Accordion Icons: Which Work Best?

So what icon is the most reliable to show expansion and collapsing for accordions? Is there really any noticeable difference between carets, chevrons, arrows, and triangles?
Well, research shows that there is some difference indeed. But what’s more interesting is that split menus are harmful, why it's better to not have icons and text labels link to different actions, and why the caret is the safest icon choice. Let’s dive in!No Icon = Opening The Page
The findings aren’t very surprising: