communication

You automatically assume that fluent speech equals high intelligence.

A 2006 study found that writers who use complex, unnecessary words are perceived as less intelligent.

The study was conducted by Daniel M. Oppenheimer in 2006 and focused primarily on written materials, not spoken language.

Complexity is often a barrier to being taken seriously.

Where this comes from

Study: Oppenheimer (2006)
What the check found: The study exists and the core finding is accurate, but the year is incorrect (2006 instead of 2010). The study also focused on written text rather than spoken language.
Confidence: Solid, with limits

One of these every day, and every one names the study it came from. When a finding is contested, it says so.