Florence, OneRepublic, lana all obviously write with few co-writers.
In fact, every single one of my favorites either write everything themselves or at least with just a little help (excluded pink and katy, but that makes sense, since they're pop, but STILL I'm convinced they write the majority of their music/songs).
What the hell, where are people getting these interesting percentages?

for example, I truly doubt Rihanna write 80% of unapologetic