"It is too unreliable when you're talking about messing with someone's career," said Gayle Fallon, president of the Houston Federation of Teachers.
She said many teachers don't understand the calculations. The general formula for the "linear mixed model" used in her district is a string of symbols and letters more than 80 characters long:
y = Xβ + Zv + ε where β is a p-by-1 vector of fixed effects; X is an n-by-p matrix; v is a q-by-1 vector of random effects; Z is an n-by-q matrix; E(v) = 0, Var(v) = G; E(ε) = 0, Var(ε) = R; Cov(v,ε) = 0. V = Var(y) = Var(y - Xβ) = Var(Zv + ε) = ZGZT + R.
"It's doctorate-level math," Fallon said.
Does Ms. Fallon have a doctorate in math? If not, how does she know the method is unreliable?
That isn't really the point. The point is that the teachers themselves can't really tell if the method is reliable or not, and hence cannot have any trust in the system. Trust is the real issue.