"To know the variables" means to understand and be aware of all the factors or things that can affect a situation, problem, or outcome. Full definition
The height of arrogance is in making big risky bets believing you can predict the future when most know variables are already public. (newtraderu.com)
I can't remember correct definition of efficient market but it's something like, price reflect value, based on a current known variable, s and possible future variables. (greaterfool.ca)
Alastair points out that the model they use doesn't deal with known variables, has initial presumptions that have been shown to be incorrect and that their sample is essentially too small. (realclimate.org)