typical situation, i.e the scores in between chance and perfect, means. how much "better" than chance is good? and this is where the notion of what you are trying to get is important. if i am comparing algorithms, then higher is better as long as their confidence intervals do not overlap. if i'm doing a task such as diagnosing tumors, the usability of the number really lies more on the reducing false negatives.