It was done after the debate and supposedly damns the candidates. It actually shows otherwise.
The second link explains a lot and has some useful graphs to compare writers to various grade levels.
For one thing, it explains why Trump is attractive to more voters of differing levels and why Cruz come across as the smartest candidate there. It’s not true but it’s how it is perceived.
It’s all about reaching audiences. Numero uno of that is Rush no one does it better.