I'm trying to understand the section of the research article and they refer to a quadratic effect, a cubic effect, and a quadric effect. If anyone can shed any light on this at all, I'd very much appreciate it.
Thank you everyone. Yeah, it was quadric, not quartic. I had forgotten that ^2 was quadratic and not just called squared, so I thought they both referred to ^4 in some way. Also, a clear typo in one of the tables where 'quadratic' was used twice instead of quadratic and quadric didn't help.